Research Article Open Access
Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
R.Suresh R1, Balakumar R1, Krishnakumar N1, Saleem H2* and Subashchandrabose S1,3*
1Centre for Research and Development, PRIST University, Thanjavur, Tamilnadu, India-613403
2Department of Physics, Annamalai University, Annamalai nagar, Tamil Nadu, India-608 002.
3Centre for Functionalized Magnetic materials (FunMagMa), Immanuel Kant Baltic Federal University-236000, Kaliningrad, Russia.
*Corresponding author: S. Subashchandrabose, Centre for Research and Development, PRIST University, Thanjavur, Tamilnadu, India-613403. Tel: +91 9976853476; E-mail: @
Received: February 8, 2018; Accepted: February 24, 2018; Published: March 1, 2018
Citation: Subashchandrabose S, R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations. Int J Mol Theor Phy 2(1): 1-22.
Abstract Top
In the present investigation we investigate the structural, spectral and Molecular Orbitals (MO’s) properties of Naringin compound. It is a bioflavonoid, present in the fruits; it is responsible for bitter taste in fruits. The Naringin has a flavanone-7-O-glycoside between the flavanone naringenin and the disaccharide neohesperidose. It consists of naringenin (ring A-C), D-glucose (ring D) and L-rhamnose (ring E). Our aim is to predict the molecular structure and investigate the insights of the Naringin molecule. Besides that to study the vibrational behavior of Naringin, the FT-IR and FT-Raman spectra were recorded in the ranges of 4000-400cm-1 and 3500-50cm-1 respectively, and to study the frontier molecular orbitals, the UV-Visible spectrum was recorded in the range of 500-200nm. In addition to that the geometry of Naringin molecular structure was optimized by Density Functional Theory (DFT/B3LYP) calculation using 6-31g (d, p) level of basis set. For the optimized structure, vibrational spectral calculation was performed by the same level of theory calculation, furthermore, interpreted the calculated spectra of Naringin in terms of TED analysis. Moreover, to explain the inter and intra molecular charge transfer within the molecule the Natural Bond Orbital analysis (NBO) was performed, NBO analysis gave us a clear picture about hyperconjugative interaction energy between the donor (i) and acceptor(j) bond orbitals. In addition to that, the first order hyperpolarizability (β0), polarizability (α) and dipole moment (μ) of Naringin was computed. The frontier MO’s (HOMO-LUMO) of Naringin was analyzed by TD-B3LYP level of theory using 6-31g (d, p) level of basis set. Finally, the experimentally recorded results were compared with computed values, the agreement and discrepancies were studied carefully.

Keywords: FT-IR; FT-Raman; TED; NBO; Naringin;
Introduction
Flavonoids are naturally occurring phenolic compounds with a diverse range of bioactivities [1]. Among flavonoids, Naringin has great potential especially in the food and pharmaceutical industries due to their recognized antioxidant, anti-inflammatory, anti-ulcer, and hypocholesterolemic effects, whereas the Naringenin has also shown anti-mutagenic and neuroprotective activities [2]. Naringin is a ‘flavanone glycoside found in grape and citrus fruits. It has the distinct bitter taste of grapefruit juice. Its molecular formula is C27H32O14 and molecular weight is about 580.4g/mol, it consists of L-rhamnose and D-glucose with Naringenin at the 7-carbon portion [3]. It is moderately soluble in water [4]. It has been reported to protect against oxygen free radical-stimulated K_ permeability [5], metal chelating, antioxidant and free radical scavenging properties [6], Naringin, a major bioflavonoid in grapefruit, it has been shown to reduce radiation-induced damage to DNA [7]. It also acts as the inhibitor of VEGF (Vascular Endothelial Growth Factor) release, which causes angiogenesis and has been proven to be effective against ethanol injury in rats [8, 9].

Since the Naringin flavonoid having a wide application in above-mentioned fields, we investigate the structure geometry, vibrational spectra, Frontier Molecular Orbitals (FMOs), inter and intramolecular interactions by experimental and computation methods such as FT-IR, FT-Raman, UV-Visible spectra, DFT and Time dependent-DFT calculations. To the best of our knowledge, there is no such an article being published till now.
Experimental Details
FT-Raman and FT-IR Spectra
The solid form of Naringin compound was purchased from sigma Aldrich Company USA. The FT-Raman spectra was recorded in the region 3500-50cm-1 using the FT-Raman spectrometer with Nd:YAG laser source, and 1064nm as a excitation wavelength with spectral resolution of 4cm-1 on a Bruker model IFS66V spectrophotometer equipped with an FRA 106 FT-Raman module accessory. The spectral measurements were carried out at Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram, Kerala, India. The FT-IR spectrum of this compound was recorded in the region 400-4000 cm-1 on an IFS 66V spectrophotometer using the KBr pellet technique. The spectrum was recorded at room temperature, with a scanning speed of 10 cm-1 per minute and at the spectral resolution of 2.0 cm-1 in CSIL Laboratory, Annamalai University, and Tamilnadu, India. The ultraviolet absorption spectrum of Naringin was recorded in the range of 200-500 nm using a shimadzu UV-2401PC, UV-Visible recording spectrometer. The UV pattern is taken from a 10-5 molar solution of Naringin dissolved in methanol.
Computational Details
The entire calculations were performed at DFT level on a Pentium 1V/3.02 GHz personal computer using Gaussian 03W Program package [10], invoking gradient geometry optimization [11]. In this study, the DFT/B3LYP/6-31G (d, p) method has been utilized for the computation of molecular structure, vibrational frequencies and energies of optimized structures. By combining the results of the GAUSSVIEW program with symmetry considerations, vibrational frequency assignments were made with a high degree of accuracy and also the scaled quantum mechanics calculation was used to identify the vibrations [12, 13].

It should be noted that Gaussian 03W package able to calculate the Raman activity. The Raman activities were transformed into Raman intensities using Raint program by the expression [14]:
I i =10 -12 ×(ν 0 -ν i ) 4 × 1 ν i ×RA i      (1) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcaaMaaeysaO WaaSbaaKqaGfaacaqGPbaabeaajaaycaqG9aGaaeymaiaabcdakmaa Caaajeaybeqaaiaab2cacaqGXaGaaeOmaaaajaaycaqGxdGaaeikai aab27akmaaBaaajeaybaGaaeimaaqabaqcaaMaaeylaiaab27akmaa BaaajeaybaGaaeyAaaqabaqcaaMaaeykaOWaaWbaaKqaGfqabaGaae inaaaajaaycaqGxdGcdaWcaaqcaawaaiaabgdaaeaacaqG9oGcdaWg aaqcbawaaiaabMgaaeqaaaaajaaycaqGxdqcaaKaaeOuaiaabgeakm aaBaaajeaybaGaaeyAaaqabaGccaqGGaGaaeiiaiaabccacaqGGaGa aeiiaiaabIcacaqGXaGaaeykaaaa@594A@
Where Ii is the Raman intensity, RAi is the Raman scattering activities, νi is the wavenumber of the normal modes and ν0 denotes the wavenumber of the excitation laser [15].
Results and Discussion
Molecular Geometry
Molecular structure of the Naringin was optimized by using DFT/B3LYP level of theory calculation using 6-31G (d, p) basis set. The optimized molecular structure along with numbering scheme is given in Figure 1. It is belongs to C1 point group symmetry. To the best of our literature survey, the crystal data of this molecule is not available till date [16]. So that, the optimized geometric parameters of Naringin is compared with Naringenin, quercetin and some flavones. It consists of L-rhamnose and D-glucose with naringenin at the 7-carbon, Naringin structure has 8 hydroxyl groups; it leads the molecule more inter-molecular hydrogen bonding interactions. The carbonyl present in naringenin forms intra-molecular hydrogen bonding interaction between carbonyl and hydroxyl groups. Due to this, the bond lengths of C3-C8 (1.424), C8-C10 (1.398) in ring A and C4-C5 (1.516 Å) in ring B are positively elongated with C-C bond lengths (~1.4 Å) in ring C as well as with literature values [16].

Zhang et al. observed the C=O and C-O bond lengths are about 1.235 and 1.427 Å, respectively for 5, 6, 7, 4’-tetramethoxy isoflavone [17]. These observed values are in line with the calculated values (C4=O14: 1.243 and C8-O15: 1.337Å) of Naringin molecule. Moreover, there is a shrink in bond length of C8-O15 due to delocalization of π-electron from C4=O14. On comparing the C-C bond length in ring D, E with ring A, B and C are higher (~1.5 Å) due to the boat form of ring D and ring E. In ring A, the angle of C8- O15-H16 and C3-C8-C10 are about 106.52º and 120.74º respectively. These angles are negatively deviated from the angles of C24- O27-H28 (109.21º) and C22-C24-C20 (119.78º) is due to the electron localized in ring E. The calculated bond lengths, bond angles and dihedral angles are listed in Table S1 (Supporting information).
Figure 1: Optimized Molecular structure of Naringin.
Table S1: The optimized bond lengths, bond angles and dihedral angles of Naringin using B3LYP/6-31G(d,p) basis set.

Parameters

B3LYP/
6-31G(d,p)

Exp.

Parameters

B3LYP/
6-31G(d,p)

Exp.

