This study is based on the analysis of the results reproduced by BYLP, BPV86, B3LYP, B3PW91 and PBEPBE functionals with STO-3G, DGDZVP, 6–311G, 6–311 + G(2d) and 6–311 + G(d, p) basis sets at the DFT level. To test the performance of different functionals and basis sets and to verify discovery of the molecular properties, we have carried out benchmark calculations on the energetic, reactivity and spectroscopic properties of the 2C68DMQCALD molecule.
3.1. Structural and Energetic Analyses
The optimized geometry (at the B3LYP/6-311G level of theory) of the 2C68DMQCALD molecule is presented in Fig. 1. The molecule has a very large dipole moment in the range of 4.084 to 5.437 Debye (Table 1); thus, it indicates a polar structure. Besides, it contains twelve C – C, ten C – H, two C – N and one C – Cl, C – O bond lengths. The changes in basis sets and functionals depending on bond lengths (C – N and C – Cl) between two different atoms are presented in Table 1. The calculated bond lengths for C11 – N13 range from 1.292 Å – 1.346 Å and C11 – Cl14range from 1.755 Å – 1.887 Å by different functionals and basis sets. Compared to other functionals, the B3PW91 functional generally computes the lower bond lengths (for C – N and C – Cl), whereas the BLYP predicts higher bond lengths.
Table 1
Structural and electronic properties and spectroscopic constants of 2-choloro-6,8-dimethylquinoline-3-carboxaldehyde molecule at different functionals and basis sets.
Functional
|
Basis Set
|
Etot
|
Eb
|
DM
|
Bond length (A0)
|
Frequency (cm− 1)
|
HOMO
|
LUMO
|
Eg
|
|
|
(a.u.)
|
(eV)
|
(Debye)
|
C11-N13
|
C11-Cl14
|
υ1 unscaled
|
υ1 scaled
|
(eV)
|
B3LYP
|
STO–3G
|
-1041.039
|
6.94
|
4.084
|
1.346
|
1.827
|
48.4
|
0.892
|
43.1
|
– 4.493
|
– 0.081
|
4.41
|
B3LYP
|
DGDZVP
|
-1053.508
|
5.96
|
4.421
|
1.299
|
1.772
|
53.1
|
0.965
|
51.3
|
– 6.782
|
– 2.711
|
4.07
|
B3LYP
|
6–311G
|
-1053.466
|
5.81
|
5.155
|
1.296
|
1.850
|
54.6
|
0.966
|
52.7
|
– 6.925
|
– 2.818
|
4.10
|
B3LYP
|
6–311 + G(2d)
|
-1053.670
|
5.98
|
4.367
|
1.292
|
1.770
|
52.9
|
0.965
|
51.0
|
– 6.803
|
– 2.722
|
4.08
|
B3LYP
|
6–311 + G(d,p)
|
-1053.668
|
5.97
|
4.425
|
1.294
|
1.772
|
52.2
|
0.965
|
50.3
|
– 6.814
|
– 2.749
|
4.06
|
BVP86
|
STO–3G
|
-1041.150
|
7.27
|
4.153
|
1.360
|
1.834
|
49.0
|
0.900
|
44.1
|
– 2.982
|
– 0.915
|
2.06
|
BVP86
|
DGDZVP
|
-1053.578
|
6.23
|
4.577
|
1.309
|
1.777
|
49.4
|
0.960
|
47.4
|
– 6.127
|
– 3.485
|
2.64
|
BVP86
|
6–311G
|
-1053.554
|
6.02
|
5.301
|
1.306
|
1.858
|
50.7
|
0.964
|
48.9
|
– 6.145
|
– 3.597
|
2.54
|
BVP86
|
6–311 + G(2d)
|
-1053.738
|
6.20
|
4.505
|
1.302
|
1.773
|
49.3
|
0.960
|
47.3
|
– 6.153
|
– 3.495
|
2.65
|
BVP86
|
6–311 + G(d,p)
|
-1053.736
|
6.24
|
4.563
|
1.304
|
1.776
|
48.3
|
0.960
|
46.4
|
– 6.185
|
– 3.522
|
2.66
|
B3PW91
|
STO–3G
|
-1040.862
|
7.09
|
4.116
|
1.343
|
1.816
|
53.3
|
0.885
|
47.1
|
– 4.518
|
– 0.133
|
4.38
|
B3PW91
|
DGDZVP
|
-1053.215
|
6.12
|
4.349
|
1.298
|
1.757
|
52.7
|
0.961
|
50.7
|
– 6.847
|
– 2.744
|
4.10
|
B3PW91
|
6–311G
|
-1053.176
|
5.97
|
5.057
|
1.296
|
1.829
|
54.2
|
0.963
|
52.2
|
– 6.969
|
– 2.846
|
4.10
|
B3PW91
|
6–311 + G(2d)
|
-1053.381
|
6.14
|
4.281
|
1.291
|
1.755
|
52.7
|
0.961
|
50.6
|
– 6.830
|
– 2.725
|
4.10
|
B3PW91
|
6–311 + G(d,p)
|
-1053.377
|
6.13
|
4.339
|
1.293
|
1.757
|
52.0
|
0.961
|
49.9
|
– 6.843
|
– 2.754
|
4.08
|
PBEPBE
|
STO–3G
|
-1040.166
|
7.35
|
4.135
|
1.358
|
1.829
|
49.6
|
0.914
|
45.3
|
– 2.852
|
– 0.820
|
2.03
|
