CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.11 No.06, pp 145-159, 2018
Abstract : The Fourier transform infrared and FT-Raman spectra of -acetyl--butyrolactone have been recorded in region 4,000–400 and 4,000–100 cm -1 respectively. A complete assignment and analysis of fundamental vibration modes of the molecule have been carried out. The observed fundamental modes have been compared with harmonic vibration frequencies computed using density functional theory calculations by employing B3LYP functional at 6-311+G(d,p) level. UV–Visible spectrum of the compound has been recorded and electronic properties, such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been calculated with B3LYP/6311++G(d,p) level. These calculated energies show that charge transfer occurs within molecule. Mulliken population analysis and thermodynamic properties of title compound have also been calculated. Keywords : -acetyl--butyrolactone, DFT, HF, FT-IR, FT-RAMAN, UV, HOMO-LUMO.
K.Rajalakshmi et al /International Journal of ChemTech Research, 2018,11(06): 145-159.
DOI= http://dx.doi.org/10.20902/IJCTR.2018.110620
The present investigation was undertaken to study the vibrational spectra of – acetyl -– butyrolactone to identify the molecular structure and properties with support of FT-IR and FT-Raman experimental spectral data compared to that of theoretical observed data by using DFT/B3LYP/6-311+G(d,p) and HF/6-311+G(d,p). The electronic transition in UV-Vis spectra also analyzed for the molecule. The HOMOLUMO analysis, Mulliken charge distribution and thermodynamic properties were obtained theoretically form the harmonic vibrations.
The aim of this work is to investigate the molecular structure, vibrational study of the molecule due to its biochemical importance. To the best our knowledge, no work on vibrational assignments, molecular structure and stability have been reported earlier.
The pure sample was purchased from Avra synthesis India Pvt. Ltd., with started purity 98% and was used as such without further purification.
The Fourier transform infrared spectrum of the title compound was carried out with anIR affinity model Shimadzu FT-IR spectrometer with a room temperature DLATGS detector. The spectra of the solids were
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recorded in technique of KBr pellets in the 4000-400cmspectral region at 4 cm spectral resolution accumulating 32 scans.
The Fourier transform Raman spectrum was carried out with a Bruker IFS 66V FT-Raman spectrometer equipped with FRA-106 and 1064 nm line of Nd: YAG laser was used for excitation wavelength in the region 4000-50 cm-1 and 200 mW output powers. The reported wave numbers are expected to be accurate within 1 cm-1. The FTIR, FT-Raman spectrums are presented in the Fig 3 and Fig.4 respectively.
The Ultraviolet-Visible spectrum was recorded in the range of 200-800nm using with Jasco V-670 spectrometer. The Spectral measurement was carried out by the spectrometer. The response fast scans speed 2000 nm/min with using light source D2/WI.
Quantum chemical calculation were carried out with GAUSSION suite of 09W program package on personal computer [4] using Ab initio HarteeFock (HF) and density functional theory (DFT) employing the Becke's Three-parameters hybrid functional[5] combined with Lee-Yang-Parr correction [6] functional (B3LYP) methods has been implemented with 6-311+G(d,p) basis sets. In the present study, the molecular geometry optimizations, vibrational frequency with intensity calculations and other molecular properties of Mulliken charge analysis, thermodynamic properties were carried out by using HF/6-311+G(d,p) and DFT/B3LYP/6-311+G(d,p). The vibrational frequencies are scaled down by the appropriate scaling factor [7] thereby the vibrational assignment are compared with observed values and HOMO-LUMO analysis were calculated by using DFT/B3LYP/6-311+G(d,p).
The – acetyl -– butyrolactone (C6H8O3) molecular structure is shown in the Fig 1. This molecule containing 17 (6 carbon, 8 hydrogen and 3 oxygen) atoms and its molecular weight is 128.127 g/mol.