Bond lengths (Å)

 

 

Bond length Contd…

 

 

C1-C5

1.533

 

C30-O40

1.427

 

C1-O13

1.447

1.376

C30-H59

1.094

 

C1-C17

1.509

1.467

C31-C33

1.555

 

C1-H73

1.100

 

C31-O38

1.424

 

C2-C3

1.420

1.386

C31-H64

1.095

 

C2-C7

1.385

1.388

C32-C33

1.544

 

C2-O13

1.361

1.365

C32-O34

1.442

 

C3-C4

1.447

1.449

C32-C54

1.521

 

C3-C8

1.424

1.406

C32-H66

1.097

 

C4-C5

1.516

1.455

C33-O36

1.428

 

C4-O14

1.243

1.238

C33-H65

1.095

 

C5-H9

1.098

 

O36-H37

0.974

 

C5-H68

1.093

 

O38-H39

0.977

 

H6-C7

1.083

0.930

O40-C41

1.443

 

C7-C11

1.404

1.378

C41-C42

1.536

 

C8-C10

1.398

1.364

C41-O46

1.394

 

C8-O15

1.337

1.355

C41-H47

1.095

 

C10-C11

1.398

1.399

C42-C43

1.529

 

C10-H12

1.081

0.930

C42-O48

1.418

 

C11-O35

1.368

 

C42-H63

1.100

 

O14-H16

1.685

 

C43-C45

1.550

 

O15-H16

0.995

0.910

C43-O50

1.422

 

C17-C18

1.399

1.389

C43-H62

1.101

 

C17-C19

1.400

1.392

C44-C45

1.539

 

C18-C20

1.393

1.383

C44-O46

1.437

 

C18-H21

1.085

0.930

C44-H60

1.100

 

C19-C22

1.391

1.377

C44-C69

1.519

 

C19-H23

1.087

0.930

C45-O52

1.424

 

C20-C24

1.400

1.385

C45-H61

1.099

 

C20-H25

1.088

0.930

O48-H49

0.978

 

C22-C24

1.399

1.376

O50-H51

0.970

 

C22-H26

1.085

0.930

O52-H53

0.966

 

C24-O27

1.365

 

C54-O55

1.412

 

O27-H28

0.966

 

C54-H57

1.103

 

C29-C30

1.549

 

C54-H58

1.095

 

C29-O34

1.410

 

O55-H56

0.968

 

C29-O35

1.412

 

C69-H70

1.095

 

Bond lengths (Å)

 

 

Bond lengths (Å)

 

 

C29-H67

1.096

 

C69-H71

1.092

 

C30-C31

1.534

 

C69-H72

1.093

 

Bond Angles (˚)

 

 

Bond Angles (˚)

 

 

C5-C1-O13

109.96

120.85

C17-C19-C22

121.24

 

C5-C1-C17

113.40

128.80

C17-C19-H23

119.67

 

C5-C1-H73

108.54

 

C22-C19-H23

119.09

 

O13-C1-C17

108.05

111.15

C18-C20-C24

120.00

 

O13-C1-H73

107.39

 

C18-C20-H25

120.02

 

C17-C1-H73

109.33

 

C24-C20-H25

119.98

 

C3-C2-C7

121.19

121.70

C19-C22-C24

119.62

 

C3-C2-O13

121.41

122.03

C19-C22-H26

121.37

 

C7-C2-O13

117.40

116.03

C24-C22-H26

119.01

 

C2-C3-C4

120.71

119.12

C20-C24-C22

119.78

 

C2-C3-C8

118.46

118.52

C20-C24-O27

122.78

 

C4-C3-C8

120.66

122.33

C22-C24-O27

117.44

 

C3-C4-C5

115.78

115.93

C24-O27-H28

109.21

 

C3-C4-O14

123.06

 

C30-C29-O34

112.11

 

C5-C4-O14

121.13

 

C30-C29-O35

107.21

 

C1-C5-C4

111.08

122.03

C30-C29-H67

109.79

 

C1-C5-H9

109.46

 

O34-C29-O35

112.95

 

C1-C5-H68

110.97

 

O34-C29-H67

104.98

 

C4-C5-H9

108.41

 

O35-C29-H67

109.80

 

C4-C5-H68

109.43

 

C29-C30-C31

108.12

 

H9-C5-H68

107.38

 

C29-C30-O40

112.41

 

C2-C7-C6

121.16

 

C29-C30-H59

108.86

 

C2-C7-C11

118.76

118.72

C31-C30-O40

107.36

 

C6-C7-C11

120.06

 

C31-C30-H59

110.16

 

C3-C8-C10

120.74

120.20

O40-C30-H59

109.91

 

C3-C8-O15

120.54

121.20

C30-C31-C33

108.94

 

C10-C8-O15

118.71

116.80

C30-C31-O38

111.22

 

C8-C10-C11

118.63

120.35

C30-C31-H64

109.10

 

C8-C10-H12

118.62

 

C33-C31-O38

109.57

 

C11-C10-H12

122.70

 

C33-C31-H64

109.72

 

C7-C11-C10

122.22

120.48

O38-C31-H64

108.27

 

C7-C11-O35

114.01

 

C33-C32-O34

109.67

 

C10-C11-O35

123.77

 

C33-C32-C54

113.78

 

C1-O13-C2

116.59

120.85

C33-C32-H66

109.20

 

C8-O15-H16

106.52

 

O34-C32-C54

105.99

 

Bond Angles (˚)

 

 

Bond Angles (˚)

 

 

C1-C17-C18

121.16

 

O34-C32-H66

109.00

 

C1-C17-C19

120.24

122.71

C54-C32-H66

109.07

 

C18-C17-C19

118.55

117.19

C31-C33-C32

110.36

 

C17-C18-C20

120.80

119.30

C31-C33-O36

109.48

 

C17-C18-H21

119.55

 

C31-C33-H65

109.20

 

C20-C18-H21

119.64

 

C32-C33-O36

111.44

 

C32-C33-H65

110.90

 

C32-C54-O55

112.01

 

O36-C33-H65

105.31

 

C32-C54-H57

108.61

 

C29-O34-C32

114.52

 

C32-C54-H58

108.86

 

C11-O35-C29

119.78

 

O55-C54-H57

111.97

 

C33-O36-H37

105.12

 

O55-C54-H58

107.36

 

C31-O38-H39

104.36

 

H57-C54-H58

107.91

 

C30-O40-C41

116.34

 

C54-O55-H56

106.57

 

O40-C41-C42

108.94

 

C44-C69-H70

110.15

 

O40-C41-O46

108.38

 

C44-C69-H71

109.57

 

O40-C41-H47

107.95

 

C44-C69-H72

110.51

 

C42-C41-O46

113.73

 

H70-C69-H71

109.00

 

C42-C41-H47

109.52

 

H70-C69-H72

108.38

 

O46-C41-H47

108.15

 

H71-C69-H72

109.20

 

C41-C42-C43

110.15

 

C32-C54-O55

112.01

 

C41-C42-O48

110.63

 

C32-C54-H57

108.61

 

C41-C42-H63

108.33

 

C32-C54-H58

108.86

 

C43-C42-O48

107.85

 

O55-C54-H57

111.97

 

C43-C42-H63

108.91

 

O55-C54-H58

107.36

 

O48-C42-H63

110.96

 

H57-C54-H58

107.91

 

C42-C43-C45

111.34

 

C54-O55-H56

106.57

 

C42-C43-50

109.69

 

C44-C69-H70

110.15

 

C42-C43-H62

108.26

 

C44-C69-H71

109.57

 

C45-C43-50

108.45

 

C44-C69-H72

110.51

 

C45-C43-H62

108.29

 

H70-C69-H71

109.00

 

50-C43-H62

110.82

 

H70-C69-H72

108.38

 

C45-C44-O46

109.80

 

H71-C69-H72

109.20

 

C45-C44-H60

107.84

 

Dihedral angles (º)

 

 

C45-C44-C69

112.91

 

O13-C1-C5-C4

-54.56

 

O46-C44-H60

110.48

 

O13-C1-C5-H9

65.13

 

O46-C44-C69

106.72

 

O13-C1-C5-H68

-176.53

 

H61-C44-C69

109.10

 

C17-C1-C5-C4

-175.65

 

C43-C45-C44

111.98

 

C17-C1-C5-H9

-55.96

 

Bond angles (Å)

 

 

Dihedral angles (º)

 

 

C43-C45-O52

112.34

 

C17-C1-C5-H68

62.38

 

C43-C45-H61

106.70

 

H73-C1-C5-C4

62.65

 

C44-C45-O52

105.67

 

H73-C1-C5-H9

-177.67

 

C44-C45-H61

108.62

 

H73-C1-C5-H68

-59.33

 

O52-C45-H61

111.54

 

C5-C1-O13-C2

51.63

 

C41-O46-C44

117.45

 

C17-C1-O13-C2

175.88

 

C42-O48-H49

108.56

 

H73-C1-O13-C2

-66.28

 

C43-50-H51

105.73

 

C5-C1-C17-C18

80.31

 

C45-O52-H53

107.93

 