PBEPBE
|
DGDZVP
|
-1052.582
|
6.22
|
4.522
|
1.309
|
1.772
|
49.1
|
0.961
|
47.2
|
– 6.000
|
– 3.387
|
2.61
|
PBEPBE
|
6–311G
|
-1052.550
|
6.16
|
5.233
|
1.306
|
1.851
|
50.3
|
0.963
|
48.4
|
– 6.001
|
– 3.488
|
2.52
|
PBEPBE
|
6–311 + G(2d)
|
-1052.736
|
6.24
|
4.457
|
1.302
|
1.768
|
48.9
|
0.961
|
47.0
|
– 6.040
|
– 3.411
|
2.62
|
PBEPBE
|
6–311 + G(d,p)
|
-1052.734
|
6.30
|
4.521
|
1.304
|
1.770
|
47.9
|
0.961
|
46.0
|
– 6.069
|
– 3.437
|
2.63
|
BLYP
|
STO–3G
|
-1040.709
|
6.97
|
4.098
|
1.365
|
1.849
|
48.4
|
0.925
|
44.8
|
– 2.790
|
– 0.690
|
2.10
|
BLYP
|
DGDZVP
|
-1053.276
|
5.95
|
4.684
|
1.311
|
1.799
|
49.6
|
0.965
|
47.8
|
– 3.220
|
– 5.870
|
2.65
|
BLYP
|
6–311G
|
-1053.249
|
5.76
|
5.437
|
1.305
|
1.887
|
50.6
|
0.998
|
50.5
|
– 5.905
|
– 3.348
|
2.55
|
BLYP
|
6–311 + G(2d)
|
-1053.432
|
5.86
|
4.622
|
1.302
|
1.795
|
49.0
|
0.995
|
48.8
|
– 5.938
|
– 3.272
|
2.66
|
BLYP
|
6–311 + G(d,p)
|
-1053.431
|
5.91
|
4.684
|
1.304
|
1.798
|
48.2
|
0.995
|
47.9
|
– 5.947
|
– 3.299
|
2.64
|
The total energies \({(E}_{tot})\) are listed in Table 1. The calculated \({E}_{tot}\) values range from 1041 to 1053 a.u. by different functionals and basis sets. As seen in Fig. 2, going from the PBEPBE functional to BVP86, the \({E}_{tot}\) increases on average by 1.002 a.u., with the maximum changes of 0.983 a.u. for STO-3G, 1.004 a.u. for 6-311G, 0.996 a.u. for DGDZVP, 1.002 a.u. for 6-311 + G(d, p) and 1.002 a.u. for 6-311 + G(2d). These results show that all \({E}_{tot}\) values obtained from BVP86 functional are lower than that of the other functionals. When compared all results, the 6–311 + G(2d) basis set calculates the lowest energy value (with − 1053.73842 a.u.), but the STO-3G basis set calculates the higher \({E}_{tot}\) values than the others.
The binding energies per atom \(\left({E}_{b}\right)\) of the 2C68DMQCALD molecule depending on the functionals and basis sets are listed in Table 1. The \({E}_{b}\) is an important parameter for evaluating the structural stability of the molecule. As seen in Fig. 3, going from the 6-311G basis set to STO-3G, the \({E}_{b}\) changes on average by 1.178 eV, with the maximum changes of 1.211 eV for BLYP, 1.122 eV for B3LYP, 1.123 eV for B3PW91, 1.244 eV for BVP86 and 1.188 eV for PBEPBE. By using the BLYP, B3LYP, B3PW91, BVP86 and PBEPBE functionals with the 6-311G basis set, the \({E}_{b}\) values are found as 5.76, 5.81, 5.97, 6.02 and 6.16 eV, respectively. Among the studied basis sets, the STO-3G and 6-311G basis sets predict the highest \({E}_{b}\) (with 7.35 eV) and the lowest \({E}_{b}\) (with 5.76 eV) values, respectively. Considering all obtained results, the PBEPBE functional calculates generally the highest energy (with − 1053.73842 a.u.), but the BYLP calculates generally the lower \({E}_{b}\) values than the others. Besides, the contribution of diffuse and polarized functions is critical to fully describe hydrogen bonded systems [39]. In this sense, the contribution of the diffuse and polarized functions to the 6-311G basis set clearly increases the \({E}_{tot}\) and \({E}_{b}\) values. Furthermore, the thermodynamic parameters are commonly examined in the study of reaction mechanisms of an organic molecule. Table S1 (see Supporting Information) shows the calculated zero-point vibrational energies, rotational constants, and entropies (translational, rotational, vibrational, and total) by different functionals (and basis sets).