Fig 1 Molecular structure for – acetyl -– butyrolactone
The optimized structure parameters of ABL calculated by HF and DFT/B3LYP levels with 6311+G(d,p) basis sets are listed in the Table 1in accordance with the atom numbering scheme given in Fig. 2. In the table compares the calculated bond angles and bond lengths with experimental data.
The calculated bond length (C=O) of O2 –C7 in B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) are 1.2007 A0 and 1.1969 A0 respectively which are in good agreement with experimental value 1.2213. Also bond length (C=O) of O3 – C8 in B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) are found be 1.2093 A0 and 1.1862 A0which are in good agreement with experimental value 1.2300 A0. The bond lengths (C-O) of O1-C6 and O1 -C7 are
0 00 0
found to be 1.4483 A(B3LYP), 1.4223 A(HF) and 1.3517 A(B3LYP), 1.3232 A(HF) respectively which are in good agreement with experimental values 1.4311 A0 and 1.3688 A0.
Fig 2. Molecular structure with Atom numbering for – acetyl – butyrolactone
These calculated and experimental values of double bond (C=O) and single bond (C-O) lengths are indicating that its involvement of conjugation [8] and also the small difference between C-O bond lengths of O1 -C7and O1-C6 can be attributed to the conjugation of the -butyrolactone ring and presence of C-H group in the neighboring position [9]. The O-C-C bond angles ofO1-C6-C5=105.7405and O3-C8-C9=120.5056in B3LYP/6-311+G(d,p), which are shows interaction between Hydrogen and Oxygen atoms [10]. The CH group bond length are in the range of literature 1.0958-1.1119 A0 for CH2 and CH3 groups, the C-H bond lengths are in the range of 1.0918-1.0951 A0 [11]. All the CH bonds in our title molecule (CH2, CH3 and C-H) are good agreement with the experimental and literature values.
It is seen that, the C-C bond length of our title molecule are C4-C5= 1.5282 A0 and C5-C6=1.5325 A0 (B3LYP/6-311+G(d,p)) due to the presence of five atoms in the ring, which is slightly higher when compared to six membered benzene ring (C-C=1.40 A0). Similarly, in our title molecule the bond angle of C-C-C is reduced by 103.03540 (C4-C5-C6), when compared bond angle to benzene ring (C-C-C=1200).
The title compound, ABL consists of 17 atoms with 3N degrees of freedom corresponding to the Cartesian coordinates of each atom in the molecule. In a non linear molecule, 3 of these degrees belong to the rotational, 3 of these degrees belong to translational motions and remaining (3N-6) corresponds to its vibrational motions [12]. Therefore the net number of modes of vibrations is 45. The detailed vibrational analysis of fundamental modes using HF/6-311+G(d,p) and DFT/6-311+G(d,p) with FT-IR and FT-Raman experimental frequencies of title molecule were presented in Table 2.
The calculated vibrational wave numbers are usually higher than the corresponding experimental quantities because of the combination of electron correlation effects and basis sets deficiencies [38]. Therefore, an empirical uniform scaling factor was used to offset the systematic errors caused by basis set incompleteness of electron correlation and vibrational anharmonicity. For DFT/B3LYP and HF levels with 6-311+G(d,p) basis set, the wave numbers are scaled with 0.95 and 0.91 respectively.
To understand at molecular level, both empirical and quantum chemistry calculations have been widely used in molecular modeling. Empirical approach uses simple models of harmonic potential, electrostatic interaction, and dispersion forces, allow for basic comparisons of energetic and geometry optimization. While quantum chemistry approaches based on explicit consideration of the electronic structure can be either Ab initio or semi empirical parameterized. In case of semi empirical model, some quantities can be taken from experiment or estimated by fitting to the data. Additionally, density functional method using electron density as a primary way of describing the system can also be used. In general, semi empirical density functional approximations were mostly used.
Lactone shows two characteristic intense bands arising from C=O and C – O stretching modes and ketones are best characterized by the strong C=O stretching vibrations [13]. Their vibrations spread over a large range of wavenumber. Lactone and other ring are also found in several different substance of biological interest[14].