C5-C1-C17-C19

-97.28

 
Exp. – Experimental
Vibrational Assignments
The Naringin molecule contains 73 atoms (including 8 –OH group, one methylene and methyl groups); hence it can have 213 normal modes of vibrations. To the best of our knowledge, there is no complete vibrational spectroscopic study carried out on Naringin. In the present investigation the FT-IR and FTRaman spectra were recorded in the region of 4000-400cm-1 and 3500-50cm-1, respectively. Stimulated IR and Raman spectra were constructed and compared with experimental spectra. The combined spectrum of FT-IR showed in Figure 2 and the FT-Raman spectrum showed in Figure 3. Similarly, Observed frequencies and calculated wave numbers are compared and listed in Table 1, also provided a detail results in Table S2 (Supporting information). The frequency calculation was performed by using B3LYP level of theory using 6-31G (d, p) basis set. The TED for all fundamental vibrations is calculated using SQM method.
C-H Vibrations
The heteroaromatic structure shows the presence of C-H vibration in the region 3100-3000 cm-1, which is the characteristic region for the ready identification of C-H stretching vibration [18]. In this region, the bands are not affected appreciably by nature of the substituent. In the present work, the C-H aromatic stretching frequency observed at 3071 cm-1 as a weak band in FT-Raman and its corresponding calculated wavenumber is 3083 cm-1 (mode numbers: 202). For the same mode five more harmonic vibrations are also appeared (mode numbers: 200, 201, 203-205). As expected these modes are pure stretching modes as it evident from the TED column (their contribution ~95%). The FT-IR bands 2890-2970 cm-1 (weak) and FT-Raman bands 2939, 2958, 2976 cm-1 (weak) are assigned to C-H stretching in ring B and ring D respectively. These assignments are comparable with harmonic frequencies 2888, 2939, 2943, 2952, 2965 and 2985 cm-1 (mode numbers: 185, 191, 193-196) and also find support from TED. The mode numbers: 183, 184, 186, 188 and 192 are
Figure 2: The combined experimental and theoretical FT-IR spectra of Naringin.
Figure 3: The combined experimental and theoretical FT-Raman spectra of Naringin.
assigned to νC-H in ring E. The in-plane bending of C-H is observed at 1089, 1178 and 1296 (strong) in FT-IR and 1002 cm-1 in FTRaman spectra. The calculated wavenumbers in the range 990- 1312 cm-1 (mode numbers: 101, 117, 125-128, 140, 143, 145- 147) are assigned to δC-H with considerable TED value. The Outof- plane bending of τC-H mode is observed at 896, 812, 607 cm-1 in FT-Raman and 919 and 608 cm-1 in FT-IR spectra, whereas the harmonic values are in the range of 605-922 cm-1 (mode nos: 67, 68, 80-82, 86, 94, 95). These assignments are in agreement with literature values [18-19].
Methyl Group (CH3) Vibrations
The C-H stretching mode in CH3 occurs at lower wavenumber than those of the aromatic ring (3000-3100 cm-1). The asymmetric stretching mode of the CH3 group is expected to occur in the region of 2980 cm-1 and the symmetric one is at 2870 cm-1 [20- 21]. The methyl group (CH3) has three stretching vibrations, namely one symmetric and two asymmetric modes [22]. In this study, the computed wavenumbers for the CH3 (asy) stretching and CH3 (sym) stretching are 3021, 3008 cm-1 (mode numbers: 199, 198) and 2938 cm-1 /mode no: 190, respectively. These modes are supported by TED and above literature. These modes are 100% (TED) pure for CH3 stretching vibration.

Two asymmetric CH3 bending, one symmetric CH3 bending, two CH3 rocking and one CH3 torsional vibrations are possible [22]. The methyl group symmetric deformation absorbs moderately to strong in the range 1365±25 cm-1 and asymmetric methyl deformations in the region 1390-1480 cm-1 [23]. Based on the above conclusion the observed bands 1453/1456 (FT-IR/ Raman) and 1363 cm-1/FT-IR are attributed to δCH3 (asym) and δCH3 (sym), respectively. The methyl rocking generally appears in the region 1050±30 and 975+45 cm-1 [24], as a weak moderate or sometimes strong band, the wavenumber of which is coupled to the C-C stretching vibrations, which occur in the neighborhood of 900 cm-1. The FT-Raman band 1122 cm-1 (medium strong) and
Table S2: The vibrational assignments of Naringin using Scaled Quantum Mechanics method (B3LYP/6-31G(d,p)).

Mode
No.

Scaled
B3LYPa

FT-IR

FT-Raman

IbIR

IcRaman

Vibrational assignments
TEDd  (≥ 10)>

1

3

 

 

0.05

79.30

τC29-O35-C11-C7(46)+ τC29-O35-C11-C10(45)

2

14

 

 

0.00

13.63

τC32-O34-C29-O35(11)+ τC41-O40-C30-C29(14)

3

18

 

 

0.02

28.67

τC11-O35-C29-C30(21)+ τC11-O35-C29-O34(18)

4

23

 

 

0.13

100

τC18-C17-C1-O13(15)+ τC19-C17-C1-C5(23)+ ΓC19-C17-C1-O13(16)

5

33

 

 

0.01

6.17

τC42-C41-O40-C30(10)

6

34

 

 

0.13

17.21

τCCCC(3)

7

38

 

 

0.10

22.75

τCOCC(30)

8

39

 

 

0.16

20.95

τC2-O13-C1-C17(22)

9

50

 

 

0.04

3.72

τC44-O46-C41-O40(16)

10

60

 

 

0.25

4.79

τCCCC(10)+ τOCCC(13)

11

76

 

 

0.02

2.30

τOCOC(10)

12

82

 

86s

0.37

1.09

τcccc(16)+ Γoccc(13)

13

95

 

 

0.09

1.15

δC11-O35-C29(10)+ τC41-O40-C30-C31(10) 

14

103

 

 

0.29

1.01

τOCCO(10)

15

111

 

 

0.62

0.54

 τOCCC(13)

16

114

 

 

0.46

0.70

τO55C54C32C33(10)

17

126

 

 

1.04

1.01

δC41-O40-C30(12)+ τC44-O46-C41-O40(11)

18

132

 

140w

0.14

2.02

τccco(10)

19

143

 

 

0.34

2.22

τOCCC(10)

20

169

 

168w

0.50

1.30

δccc(15)

21

182

 

 

0.21

1.36

νCC(10)+δCCC(13)+ τOCCC(10)

22

186

 

 

2.01

2.70

δOCC(10)

23

206

 

 

3.04

2.61

δOCC(10)

24

209

 

 

0.08

0.99

τHCCC(37)+ τHCCO(18)+ τHCCH (24)

25

215

 

 

0.36

0.57

τC11-C10-C8-O15(20)

26

220

 

220w

1.31

0.59

δC45-C44-C69(14) +τHCCC (10)

27

228

 

 

1.85

2.90

τH56O55C54C32(10)

28

229

 

 

0.72

0.55

τO52C45C44(10)

29

240

 

247w

8.53

3.46

τH56-O55-C54-C32(32)+ τH56-O55-C54-H57(22)+ τH56-O55-C54-H58(11)

30

256

 

 

0.40

1.88

δCCC(10)

31

267

 

 

0.80

0.96

τHOCC(10)

32

283

 

 

0.36

0.91

δCCC(10)+δOCC(10)

33

284

 

 

0.78

1.82

τC41O40C30(10)

34

293

 

 

0.48

0.62

τO38C31C30O40(10)

35

300

 

 

0.94

0.77

τOCCC(10)+ ΓOCCO(10)

36

309

 

 

0.43

0.82

δO55C54C32(16)

37

315

 

 

0.10

1.29

δOCC(10)

38

321

 

 

2.60

0.71

δOCC(15)+δCCO(10)

39

340

 

 

15.04

2.29

τH28-O27-C24-C20(47)+ τH28-O27-C24-C22(52)

40

345

 

 

0.70

0.27

δOCC(14)+δCCO(10)+τHOCC(11)

41

363

 

 

2.62

1.00

δOCC(11)+ τOCCC(13)

42

365

 

 

12.40

1.06

τH53-O52-C45-C43(29)+ τH53-O52-C45-C44(17)+ τH53-O52-C45-H61(22)

43

366

 

 

0.69

2.83

δOCC(10)

44

376

 

385w

0.98

0.86

δOCC (10)

45

395

 

 

6.04

1.46

τH51-O50-C43-C45(14)

46

399

 

 

4.05

0.83

δO27-C24-C20(20)+δO27-C24-C22(23)

47

402

 

 

2.25

0.27

δO27-C24-C20(11)

48

406

 

 

0.19

0.29

τC24-C20-C18-C17(18)+ τC24-C22-C19-C17(18)

49

409

 

 

3.30

1.23

τH51-O50-C43-C42(11)+ τΓH51-O50-C43-H62(12)

50

417

 

 

4.16

1.81

τH51-O50-C43-C42(15)

51

419

 

 

11.62

1.14

τH16-O15-C8-C3(31)+ τH16-O15-C8-C10(32)

52

432

 

 

0.49

1.84

τHOCC(13)

53

435

434w

 

5.92

0.45

τHCCC(10)

54

446

 

448w

4.02

0.95

δCCO(10)

55

476

 

469w

0.41

0.41

δCCO(10)

56

481

481w

 

1.63

1.09

τCCOC(11)+ τHOCC(12)  

57

497

 

 

2.25

0.71

δCCC(11)

58

503

 

 

3.69

1.57

τHOCC(13)

59

514

511w

 

0.30

0.99

δCOC(14)

60

517

 

 

3.71

0.52

δC10C8C3(10)

61

523

522w

520w

3.30

3.07

νCC(10)+νOC(10)+ τHOCC(22)+ τHOCH(10)

62

541

 

 

1.15

1.65

δCCC(10)

63

546

 

 

2.37

1.18

δCCC(10)

64

548

 

563w

1.26

1.93

νCC(10)

65

576

561w

 

0.31

0.67

δOCC(13)

66

597

 

 

2.97

1.77

δOCC(11)

67

605

608w

607w

2.01

0.48

τHCCC(10)