3.2. Frontier Molecular Orbitals Analysis
To provide the extra knowledge on the performance of different functionals and basis sets, the HOMO-LUMO energy gaps \(\left({E}_{g}\right)\) were analyzed and listed in Table 1. The B3LYP and B3PW91 functionals resulted in the largest \({E}_{g}\) in the range of 4.06–4.41 eV, whereas all the other functionals have narrower \({E}_{g}\) values (in the range of 2.03–2.66 eV). As seen also in Fig. 3, the \({E}_{g}\) generally increases going from the PBEPBE functional to P3PW91. On the other hand, the STO-3G basis set calculates the lowest \({E}_{g}\) values for PBEPBE, BVP86 and BLYP functionals, but gives higher values for B3LYP and B3PW91 (see Fig. 4). It can be concluded that the STO-3G basis set resulted in the widest \({E}_{g}\) values due to the shift of HOMO electrons to deeper energy levels. It is worth noting that the analysis of the precision of the calculated \({E}_{g}\) cannot be performed without precise experimental data.
To better understand these changes in the electronic levels, we computed the density of states (DOS) of the 2C68DMQCALD molecule. Figure 5 shows the DOS using B3LYP/6-311G, B3PW91/STO-3G, BLYP/DGDZVP and BPV86/6-311G+(2d) levels of theory. Compared to HOMO and LUMO energies, BVP86, PBEPBE and BLYP calculate low and compatible values, at the same time, B3LYP and B3PW91 calculate compatible values, but higher than the other functionals (see Table 1). In terms of basis sets, it is worth noting that the \({E}_{g}\), HOMO and LUMO energies do not change much depending on the addition of polarization and diffuse functions. In general terms, the frontier molecular orbitals of the 2C68DMQCALD molecule depend critically on the chosen functional but are less varied through different basis functions.
Figure 6 shows the frontier molecular orbital (HOMO and LUMO) patterns of the 2C68DMQCALD molecule at B3LYP/6-311G level of theory. The frontier molecular orbital theory provides potentially useful information about the intramolecular charge transfer, i.e., the electrons transfer from HOMO to LUMO that attempted to explain the reactivity properties of the 2C68DMQCALD molecule. Besides, Koopmans theorem is often associated with frontier molecular orbital theory [40], i.e., the ionization potential and electron affinity may be also calculated by the reverse sign of HOMO and LUMO values, respectively. In this study, the ionization potentials (IP) and electron affinities (EA) of the 2C68DMQCALD molecule were found to be in the range of 3 eV < IP < 7 eV and 0.5 eV < EA < 3.5 eV (Table 2). The reason why IP and EA values are calculated over a wide range is that the STO-3G basis set does not calculate the HOMO and LUMO values accurately. For this reason, it calculates the lowest IP and EA values. On the other hand, the important reactivity parameters such as the hardness (\(\eta\)), the chemical potential (\(\mu\)), the electrophilicity index (\(\omega\)) and maximum amount of electronic charge index \(\left(\varDelta {N}_{tot}\right)\) can be calculated in terms of HOMO and LUMO energies based on the Koopmans theorem using the equations: \(\eta (IP-EA)/2\), \(\mu -(IP+EA)/2\), \(\omega {\mu }^{2}/2\eta\)and\(\varDelta {N}_{tot}=-\mu /\eta\)[41]. Herein, the \(\eta\) indicate the molecular stability and the ω can be used to predict the ability of a molecule to bind to biomolecules [42]. The global reactivity values of the 2C68DMQCALD molecule are in the range of 1.0 eV < \(\eta\) < 2.2 eV for hardness, – 1.74 eV < \(\mu\) < – 4.9 eV for chemical potential, 1.2 eV < \(\omega\) < 9.4 eV for electrophilicity index and 1.0 eV < \(\varDelta {N}_{tot}\) < 3.8 eV for maximum amount of electronic charge index (Table 2). According to reactivity calculations, the 2C68DMQCALD molecule is stable and a strong electrophile and can react with much weaker nucleophiles due to the low chemical reactivity and high kinetic stability. When the reactivity parameters (\(\eta\), \(\mu\), \(\omega\) and \(\varDelta {N}_{tot}\)) found with respect to the functionals are compared, BVP86, PBEPBE and BLYP calculate high values that are consistent with each other. At the same time, B3LYP and B3PW91 calculate values that are consistent with each other, but lower than other functionals. Besides, it can be seen from Table 2that the addition of polarization and diffuse functions (DGDZVP, 6–311+G(d, p) and 6–311+G(2d) to basis sets does not significantly affect the values of the calculated parameters.