The intense of C=O stretching vibration appears at higher frequency than that of normal ketones. The carbonyl stretching vibrations in ketones are expected in the region 1680-1715cm-1 and -butyrolactone (fivemembered ring) are expected in the region 1795-1760cm-1 [15].
Accordingly, in the present study the very strong intense bands in FT-IR spectrum at 1762 and 1713cm 1, which is also observed weak intense bands in FT-Raman spectrum at 1763 and 1719cm-1.The theoretical calculation of B3LYP/6-31+G(d,p) method gives the C=O stretching vibration at 1749 and 1706cm-1 and HF/6311+G(d,p) gives at 1840 and 1810cm-1 .
K.Rajalakshmi et al /International Journal of ChemTech Research, 2018,11(06): 145-159. | 149 | ||||||||||
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Table | 1 | Optimized | Geometrical | parameters | (bond length (A0), | bond | angels (0)) | of | – | acetyl | – |
butyrolactone |
The higher IR frequency at 1762 was assigned to C7-O1 stretching. The vibration frequency of ketone carbonyl group C8-O3 assigned at 1713 cm-1, which is lower than that of C7-O1bond due to its different position in the molecule. The C7-O1 band has in gamma position atom O1 and belongs to the Lactone group; therefore its frequency is higher than the frequency of the ketone carbonyl group C8-O3.[16] The position of the C=O stretching vibration is very sensitive to various factors such as the physical state, electronic effects by substituent, ring strains,[17] etc.
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The out of plane bending modes of C=O bonds are observed at 588,465cmin FT-IR and 453 cmin
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Raman; 567, 442, 58 cmin B3LYP/6-311+G(d,p) and 586, 461, 53 cmin HF/6-311+G(d,p).
4.3.3C – O Vibration
In the C – O stretching region, lactones shows a strong C – O stretching band where as a weaker band occurs for ketone. The 1200-950 cm-1 regions are the C – O stretching region with contribution of C-C vibration [18].
In the present study the very strong bands occurring at 1148 and 1001cm-1 in FTIR spectra are assigned to C – O stretching, and also observed very weak band in Raman spectra at 965 cm -1.The theoretically computed frequencies for C – O stretching vibration at 1104 and 998 cm-1 by B3LYP/6-311+G(d, p) and HF/6311+G(d,p) method gives at 1172 and 1068 cm-1. The inplane bending in the ring of the C–O–C and O–C–C
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bands are observed at 1148,664 cmin FTIR and 698 cmin Raman; 1104, 668 cmand 1172,700cmin B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) respectively. The out of plane bending of O–C–C bands are observed at 645 cm-1 in B3LYP/6-311+G(d,p) and 687 in HF/6-311+G(d,p).
The most characteristics vibrations are those of C – H and C – C stretching and bending. The bonding of CH3 or CH2 to atoms other than carbon or carbonyl group or aromatic or hetroaromatic ring may cause appreciable shifts the C – H stretching and bending frequencies.
The methyl group is assigned to nine fundamental modes of vibration. Three stretching vibration, one being symmetric and other two asymmetric; three bending vibrations of scissoring, wagging and twisting; two rocking vibrations of inplane and out of plane and single torsion vibration describe the motion of the methyl group [19].
The CH3 symmetric and asymmetric stretching vibrations generally occur at the region 2850-3000cm-1 . This region is characterized for the confirmation of methyl stretching vibration. The CH3 asymmetric stretching
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frequencies are expected in the regions 2985 20 cmand 2955 20 cmin which two C-H bonds are extending while the third one is contracting.
In the present study, CH3 asymmetric stretching vibrations are observed at 3001 cm-1 weak intense in IR and very strong intense in Raman spectra at 3004 cm-1. The B3LYP/6-311+G(d,p) gives the frequencies values for CH3 asymmetric stretching at 3001and 2950 cm-1and the HF/6-311+G(d,p) method gives at 3001 and 2961cm-1.The CH3 symmetric stretching vibrations is expected in the region 2845 45 cm-1 in which all the three C-H extend and contract in phase.