68

616

 

 

1.10

4.59

τCCCC(10)+ τCCCH(10)

69

621

626w

 

0.97

0.15

τCCCC(12)+ τOCCC(10)

70

630

637w

 

1.21

2.15

δCCC(35)

71

642

 

643w

0.81

3.90

νCC(16)

72

661

 

663ms

0.30

0.67

δCOC(12)

73

666

668w

 

4.51

0.24

τCCOC(14)

74

682

 

 

0.94

2.08

νCC(21)

75

700

702w

704w

7.31

0.71

τH37-O36-C33-C31(10)

76

706

 

 

2.47

0.58

τCCCC(26)

77

713

 

 

8.57

0.83

τHOCC(20)

78

718

730w

 

0.23

0.55

τCCCC(31)+ τOCCC(21)

79

752

743w

748w

14.50

0.21

τH49-O48-C42-C41(30)+ τH49-O48-C42-C43(27)+ τH49-O48-C42-H63(14)

80

774

 

 

5.37

0.49

τHOCC(22)+ τHOCH(10)

81

784

 

 

2.59

1.96

τH12-C10-C8-O15(20)+ τO35-C11-C10-H12(20)

82

788

 

 

2.02

1.41

τH25-C20-C18-C17(20)+ τC22-C24-C20-H25(14)+ τO27-C24-C20-H25(23)

83

794

 

 

4.26

2.11

νC69-C44(15)

84

796

 

 

2.84

2.84

νO27-C24(14)

85

805

 

 

1.86

1.69

νCC(18)+νOC(11)

86

812

 

812w

6.63

0.48

τC24-C22-C19-H23(13)+ τH26-C22-C19-C17(17)+ τO27-C24-C22-H26(21)

87

814

 

 

1.23

4.67

νO34-C32(18)

88

823

821ms

 

5.97

0.24

νCC(17)+ νOC(11)

89

848

835w

837w

1.61

2.71

νC18-C17(11)

90

856

 

 

0.95

0.28

νC33-C31(14)

91

871

864vw

864w

0.45

1.47

νC43-C42(15)

92

876

888w

 

2.61

0.89

νO13-C1(16)

93

877

 

 

6.17

0.34

νCC(22)+νOC(23)

94

910

 

896ms

0.22

0.34

τH21-C18-C17-C1(15)+ τC24-C20-C18-H21(11)+ τH25-C20-C18-H21(35)

95

922

919w

 

0.01

0.12

τH23-C19-C17-C1(12)+ τH23-C19-C17-C18(11)+ τH26-C22-C19-H23(36)

96

923

 

 

1.76

2.11

νO46-C44(17)+δH-C-C(13)

97

953

 

 

0.54

0.74

νO13-C1(11) +τHCCC (10)

98

961

 

 

1.34

1.10

νC45-C43(24)+δH72-C69-C44(11)+ τH70-C69-C44 (10)

99

963

 

 

2.63

0.87

νC31-C30(13)+νO36-C33(12)

100

987

986ms

982w

28.45

4.40

νO35-C29(20)

101

990

 

1002w

3.25

0.12

νCC(31)+δCCC(32)+δCCH(18)+δHCC(14)

102

1004

 

 

10.29

1.40

νO38-C31(11)

103

1011

 

 

38.88

0.64

νOC(16)+νCC(12)

104

1021

 

 

8.50

1.82

νOC(16)+ νCC(10)

105

1025

 

 

8.95

0.44

νCC(11)+ νCO(32)+νC69-C44(10)

106

1032

 

 

13.48

0.82

νC33-C32(14)

107

1038

 

 

15.47

0.66

νO40-C30(11)+νO55-C54(24)

108

1039

 

1039w

15.09

0.88

νC5-C1(14)+νC33-C32(14)

109

1040

1040s

 

3.50

3.12

νC5-C1(19)+νO13-C1(11)

110

1053

 

 

57.67

0.97

νC41-O40(20)+νO46-C41(18)+νO52-C45(18)

111

1063

1060s

 

33.94

1.22

νO13-C2(12)+νO15-C8(11)+νO55-C54(19)

112

1066

 

 

2.32

1.28

νO55-C54(16) +νCO(35)

113

1070

 

 

6.68

0.27

νCO(42)

114

1073

 

 

7.73

0.99

νCO(26)

115

1076

1071s

 

7.75

0.30

νO36-C33(19)

116

1082

 

1081ms

25.65

1.70

νO38-C31(15)+νC41-O40(11)+νO48-C42(11)

117

1087

1089s

 

1.36

0.95

νC22-C19(15)+δH26-C22-C19(14)

118

1095

 

 

15.05

0.57

νCO(18)

119

1100

 

 

12.86

1.28

νO48-C42(29)+νO52-C45(24)

120

1104

 

 

15.31

1.13

νC54-C32(11)

121

1107

 

 

12.96

0.88

νO50-C43(12)+νO52-C45(13)

122

1116

 

1122ms

8.29

0.35

δH53-O52-C45(11) +ΓHCCH(10)

123

1134

1136s

 

17.14

0.89

νO46-C41(15) +δCCH(10)

124

1142

 

 

3.17

2.44

νCO(19)+δCCH(14)

125

1152

 

 

14.20

1.00

δH21-C18-C17(10)+δH26-C22-C19(11)+δC24-C22-H26(12)

126

1153

 

 

2.97

0.92

δC24-C20-H25(10)+δH28-O27-C24(35)

127

1159

 

 

41.82

1.39

δHCC(14)+νC-O(23)

128

1175

1178s

 

2.39

0.59

νC10-C8(11)+δH12-C10-C8(13)+δH16-O15-C8(36)

129

1180

 

1185w

3.80

1.01

δH56-O55-C54 (24)+δCCH(10)+δH37-O36-C33(10)

130

1189

 

 

16.87

1.40

νC17C1(11)

131

1191

 

 

1.29

4.38

νC17-C1(18)

132

1201

 

 

5.32

0.05

δH51-O50-C43(17)

133

1203

1205s

1210s

12.61

4.78

νC4-C3(10)

134

1217

 

1215w

3.99

0.92

δH56-O55-C54(23)+δH58-C54-C32(12)+δO55-C54-H58(10)

135

1224

 

 

2.95

1.24

δH53-O52-C45(31)

136

1227

 

 

1.00

0.77

δH68-C5-C1(16)+δH68-C5-C4(15)

137

1245

 

 

0.96

0.93

δH57-C54-C32(13)

138

1248

 

 

7.72

0.73

δH49-O48-C42(14)

139

1254

 

1254w

41.32

6.38

νC4-C3(18)+δH16-O15-C8(19)

140

1256

 

 

1.73

0.24

δC43-C42-H63(11)

141

1259

 

 

8.28

2.64

νO27-C24(48)

142

1260

1263w

 

0.21

0.44

δHOC(14)

143

1279

 

 

0.17

1.21

δCCH(22)

144

1284

1282w

 

5.76

0.62

νC18-C17(12)

145

1297

1296s

 

1.93

1.15

νC45-C44(11)+ δO46-C44-H60(11)     

146

1310

 

 

6.20

1.91

δCCH(14)+δOCH(10)

147

1312

 

 

6.75

1.57

δCCH(13)+δOCH(10)+νCOCH(12)

148

1315

 

 

5.24

0.39

δH51-O50-C43(23)

149

1322

 

 

11.27

0.37

νCC(15)

150

1324

 

 

0.67

1.01

δH28-O27-C24(10)

151

1328

 

 

5.73

0.68

νCC(31)

152

1331

 

 

2.80

0.65

δCCH(10)

153

1334

 

 

4.28

0.43

δHOC(10)+ ΓHCCH(11)

154

1338

 

 

0.28

0.41

δO34-C32-H66(12)

155

1344

1341ms

 

7.17

1.37

δOCC(10)

156

1345

 

 

1.95

0.85

δHCC(25)

157

1349

 

1348ms

1.73

0.32

δHCC(13)+ΓHCCH (11)

158

1354

 

 

11.74

1.66

νO15-C8(12)

159

1357

 

 

3.85

0.21

δHOC(11)

160

1363

1363ms

 

1.88

0.30

δH71-C69-H72(20)+δHCC(18)

161

1370

 

1373w

0.57

0.51

δO34-C29-H67(12)+ ΓH59-C30-C29-H67(11)

162

1378

 

 

1.81

0.62

δHOC(12)+δHCO(10)

163

1383

 

 

2.41

0.34

δCOH(11)

164

1390

1393ms

 

12.51

0.24

δH39-O38-C31(33)

165

1399

 

 

2.48

0.80

δH37-O36-C33(26)+δH49-O48-C42(14)

166

1407

 

 

1.85

0.15

δH51-O50-C43(13) +δHOC(18)

167

1408

 

 

1.25

1.84

δH9-C5-H68(31) +ΓHCCC(25)+ΓHCCO(25)+ΓHCCH(10)

168

1411

 

 

10.03

1.15

δH37-O36-C33(15)+δH39-O38-C31(14)+δH49-O48-C42(17)

169

1420

 

 

13.63

0.06

νCC(29)+δCCH(11)

170

1423

 

 

1.69

0.28

δH56-O55-C54(13)+δH57-C54-C32(25)+ΓHOCC(19)

171

1429

 

 

16.16

0.06

δCCC(25)+δCCH(11)

172

1447

 

 

0.60

1.85

δH70-C69-C44(11)+δH70-C69-H71(24)+δH71-C69-H72(23)

173

1450

1453ms

1456ms

0.08

1.04

δH70-C69-H72(39) +ΓHCCH (10)

174

1466

 

 

0.99

1.30

δH57-C54-H58(30) +ΓHCCC(16)+ΓHCCO(16)+ΓHCCH(17)

175

1473

 

 

4.50

0.18

νC11-C7(17)

176

1502

1502ms

1502vw

12.45

0.71

νC18-C17(10)

177

1561

 

1574ms

20.70

0.96

νC3-C2(12)+νC8-C3(13)+νC11-C7(12)+νC11-C10(28)

178

1584

1582ms

 

3.29

0.61

νC18-C17(11)+νC19-C17(20)+νC24-C20(20)+νC24-C22(17)

179

1598

 

 

105.6

14.03

νC7-C2(22)+νC10-C8(20)+νC11-C7(12)

180

1610

 

 

7.51

8.61

νC20-C18(20)+νC22-C19(20)+νC24-C22(10)

181

1710

1646s

1643vs

36.22

7.18

νO14-C4(87)

182

2865

 

 

6.63

2.26

νC54-H57(70)+νC54-H58(30)

183

2873

 

 

0.65

0.73

νC41-H47(20)+νC45-H61(33)+νC43-H62(39)

184

2883

 

 

2.33

1.37

νC41-H47(39)+νC45-H61(11)+νC43-H62(49)

185

2888

2890w

 

3.24

1.62

νC1-H73(97)

186

2890

 

 

4.81

2.82

νC41-H47(29)+νC45-H61(51)+νC42-H63(19)

187

2904

 

2899ms

4.31

1.64

νC54-H57(28)+νC54-H58(69)

188

2907

 

 

13.46

0.29

νC41-H47(12)+νC43-H62(12)+νC42-H63(70)

189

2927

2929w

 

1.27

1.28

νC5-H9(87)+νC5-H68(11)

190

2938

 

 

1.52

3.52

νC44-H60(13)+νC69-H70(41)+νC69-H71(20)+νC69-H72(25)

191

2939

 

2939w

2.77

0.78

νC29-H67(97)

192

2941

 

 

4.72

1.18

νC44-H60(83)

193

2943

 

 

1.93

1.77

νC33-H65(23)+νC32-H66(73)

194

2952

 

2958w

1.95

0.98

νC31-H64(23)+νC33-H65(55)+νC32-H66(21)

195

2965

 

 

6.01

2.23

νC31-H64(73)+νC33-H65(22)

196

2985

2970w

2976w

2.17

1.36

νC30-H59(95)

197

3005

 

 

1.16

2.05

νC5-H9(10)+νC5-H68(89)

198

3008

 

 

4.42

0.75

νC69 H70(52)+νC69-H72(42)

199

3021

 

 

1.75

1.53

νC69-H71(71)+νC69-H72(25)

200

3042

 

 

3.33

1.72

νC20-H25(96)

201

3053

 

 

1.14

1.28

νC19-H23(95)

202

3083

 

3071w

0.88

0.96

νC18-H21(95)

203

3089

 

 

0.86

3.57

νC22-H26(94)

204

3096

 

 

0.89

1.70

νC10-H12(100)

205

3114

 

 

0.01

1.24

νC7-H6(100)

206

3425

3427s

 

69.82

1.75

νO48-H49(95)

207

3497

 

 

12.72

0.40

νO38-H39(92)

208

3555

 

 

17.68

0.40

νO36-H37(97)

209

3603

 

 

8.26

0.53

νO50-H51(100)

210

3653

 

 

5.73

1.47

νO15-H16(100)

211

3658

 

 

4.70

1.07

νO52-H53(100)

212

3672

 

 

7.22

1.56

νO27-H28(100)

213

3680

 

 

3.36

1.75

νO55-H56(100)

v: Stretching, δ: In-plane-bending, γ: Out-of-plane bending, vw: Very week, w: Week, m: Medium, s: Strong, vs: Very strong, Scaling factor: 0.9608(palafox, 2000),
b Relative IR Absorption intensities normalized with highest peak absorption equal to 100,
c Relative raman intensities calculated by equation (2.1) and normalized to 100.
d Total energy distribution calculated at B3LYP/6-31G(d,p) level.
harmonic bands 961, 1116 cm-1 (mode numbers: 98, 122) are assigned as rocking modes of CH3. The torsion vibrations are not observed in the FT-IR spectrum because this appears at very low frequency. The FT-Raman experimental band observed at 220 cm-1 shows an excellent agreement with theoretical results. These assignments support from the work of Sundaraganesan et al. and are within the frequency intervals given by Varsanyi [25, 26].
Methylene Group (CH2) Vibrations
In present molecule, two methylene groups are available, which are attached in Naringenin core and in D-glucose structure. In which, the methylene group in Naringenin core has observed at higher frequency than in ring D. The symmetric and asymmetric (H68-C5-H9) stretching modes are assigned to 2929 cm-1/FT-IR (2927/mode number: 189) and 3005 cm-1 (mode number: 197) respectively. Similarly, the harmonic bands 2865 cm-1 (mode number: 182) and 2904 (mode number: 187)/ 2899 cm-1: Raman are assigned to δCH2 (sym) and δCH2 (H57-C54-H58) (asym) mode respectively. These assignments are well comparable and also find support from TED column. The methylene group has six normal modes of vibrations, namely CH2 symmetric (νsym), CH2 asymmetric (νasym), scissoring (δ), rocking (ρ), wagging (ω) and twisting (t) modes are able to appear in the range 1500-800 cm-1 [22].

In this molecule, there are two CH2 groups (ring B & D). The general order of CH2 deformation is: CH2 scissoring > CH2 wagging > CH2 twisting > CH2 rocking. In the present study, the CH2 bending modes follow the same trend. Since the bending modes involving hydrogen atom attached to the central carbon fall into the range 1450-875 cm-1 there are extensive vibrational coupling of these modes with CH2 deformations particularly with the CH2 twist [26]. It is notable that both CH2 scissoring and CH2 rocking were sensitive to the molecular conformation. The mode numbers: 167, 174 are belonging to the δCH2 mode. The frequencies observed at 1185 cm-1 (FT-Raman) and at 1136 cm-1 (FT-IR) are assigned to CH2 wagging and CH2 twisting, respectively. The other fundamental mode of CH2 (rocking: mode number: 97) is observed in the expected region and also presented in Table 1. These assignments are found to be satisfactorily in agreement with the reported values [27].
O-H Vibrations
The broad, intense –OH stretching absorption from 3300 to 2500 cm-1 suggests the presence of carboxylic group in the Naringin extracted from kinnow peel. The strong and broad hydrogen bonded O-H stretching bands centering 3300 and 3400 cm-1 are for alcohols and phenols, respectively [28]. The hydroxyl group vibrations are appeared in the higher range than other vibrations. In our study, the O-H group stretching vibration of A, B, C, D and E rings are lies at different frequencies. In this molecule, the mode numbers: 213, 208, 207 and 211, 209, 206 are assigned to the ν(OH) for ring D and ring E, respectively. The harmonic values 3653 cm-1 (mode number: 210/ring A) and 3672 cm-1 (mode number: 212/ring C) are belong to the core molecule of Naringin. The experimental νOH group vibration has observed at 3427 cm-1 as a shoulder band in FT-IR spectrum, which is exactly matches with the literature value 3433 cm-1 [29].

The OH in-plane bending vibration appears in the range of 1440-1395 cm-1. Akkaya and Akyüz et al. assigned this vibration at 1294 and 1160 cm-1 in IR for 4-aminosalicylic acid [18, 30]. For 3-aminosalicylic acid, this band is observed at 1340 and 1171 cm-1 which is a motion of hydroxyl group [31]. In the present work, the O-H in-plane bending mode is assigned to 1393 cm-1 in FT-IR and 1254, 1185, 1122 cm-1 in FT-Raman experimentally, which are calculated at 1390, 1254, 1180, 1116 (mode numbers: 164, 139, 129, 122) for Naringin. The above assignments are supported by TED values. The δCOH and τCOH vibrations (harmonic) are calculated in the regions 1423-1153 cm-1 (mode numbers: 170- 126) and 774-228 cm-1 (mode numbers: 80-27), respectively. The observed bands 1215 (FT-Raman), 1263 cm-1(FT-IR) and
Table 1: The vibrational assignments of Naringin using Scaled Quantum Mechanics method (B3LYP/6-31G(d,p)).