Table 2. Vibrational assignments of ABL
The CH3 symmetric stretching vibration found in Raman spectrum intense bands at 2920cm-1 which
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also found in FT-IR at 2923 cm. The B3LYP/6-311+G(d,p)calculation frequencies at 2895cm, 2889 cm-1 and HF/6-311+G(d,p) calculation frequencies 2900, 2892 cm-1 .
The CH3 scissoring vibration are assigned at 1409 and1400 cm-1 in B3LYP/6-311+G(d,p); 1458, 1446 in HF/6-311+G(d,p) (Not observed experimentally). The CH3 wagging vibration observed in B3LYP/6
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311+G(d,p) at 1326 cmand HF/6-311+G(d,p) at 1394 cm(not observed experimentally). The CH3 rocking modes are expected in the region [40] 1100 95cm-1and 1180 80cm-1. The experimental frequencies of methyl
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rocking are observed in FT-IR at 1022, 1001, 785 cmand which also observed at 965, 784 cmin FT-Raman. The B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) calculations gives the CH3 rocking frequencies at 1023,
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998,828, 754cmand 1081, 1067,860, 796 cmrespectively. The CH3 torsion vibration is assigned in FT
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Raman at 70 cmand theoretically observed at 136 cmand 119 cmin B3LYP/6-311+G(d,p) and HF/6311+G(d,p) calculations respectively.
The CH2 group can assigned basically six fundamental modes of vibrations namely CH2 symmetric and asymmetric stretching vibration, CH2 bending vibrations of scissoring, rocking, wagging, and twisting modes [20].
The asymmetric CH2stretching vibration generally observed in the region 3000–2900cm-1, while the CH2 symmetric stretch will appear between 2900 and 2800cm-1[50]. In the present study, Very strong intense band appear in the FT-Raman for CH2 asymmetric stretching at 2968 and 2923 cm-1 and weak intense in FT-IR
at 2920 cm -1.The calculated bands observed at 2984, 2972 cm -1 in B3LYP/6-311+G(d,p) and 2998, 2982,
2900cm-1 in HF/6-311+G(d,p). The symmetric CH2 stretching vibration in FT-Raman very strong intense band
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appears at 2968 cm. The calculated bands observed at 2971, 2910, 2895 cmin B3LYP/6-311+G(d,p) and 2981, 2940, 2923 cm-1 in HF/6-311+G(d,p) method.
In the present assignment, the CH2 bending modes follow, in decreasing wavenumber, the general order CH2 scissoring CH2 wagging CH2 twist CH2 rock. Since the bending modes involving hydrogen atom attached to the central carbon falls into the1485–645 cm-1 range.
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The scissoring frequencies are observed at 1423 cmin IR spectrum and 1485, 1424 cmin Raman spectrum. The CH2 scissoring vibrations are assigned in B3LYP/6-311+G(d,p) at 1458, 1435 cm-1 and 1514,
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1483 cmin HF/6-311+G(d,p). The CH2 wagging frequencies are found at 1360 in FTIR and 1279 cmin FT-Raman. The theoretical observations in B3LYP/6-311+G(d,p) at 1290, 1075 cm -1 and HF/6-311+G(d,p) at
-1-1-1
1403, 1368, 1118 cm. The CH2 twisting vibrations are observed at 1217 cm(FTIR); 1210 cm(FT-Raman);
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1249, 1200, 1178 and 1154 cmin B3LYP/6-311+G(d,p); 1305, 1277, 1237, 1206 cmin HF/6-311+G(d,p). The CH2 rocking vibrations are assigned at 785 cm-1(FTIR); 784cm-1(FT-Raman); 1134, 952, 935, 828, 754,
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255cmin B3LYP/6-311+G(d,p); 1192,978,964,860,796,259 cmin HF/6-311+G(d,p).