Scaled
B3LYPa

FT-IR

FT-Raman

IbIR

IcRaman

Vibrational assignments
TEDd  (≥ 10)

82

 

86s

0.37

1.09

τcccc(16)+ Γoccc(13)

132

 

140w

0.14

2.02

τccco(10)

169

 

168w

0.50

1.30

δccc(15)

220

 

220w

1.31

0.59

δC45-C44-C69(14) +τHCCC (10)

240

 

247w

8.53

3.46

τH56-O55-C54-C32(32)+ τH56-O55-C54-H57(22)+ τH56-O55-C54-H58(11)

376

 

385w

0.98

0.86

δOCC (10)

435

434w

 

5.92

0.45

τHCCC(10)

446

 

448w

4.02

0.95

δCCO(10)

476

 

469w

0.41

0.41

δCCO(10)

481

481w

 

1.63

1.09

τCCOC(11)+ τHOCC(12)  

514

511w

 

0.30

0.99

δCOC(14)

523

522w

520w

3.30

3.07

νCC(10)+νOC(10)+ τHOCC(22)+τHOCH(10)

548

 

563w

1.26

1.93

νCC(10)

576

561w

 

0.31

0.67

δOCC(13)

597

 

 

2.97

1.77

δOCC(11)

605

608w

607w

2.01

0.48

τHCCC(10)

616

 

 

1.10

4.59

τCCCC(10)+ τCCCH(10)

621

626w

 

0.97

0.15

τCCCC(12)+ τOCCC(10)

630

637w

 

1.21

2.15

δCCC(35)

642

 

643w

0.81

3.90

νCC(16)

661

 

663ms

0.30

0.67

δCOC(12)

666

668w

 

4.51

0.24

τCCOC(14)

700

702w

704w

7.31

0.71

τH37-O36-C33-C31(10)

718

730w

 

0.23

0.55

τCCCC(31)+ τOCCC(21)

752

743w

748w

14.50

0.21

τH49-O48-C42-C41(30)+ τH49-O48-C42-C43(27)+ τH49-O48-C42-H63(14)

812

 

812w

6.63

0.48

τC24-C22-C19-H23(13)+ τH26-C22-C19-C17(17)+ τO27-C24-C22-H26(21)

823

821ms

 

5.97

0.24

νCC(17)+ νOC(11)

848

835w

837w

1.61

2.71

νC18-C17(11)

871

864vw

864w

0.45

1.47

νC43-C42(15)

876

888w

 

2.61

0.89

νO13-C1(16)

910

 

896ms

0.22

0.34

τH21-C18-C17-C1(15)+ τC24-C20-C18-H21(11)+τH25-C20-C18-H21(35)

922

919w

 

0.01

0.12

τH23-C19-C17-C1(12)+ τH23-C19-C17-C18(11)+ τH26-C22-C19-H23(36)

987

986ms

982w

28.45

4.40

νO35-C29(20)

990

 

1002w

3.25

0.12

νCC(31)+δCCC(32)+δCCH(18)+δHCC(14)

1039

 

1039w

15.09

0.88

νC5-C1(14)+νC33-C32(14)

1040

1040s

 

3.50

3.12

νC5-C1(19)+νO13-C1(11)

1063

1060s

 

33.94

1.22

νO13-C2(12)+νO15-C8(11)+νO55-C54(19)

1076

1071s

 

7.75

0.30

νO36-C33(19)

1082

 

1081ms

25.65

1.70

νO38-C31(15)+νC41-O40(11)+νO48-C42(11)

1087

1089s

 

1.36

0.95

νC22-C19(15)+δH26-C22-C19(14)

1116

 

1122ms

8.29

0.35

δH53-O52-C45(11) +ΓHCCH(10)

1134

1136s

 

17.14

0.89

νO46-C41(15) +δCCH(10)

1175

1178s

 

2.39

0.59

νC10-C8(11)+δH12-C10-C8(13)+δH16-O15-C8(36)

1180

 

1185w

3.80

1.01

δH56-O55-C54 (24)+δCCH(10)+δH37-O36-C33(10)

1203

1205s

1210s

12.61

4.78

νC4-C3(10)

1217

 

1215w

3.99

0.92

δH56-O55-C54(23)+δH58-C54-C32(12)+δO55-C54-H58(10)

1254

 

1254w

41.32

6.38

νC4-C3(18)+δH16-O15-C8(19)

1260

1263w

 

0.21

0.44

δHOC(14)

1284

1282w

 

5.76

0.62

νC18-C17(12)

1297

1296s

 

1.93

1.15

νC45-C44(11)+ δO46-C44-H60 (11)     

1344

1341ms

 

7.17

1.37

δOCC(10)

1349

 

1348ms

1.73

0.32

δHCC(13)+ΓHCCH (11)

1363

1363ms

 

1.88

0.30

δH71-C69-H72(20)+δHCC(18)

1370

 

1373w

0.57

0.51

δO34-C29-H67(12)+ ΓH59-C30-C29-H67(11)

1390

1393ms

 

12.51

0.24

δH39-O38-C31(33)

1450

1453ms

1456ms

0.08

1.04

δH70-C69-H72(39) +ΓHCCH(10)

1502

1502ms

1502vw

12.45

0.71

νC18-C17(10)

1561

 

1574ms

20.70

0.96

νC3-C2(12)+νC8-C3(13)+νC11-C7(12)+νC11-C10(28)

1584

1582ms

 

3.29

0.61

νC18-C17(11)+νC19-C17(20)+νC24-C20(20)+νC24-C22(17)

1710

1646s

1643vs

36.22

7.18

νO14-C4(87)

2888

2890w

 

3.24

1.62

νC1-H73(97)

2904

 

2899ms

4.31

1.64

νC54-H57(28)+νC54-H58(69)

2927

2929w

 

1.27

1.28

νC5-H9(87)+νC5-H68(11)

2939

 

2939w

2.77

0.78

νC29-H67(97)

2952

 

2958w

1.95

0.98

νC31-H64(23)+νC33-H65(55)+νC32-H66(21)

2985

2970w

2976w

2.17

1.36

νC30-H59(95)

3083

 

3071w

0.88

0.96

νC18-H21(95)

3425

3427s

 

69.82

1.75

νO48-H49(95)

v: Stretching, δ: In-plane-bending, τ: Out-of-plane bending, vw: very weak, m: medium, s: Strong, vs: very strong, aScaled computed wavenumber using scale factor: 0.9608 (palafox, 2000),
b Relative IR Absorption intensities normalized with highest peak absorption equal to 100,
c Relative raman intensities calculated by equation (2.1) and normalized to 100.
d Total energy distribution calculated at B3LYP/6-31G(d,p) level.
743/748 cm-1 (FT-IR/FT-Raman), 247 cm-1: FT-Raman supports the above assignments.
C=O and C-O Vibrations
Normal esters are characterized by strong IR absorption due to the carbonyl (C=O) stretching vibration in the range 1750-1735 cm-1 [32]. The FT-IR and FT-Raman spectra show the vibrational frequency for C=O at 1646 cm-1 and 1633 cm-1 respectively [33, 29]. The presence of carbonyl group on Naringin can be confirmed from peak situated at 1634 cm-1 [34]. The carbonyl stretching vibration observed as an intense band at 1603 cm-1 for 6-aminoflavone in FT-IR. The observed wavenumber of the carbonyl stretching vibration is lower due to π-electron being localized [22]. In the present study the C4=O14 stretching vibrations is appeared at 1646 (strong) and 1643 cm-1 (very strong) band in FT-IR and FT-Raman spectra respectively, while the harmonic value is 1710 cm-1 (mode number: 181).

In 2, 6-dichloro-4-nitrophenol, the νC-O vibrations lie in the region 1095-1310 cm-1 [35]. In our study, the νC-O vibrations are observed at different frequencies in different rings (A, B, C, D & E). The computed wavenumbers in the range 1354-1053 cm-1 (mode numbers: 158, 141, 124, 123, 121, 119, 118, 116-110) are assigned to νC-O mode. These vibrations have considerable TED and also find support from 1136, 1071, 1060 cm-1 (FT-IR) and 1081 cm-1 (FT-Raman). In ring B, the νO13-C2 is observed at higher frequency (1060 cm-1: FT-IR/1063: mode number: 111) than the νO13-C1 (1040 cm-1: FT-IR/1040: mode number: 109). The harmonic values C41-O46:1053 cm-1/mode number: 110 and C32-O34:814 cm-1/mode number: 87 are belongs to ring E and ring D, respectively.

Similarly the computed values 1066 cm-1/mode number: 112, 1038 cm-1/mode number: 107 and 987 cm-1/mode number: 100 are belongs to C54-O55, C30-O40 and C29-O35 stretching vibrations, respectively.
C-C Vibrations
The ring C-C stretching occurs in the region 1625-1430 cm-1. The six member aromatic ring has two or three strong bands in the region about 1500 cm-1 are being due to skeletal vibration [33]. The C-C stretching bands for aromatic ring usually appear between 1600 and 1450 cm-1. The C-C stretching of alkenes appeared at 1650 cm-1 [36, 29]. In the present study, the FT-IR bands at 1582, 1502 (in ring C), and FT-Raman bands at 1574 (ring A), 1502 cm-1 (in ring C) are assigned to νC-C mode. The calculated νC-C frequencies are in the range 1610-1473 cm-1 using B3LYP/6- 31G (d, p) level. In which the mode numbers: 179, 177, 175 and 180, 178, 176 are belongs to ring A and ring C, respectively. The harmonic vibrations 1297 (ring E), 1284 (ring C), 1254 (ring B), 1203 (ring B), 1175 (ring A), 1087 (ring C), 1040 (ring B), 1039 (ring D), 1032 cm-1 (ring D) are also attributed to νC-C mode. These assignments are supported by 1296, 1282, 1205, 1178, 1089, 1040 cm-1 (FT-IR) and 1254, 1210 1039 cm-1 (FT-Raman) observed bands and also have considerable TED values. The νC-C vibrations (other than ring) 1191 cm-1/mode no: 131, 1104 cm-1/ mode no: 120 and 1025 cm-1/mode no: 105 are belongs to C17-C1, C54-C32 and C69-C44, respectively.