Fig.3 :Comparison of FTIR of ABL Fig.4Comparison of FTR spectra of ABL
The hetero cyclic organic compounds and its derivatives are commonly exhibit intense peaks in the region 3250-3000 cm-1 due to C-H stretching vibration [21]. In the present study, the C-H stretching frequencies
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are observed in FT-IR at 2920 cmand 2923 cmin FT-Raman. B3LYP/6-311+G(d,p) and HF/6-311+G(d,p)
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methods gives at 2932, 2911, 2895, 2889cmand 2940, 2924, 2900, 2892 cmrespectively. The out of plane bending vibrations occur in the region700-1000cm-1, and inplane bending vibrations in the region 1000-1520 [22]. In our present study, the inplane bending experimental bands are observed at 1217 cm-1 in FT-IR and
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1279, 1210 cmin FT-Raman. The theoretical calculated vibrations has been observed at 1200 90 cmin both B3LYP/6-311+G(d,p) and HF/6-311+G(d,p). The out of plane bending vibrations has been observed at 998 77 cm -1 in both B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) methods. The experimental bands are observed at 1022 cm-1 in FT-IR.
The C-C stretching frequencies are generally predicted in the region 650-1650 cm-1 [22]. In our present
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study, C-C stretching vibrations are observed at 937 cm in FT-IR spectrum and 938 cm in FT-Raman spectrum. The theoretical C-C stretching vibrations are found at 900 and 939 cm-1 in B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) respectively. The bands occurring at 465 and 453 cm-1 in FT-IR and FT-Raman spectra have been assigned to C-C-C out plane bending vibrations. The frequencies 550, 519, 442, 336 cm-1 and 581, 529, 461, 340 cm -1 are assigned to C-C-C out of plane bending in B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) respectively .The inplane bending vibrations are found at 884 and 917 cm-1 in B3LYP/6-311+G(d,p) and HF/6311+G(d,p) respectively ( Not observed experimentally)[23]
The comparison of experimental and calculated FT-IR and FTRaman spectra of the title compound are given in the Fig 3.
The electronic absorption of the title compound was recorded within the 200-800 nm range and the experimental UV absorption spectrum is given in the Fig 5.
Fig 5 The experimental VU-Vis absorption spectrum of ABL
From this experimental UV spectrum, the maximum obserption values have been found to be 241, 310,
472 and 568 nm. these values may be slightly shifted by solvent effects. The broad absorption bands associated to a strong * and a weak * transition characterize the UV-Vis absorption spectra. The max is a function of substituent, the stronger the donor character substitution, the more electrons transition into the
molecules, the larger
max [24].
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are the most important parameters in quantum chemistry molecule [25-26]. HOMO, which can be thought as the outer orbital containing electrons, tends to give these electrons as an electron donor and hence the ionization potential (IP) is directly related to the energy of the HOMO. On the other hand LUMO can accept electrons and the LUMO energy is directly related to electron affinity (EA).Energy difference between HOMO and LUMO orbitals is called as energy gap ( E) that is an important stability for structures. From the HOMO–LUMO energy gap, one can find whether the molecule is hard or soft. The molecules having large energy gap are known as hard and molecules having a small energy gap are known as soft molecules. A molecule having a small energy gap is more polarizable and is generally associated with a high chemical reactivity and low kinetic stability [27].