In-plane bending deformation δHCC and δCCH are observed at 1348 (FT-Raman), 1215 (FT-Raman), 1178 (FT-IR), 1089 (FTIR) and 1002 cm-1 (FT-Raman) respectively. The observed FT-IR bands: 919, 608, 434 cm-1/Raman: 896, 812, 607 cm-1 and FTRaman bands: 896, 812 cm-1 are assigned to τHCC and τCCH modes, respectively. Erdoğdu et al., observed the δCCH mode in the region 1495-1001 cm-1 and τCCH mode in the region (FT-IR) 923-451 cm-1 for 6,8-dichloroflavone [33]. The ring breathing mode was calculated at 990 cm-1/ mode number: 101 for Naringin and was observed at 1002 cm-1 in Raman spectra. These assignments are in line with literature [33].
NBO Analysis
The hyperconjugation may be given as stabilizing effect that arises from an overlap between an occupied orbital with another neighboring electron deficient orbital, when these orbitals are properly orientated. This non-covalent bonding-antibonding interaction can be quantitatively described in terms of the NBO analysis, which is expressed by means of the second-order perturbation interaction energy (E(2)) [37-40][46-49]. This energy represents the estimate of the off-diagonal NBO Fock matrix elements. It can be deduced from the second-order perturbation approach [41]
E (2) =ΔE ij =q i F(i,j) 2 ε j -ε i       (2) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcaaMaaeyraO WaaWbaaKqaGfqabaGaaeikaiaabkdacaqGPaaaaKaaGjaab2dacaqG uoGaaeyraOWaaSbaaKqaGfaacaqGPbGaaeOAaaqabaqcaaMaaeypai aabghakmaaBaaajeaybaGaaeyAaaqabaGcdaWcaaqcaawaaiaabAea caqGOaGaaeyAaiaabYcacaqGQbGaaeykaOWaaWbaaKqaGfqabaGaae OmaaaaaKaaGfaacaqG1oGcdaWgaaqcbawaaiaabQgaaeqaaKaaGjaa b2cacaqG1oGcdaWgaaqcbawaaiaabMgaaeqaaaaakiaabccacaqGGa GaaeiiaiaabccacaqGGaGaaeiiaiaabIcacaqGYaGaaeykaaaa@5638@
where qi is the donor orbital occupancy, εi and εj are diagonal elements (orbital energies) and F (i, j) is the off diagonal NBO Fock matrix elements.

The NBO analysis has been carried out to elucidate the intra-molecular interaction among natural bond orbitals, the results of NBO analysis are presented in Table 2. In the present investigation, the π- π* interaction are mainly interested. Here the electron densities of conjugated π bonds are lower than the σ bond. Whereas, the delocalization is more while the transition from π bond to π* bond. The larger E(2) value, denotes that the more delocalization takes place into a particular bond, it mainly occurs during π-π* transition. Moreover, as mentioned above the electron densities in donor (i) π bonds decreases, at the same time electron density increases in acceptor (j) π* bonds. It is evident from the Table 2 the donor (π) bonds have 1.678, 1.621, 1.667, 1.702 and 1.652e as electron densities for C2-C7, C3-C8, C17-C18, C19-C22 & C20-C24 bond, respectively. These electron densities are relatively lesser than the σ bonds. On the other hand, the strong delocalization occurs between donor (π: C2-C7, C3-C8, C17-C18, C19-C22 and C20-C24 bonds) and acceptor ( π*: C3-C8, C2-C7, C19-C22, C17-C18 and C17-C18 bonds) bonds, and the electron densities relatively increased in acceptor bonds and hence leading to more stabilization energies are obtained as 51.46, 126.44, 96.23, 75.02 and 94.73 kJ/mol, respectively. The NBO analysis explores the insights of intra molecular interactions among the intra bonds in Naringin molecule.
Table 2: Second order perturbation theory analysis of Fock matrix in NBO basis for Naringin using B3LYP/6-31G(d,p) basis set.

Type

Donor (i)

ED/e

Acceptor (j)

ED/e

E(2)
kJ/mola

π-π*

C2-C7(2)

1.678

C3-C8(2)

0.468

51.46

 

 

 

C10 –C11(2)

0.429

121.92

π-π*

C3-C8(2)

1.621

C2-C7(2)

0.387

126.44

 

 

 

C4-O14(2)

0.159

92.05

 

 

 

C10-C11(2)

0.429

54.56

π-π*

C10 – C11(2)

1.973

C2-C7(2)

0.387

52.51

 

 

 

C3-C8(2)

0.468

122.47

π-π*

C17-C18(2)

1.667

C19-C22(2)

0.335

96.23

 

 

 

C20-C24(2)

0.394

75.56

π-π*

C19-C22(2)

1.702

C17-C18(2)

0.361

75.02

 

 

 

C20-C24(2)

0.394

95.60

π-π*

C20-C24(2)

1.652

C17-C18(2)

0.361

94.73

 

 

 

C19-C22(2)

0.335

71.96

n- π *

LPO13(2)

1.837

C2-C7(2)

0.387

121.84

n- σ*

LPO14(2)

1.877

C3-C4

0.071

100.17

 

 

 

C4-C5

0.064

95.90

n- π *

LPO15(2)

1.838

C3 –C8(2)

0.468

152.30

n- π *

LPO27(2)

1.869

C20-C24(2)

0.394

127.32

n- π *

LPO34(2)

1.895

C29-O35

0.064

68.87

n- π *

LPO35(2)

1.827

C10-C11(2)

0.429

121.17

 

 

 

C29-O34

0.059

54.10

 

 

 

C29-H67

0.031

18.16

n- σ*

LPO36(2)

1.930

C31-C33

0.051

28.58

 

 

 

C32-C33

0.046

26.07

 

 

 

O38-H39

0.025

18.16

n- σ*

LPO38

1.972

C31-C33

0.051

12.30

n- σ*

LPO38(2)

1.937

C30-C31

0.044

26.57

 

 

 

C31-H64

0.026

10.96

 

 

 

O48-H49

0.029

32.13

n- σ*

LPO40(1)

1.949

C30-H59

0.025

13.18

 

 

 

O36-H37

0.019

12.59

 

 

 

C41-O46

0.041

11.25

 

 

 

C41-H47

0.044

13.93

n- σ*

LPO40(2)

1.913

C29-C30

0.059

35.56

 

 

 

C41-C42

0.064

28.70

 

 

 

C41-O46

0.041

18.45

n- σ*

LPO46

1.949

O40-C41

0.048

15.82

 

 

 

C41-C42

0.064

16.48

 

 

 

C44-C45

0.038

14.77

n- σ*

LPO46(2)

1.914

O40-C41

0.048

14.39

 

 

 

C41-C42

0.064

11.51

 

 

 

C41-H47

0.044

36.36

 

 

 

C44-H60

0.025

10.50

 

 

 

C44-C69

0.026

24.81

n- σ*

LPO48

1.970

C42-H63

0.030

13.89

 

 

 

O50-H51

0.016

11.59

n- σ*

LPO48(2)

1.947

C41-C42

0.064

39.83

 

 

 

C42-H63

0.030

12.72

n- σ*

LPO50

1.974

C42-C43

0.048

8.74

n- σ*

LPO50(2)

1.952

C42-C43

0.048

24.06

 

 

 

C43-H62

0.034

30.88

 

 

 

C43-C45

0.046

32.51

 

 

 

C45-H61

0.032

24.23

 

 

 

C54-H57

0.030

29.66

 

 

 

C54-H58

0.026

27.07

π*-π*

C3-C8*(2)

0.468

C-O14*(2)

0.160

481.33

π*-π*

C20-C24*(2)

0.394

C17-C18*(2)

0.361

1107.92
aE(2) means energy of hyper conjugative interaction (stabilization energy, converted as 1kcal/mol=4.18kJ/mol),
Hyperpolarizability calculations
The first hyperpolarizabilities (β0) polarizability (α0) and dipole moment (μ) of Naringin molecule has calculated by B3LYP level of theory using 6-31G (d, p) basis set, based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [42]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3x3x3matrix is a tetrahedral. The components of β are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes:
E=E 0 -μ α F α -1/2α αβ F α F β -1/6β αβγ F α F β F γ     (3) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcaaMaaeyrai aab2dacaqGfbGcdaahaaqcbawabeaacaqGWaaaaKaaGjaab2cacaqG 8oGcdaWgaaqcbawaaiaabg7aaeqaaKaaGjaabAeakmaaBaaajeayba GaaeySdaqabaqcaaMaaeylaiaabgdacaqGVaGaaeOmaiaabg7akmaa BaaajeaybaGaaeySdiaabk7aaeqaaKaaGjaabAeakmaaBaaajeayba GaaeySdaqabaqcaaMaaeOraOWaaSbaaKqaGfaacaqGYoaabeaajaay caqGTaGaaeymaiaab+cacaqG2aGaaeOSdOWaaSbaaKqaGfaacaqGXo GaaeOSdiaabo7aaeqaaKaaGjaabAeakmaaBaaajeaybaGaaeySdaqa baqcaaMaaeOraOWaaSbaaKqaGfaacaqGYoaabeaajaaycaqGgbGcda Wgaaqcbawaaiaabo7aaeqaaOGaaeiiaiaabccacaqGGaGaaeiiaiaa bIcacaqGZaGaaeykaaaa@64D5@
where E0 is the energy of the unperturbed molecules, Fα is the field at the origin, and μ α ,α αβ ,β αβγ MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKaaGjaabY7akm aaBaaajeaybaGaaeySdaqabaqcaaMaaeilaiaabg7akmaaBaaajeay baGaaeySdiaabk7aaeqaaKaaGjaabYcacaqGYoGcdaWgaaqcbawaai aabg7acaqGYoGaae4Sdaqabaaaaa@4541@ is the components of the dipole moment, polarizability and the first hyperpolarizability, respectively. The total static dipole moment μ, the mean polarizability α0, the anisotropy of polarizability Δα and the mean first hyperpolarizability β0, using the x, y, z components are defined as
μ=(μ x 2 +μ y 2 +μ z 2 ) 1/2      (4) α 0 = α xx +α yy +α zz 3      (5) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajaayca qG8oGaaeypaiaabIcacaqG8oGcdaqhaaqcbawaaiaadIhaaeaacaqG YaaaaKaaGjaabUcacaqG8oGcdaqhaaqcbawaaiaadMhaaeaacaqGYa aaaKaaGjaabUcacaqG8oGcdaqhaaqcbawaaiaadQhaaeaacaqGYaaa aKaaGjaabMcakmaaCaaajeaybeqaaiaabgdacaqGVaGaaeOmaaaaki aabccacaqGGaGaaeiiaiaabccacaqGGaGaaeikaiaabsdacaqGPaaa baqcaaMaaeySdOWaaSbaaKqaGfaacaWGWaaabeaajaaycaqG9aGcda Wcaaqcaawaaiaabg7akmaaBaaajeaybaGaamiEaiaadIhaaeqaaKaa GjaabUcacaqGXoGcdaWgaaqcbawaaiaadMhacaWG5baabeaajaayca qGRaGaaeySdOWaaSbaaKqaGfaacaWG6bGaamOEaaqabaaajaaybaGa ae4maaaakiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeikaiaabw dacaqGPaaaaaa@6771@ Δα=2 -1/2 [ ( α xx -α yy ) 2 + ( α yy -α zz ) 2 + ( α zz -α xx ) 2 +6( α xy 2 +α yz 2 +α xz 2 ) ] 1/2    (6) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeiLdiaabg 7acaqG9aGaaeOmamaaCaaaleqabaGaaeylaiaabgdacaqGVaGaaeOm aaaakmaadmaabaWaaeWaaeaacaqGXoWaaSbaaSqaaiaadIhacaWG4b aabeaakiaab2cacaqGXoWaaSbaaSqaaiaadMhacaWG5baabeaaaOGa ayjkaiaawMcaamaaCaaaleqabaGaaeOmaaaakiaabUcadaqadaqaai aabg7adaWgaaWcbaGaamyEaiaadMhaaeqaaOGaaeylaiaabg7adaWg aaWcbaGaamOEaiaadQhaaeqaaaGccaGLOaGaayzkaaWaaWbaaSqabe aacaqGYaaaaOGaae4kamaabmaabaGaaeySdmaaBaaaleaacaWG6bGa amOEaaqabaGccaqGTaGaaeySdmaaBaaaleaacaWG4bGaamiEaaqaba aakiaawIcacaGLPaaadaahaaWcbeqaaiaabkdaaaGccaqGRaGaaeOn amaabmaabaGaaeySdmaaDaaaleaacaWG4bGaamyEaaqaaiaabkdaaa GccaqGRaGaaeySdmaaDaaaleaacaWG5bGaamOEaaqaaiaabkdaaaGc caqGRaGaaeySdmaaDaaaleaacaWG4bGaamOEaaqaaiaabkdaaaaaki aawIcacaGLPaaaaiaawUfacaGLDbaadaahaaWcbeqaaiaabgdacaqG VaGaaeOmaaaakiaabccacaqGGaGaaeiiaiaabIcacaqG2aGaaeykaa aa@74E4@ β 0 = ( β x 2 +β y 2 +β z 2 ) 1/2    (7) MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKaaGjaabk7akm aaBaaajeaybaGaamimaaqabaqcaaMaaeypaOWaaeWaaKaaGfaacaqG YoGcdaqhaaqcbawaaiaadIhaaeaacaqGYaaaaKaaGjaabUcacaqGYo GcdaqhaaqcbawaaiaadMhaaeaacaqGYaaaaKaaGjaabUcacaqGYoGc daqhaaqcbawaaiaadQhaaeaacaqGYaaaaaqcaaMaayjkaiaawMcaaO WaaWbaaKqaGfqabaGaaeymaiaab+cacaqGYaaaaOGaaeiiaiaabcca caqGGaGaaeikaiaabEdacaqGPaaaaa@4FC9@
Many organic molecules, containing conjugated π electrons are characterized by large values of molecular first hyper polarizabilities, were analyzed by means of vibrational spectroscopy [43-46]. The intra molecular charge transfer from the donor to acceptor group through a single-double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making IR and Raman activity strong at the same time [47].

Table 3 lists the computed dipole moment (μ), polarizability (α) and first order hyperpolarizability (β0) as, 1.832 Debye, 0.840 x 10-30 esu and 6.477 x 10-30 esu, respectively. The first hyperpolarizability (β0) of the title molecule is fifteen times higher than that of urea; hence this molecule has considerable NLO activity. In this molecule, the π-π* interaction plays a major role in intra-molecular charge transfer and hence the hyperpolarizability of the molecule being increased.
UV-Visible Spectral Studies and HOMO-LUMO Analysis
The ultraviolet absorption spectrum was obtained in the range of 200-500 nm to study the electronic properties of Naringin. The UV pattern was taken from a 10-5 molar solution of Naringin dissolved in methanol. TD-DFT calculation was performed to examine the electronic excitations within the MOs
Table 3: The electric dipole moments (μ), polarizability (α) and hyperpolarizability (β0) values of Naringin.

Parameters

B3LYP/6-31G(d,p)

             Dipole moment ( μ )                                                    Debye

μx

-1.774

μy

-0.165

μz

0.423

μ

1.832

              Polarizability ( α )                                                  x10-30 esu

αxx

396.795

αxy

-40.462

αyy

362.008

αxz

6.148

αyz

18.176

αzz

246.065

α

0.840

         Hyperpolarizability  ( β0)x10-30 esu

βxxx

-790.564

βxxy

-511.101

βxyy

210.872

βyyy

49.444

βxxz

-84.623

βxyz

50.617

βyyz

-14.420

βxzz

4.864

βyzz

-8.700

βzzz

-2.629

β0

6.477

Standard value for urea (μ=1.3732 Debye, β0=0.3728x10-30 esu)
of Naringin. The both experimental UV and computed results are listed in Table 4. In this work the observed band gaps are about 328.00, 282.60, 279.80 nm and computed band gap are about 344.74, 293.04, 279.63 nm. These values clearly denote that the excitation lay among the conjugative bonds. The Figure 4 shows the absorption spectrum (in methanol) of Naringin. The frontier molecular orbitals are shown in Figure S1 (Supplementary information). The HOMO is located over the 2px orbitals of carbon and oxygen atom in ring D, E and LUMO states appears in ring A. In addition to that the neighboring HOMO-1,-2,-3 and LUMO+1, +2+3 are also shown in Figure S1. The estimated HOMO energy is -5.869 eV, and LUMO energy is -1.034 eV and the HOMO-LUMO energy gap is -4.835 eV.
Summary and Conclusion
In the present investigation we investigate the structural, spectral and molecular orbitals (MO’s) properties of naringin. Naringin consists of naringenin (ring A-C), D-glucose (ring D) and L-rhamnose (ring E). The molecular geometry was studied and found the intra molecular hydrogen bonding between carbonyl and hydroxyl group (C4=O14 ...H16-O15). Vibrational behavior of Naringin was studied by FT-IR and FT-Raman spectra, these spectral values were compared with computed vibrational wavenumbers, agreement is good and discussed the discrepancies among wavenumbers. Furthermore, inter and intra molecular charge transfers were measured by NBO analysis, it clear showed the maximum energy exchange occurs among π-π* interactions. The calculated first order hyperpolarizability (6.477x10-30 esu) is fifteen times higher than that of urea; hence this molecule has a considerable nonlinear optical property. The obtained UV spectrum show excitations at 328.00, 282.60, 279.80 nm, it clearly denote the excitation lay among the conjugative bonds and calculated HOMO is located over the 2px orbitals of carbon and oxygen atom in ring D, E and LUMO states appears in ring A, whereas, the band gap energy is estimated at -4.835 eV.
Table 4: The electronic transition of Naringin using TD-B3LYP/6-31G(d,p) level.

Calculated at B3LYP/
6-31G(d,p)

Oscillator strength

Experimental
 Band gap (nm)

 Calculated
Band gap (eV/nm)

Excited state 1

Singlet-A/f=0.0010

328.00

3.5964 eV /344.74nm

151->154 (HOMO-2-LUMO)

 

 

-5.203

153->154 (HOMO- LUMO)

 

 

-4.835

Excited State   2

Singlet-A /f=0.0499

282.60

4.2310 eV  /293.04 nm 

150 ->154(HOMO-3- LUMO)  

 

 

-5.263

150 ->156(HOMO-3- LUMO+2)

 

 

-6.153

150 ->157(HOMO-3- LUMO+3 

 

 

-5.939

152 ->154(HOMO-1-LUMO

 

 

-4.917

153 ->154(HOMO-LUMO

 

 

-4.835

Excited State   3

Singlet-A/ f=0.0252     

279.80

4.4338 eV   /279.63 nm 

151 ->154(HOMO-2- LUMO)  

 

 

-5.203

152 ->154(HOMO-1-LUMO)

 

 

-4.917

153 ->154(HOMO-LUMO)  

 

 

-4.835

Figure S1: The Frontier molecular orbitals of Naringin.
Figure 4: The UV-Visible spectrum is taken from a 10-5 molar solution of Naringin dissolved in methanol.
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