In the present study, the HOMO and LUMO energies are calculated by DFT/B3LYP/6-311+G(d,p) method. Accordingly to the results, the ABL molecule contains 34 occupied molecular orbitals and 212 unoccupied molecular orbitals.The few important molecular orbitals (MOs) were examined for the title compound, the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) which are given inFig 6. The HOMO and LUMO energies have been focused in order to determine it correlations with interesting molecular/atomic properties and chemical quantities exist and which are, calculated by following expressions [28] and listed in Table 3.;
Ionization potential (IP) = - Electron affinity (EA) = - Global softness (S) = 1/2
Global hardness ( ) = Electronegativity ( ) =
Chemical potential or Fermi energy ( ) = -= Electrophilicity ( ) =
Table 3. HOMO-LUMO energy values of ABL at DFT/ B3LYP/6-311+G(d,p) Fig 6 HOMO-LUMO analysisof ABL
Mulliken charges arise from the Mulliken population analysis [29] and provide a means of atomic charge distribution in the molecule from carried out computational methods. In the application of Quantum mechanical calculations to molecular system, the atomic charges calculations play in important role [30]. Mulliken atomic charge calculation values have been shown in the Table 4.4 using DFT/B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) methods.
Normally, the Carbon atom having negative charge but in our title molecule, carbon atoms shows negative charge only that it is attached with Hydrogen atoms, whereas the remaining carbon atoms are positive
[31] like C7 and C8 carbons atoms are bonded to oxygen atoms, which are shows positive charge due the electrons withdrawing nature of the oxygen atoms [32]. The atom O2 and O3 are shows greater negativity than the atom O1, due to these O2 and O3 atomsare double bond attachment with Carbon atom. In our title molecule, all the Hydrogen atoms are having positive charge. These charge distribution on the molecule has animportant influence on the vibrational spectra. The Mullikencharge distribution analysis graph is shown in the Fig 7 and listed in Table 4 using DFT/B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) methods.
On the basis of vibrational analysis at DFT/B3LYP/6-311+G(d,p) and HF/6-311+G(d,p) level, several thermodynamic parameters are calculated and are presented in the Table 5. All the thermodynamic properties are helpful information for further study of the title molecule.
This can be used to compute the other thermodynamic energies according to relationship of thermodynamic functions and estimate direction of chemical reactions according to second law ofthermo dynamical field. The value of zero point vibrational energy (ZPVEs) in B3LYP/6-311G(d,p) is lower than HF/6-311G(d,p) method but the value of specific heat capacity (C) and entropy (S) are in B3LYP/6-311G(d,p) higher than HF/6-311G(d,p) method. Dipole moment reflects the molecular charge distribution and is given as vector in three dimensions [62]. Therefore it can be used as descriptor to depict the charge movement across the molecule depends on the centre of positive and negative charges. The total dipole moment of ABL is calculated by B3LYP/6-311G(d,p) and HF/6-311G(d,p) methods are 3.9888 and 4.5060 Debye, respectively.
In the present investigation thoroughly analyzed geometrical parameters, the vibrational spectra of both IR and Raman, HOMO-LUMO analysis of – acetyl -– butyrolactone using DFT/B3LYP and HF methods with 6-311+G(d,p) basis sets. Atomic charge distribution and thermodynamic properties were also determined by using DFT/B3LYP and HF methods. The theoretical results were compared with experimental results. The small differences between experimental and theoretical values are observed due to fact that the experimental result belongs to solid phase and a theoretical calculation belongs to gaseous phase. It is clear that, most reliable theoretical information isprovidedby DFT/B3LYP/6-311+G(d,p) based quantum mechanical approachesfor the molecule.The calculated HOMO and LUMO energy gap, chemical hardness and softness of the molecule are indication of the chemical stability of the molecule. The electronic transitions in UV-Vis spectra were analyzed for understanding the properties and activities of the molecule. In conclusion, all the calculated data and simulations not only show the way to the characterization of the molecule but also help for the application in fundamental researches in Chemistry, Pharmaceutical and biological industries in the future.
11. Rajalakshmi.K, Gunasekaran.S, Kumaresan.S, (2014) "Vibrational assignment, HOMO-LUMO and NBO analysis of (2S)-2-[(2{[(2S)-1-hydrxybutan-2-yl] amino}ethyl)amino]butan-1-ol by density functional theory ”, SpectrochimicaActa Part A: Molecular and Biomolecular spectroscope, Vol 130, pp 466-479.
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