Table 2
Comparison of reactivity parameters of 2-choloro-6,8-dimethylquinoline-3-carboxaldehyde molecule.
Functional
|
Basis Set
|
IP
|
EA
|
η
|
μ
|
ω
|
ΔNtot
|
|
|
(eV)
|
(eV)
|
(eV)
|
(eV)
|
(eV)
|
(eV)
|
B3LYP
|
STO–3G
|
4.493
|
0.081
|
2.206
|
– 2.287
|
1.185
|
1.037
|
B3LYP
|
DGDZVP
|
6.872
|
2.711
|
2.081
|
– 4.792
|
5.517
|
2.303
|
B3LYP
|
6–311G
|
6.925
|
2.818
|
2.054
|
– 4.872
|
5.778
|
2.372
|
B3LYP
|
6–311 + G(2d)
|
6.803
|
2.722
|
2.041
|
– 4.763
|
5.558
|
2.334
|
B3LYP
|
6–311 + G(d,p)
|
6.814
|
2.749
|
2.033
|
– 4.782
|
5.624
|
2.352
|
BVP86
|
STO–3G
|
2.982
|
0.915
|
1.034
|
– 1.949
|
1.837
|
1.885
|
BVP86
|
DGDZVP
|
6.127
|
3.485
|
1.321
|
– 4.806
|
8.742
|
3.638
|
BVP86
|
6–311G
|
6.145
|
3.597
|
1.274
|
– 4.871
|
9.312
|
3.823
|
BVP86
|
6–311 + G(2d)
|
6.153
|
3.495
|
1.329
|
– 4.824
|
8.755
|
3.629
|
BVP86
|
6–311 + G(d,p)
|
6.185
|
3.522
|
1.332
|
– 4.854
|
8.844
|
3.644
|
B3PW91
|
STO–3G
|
4.518
|
0.133
|
2.193
|
– 2.326
|
1.234
|
1.061
|
B3PW91
|
DGDZVP
|
6.847
|
2.744
|
2.052
|
– 4.796
|
5.605
|
2.337
|
B3PW91
|
6–311G
|
6.969
|
2.846
|
2.062
|
– 4.908
|
5.841
|
2.38
|
B3PW91
|
6–311 + G(2d)
|
6.830
|
2.725
|
2.053
|
– 4.778
|
5.56
|
2.327
|
B3PW91
|
6–311 + G(d,p)
|
6.843
|
2.754
|
2.045
|
– 4.799
|
5.631
|
2.347
|
PBEPBE
|
STO–3G
|
2.852
|
0.820
|
1.016
|
– 1.836
|
1.708
|
1.807
|
PBEPBE
|
DGDZVP
|
6.000
|
3.387
|
1.307
|
– 4.694
|
8.429
|
3.591
|
PBEPBE
|
6–311G
|
6.001
|
3.488
|
1.257
|
– 4.745
|
8.956
|
3.775
|
PBEPBE
|
6–311 + G(2d)
|
6.040
|
3.411
|
1.315
|
– 4.726
|
8.492
|
3.594
|
PBEPBE
|
6–311 + G(d,p)
|
6.069
|
3.437
|
1.316
|
– 4.753
|
8.583
|
3.612
|
BLYP
|
STO–3G
|
2.790
|
0.690
|
1.050
|
– 1.740
|
1.442
|
1.657
|
BLYP
|
DGDZVP
|
5.870
|
3.220
|
1.325
|
– 4.545
|
7.795
|
3.430
|
BLYP
|
6–311G
|
5.905
|
3.348
|
1.279
|
– 4.627
|
8.76
|
3.618
|
BLYP
|
6–311 + G(2d)
|
5.938
|
3.272
|
1.333
|
– 4.605
|
7.954
|
3.455
|
BLYP
|
6–311 + G(d,p)
|
5.947
|
3.299
|
1.324
|
– 4.623
|
8.071
|
3.492
|
3.3. MEP and Mulliken Atomic Charges Analyses
Molecular electrostatic potential (MEP) is based on electron density which associated with the dipole moment, electrical negativity, and the chemical reactivity of the 2C68DMQCALD molecule [43]. Therefore, it is suitable for predicting the interaction of molecules with each other. Figure 7 shows the optimized molecular structure calculated for MEP of the 2C68DMQCALD molecule using B3LYP/6-311 + G(2d). Accordingly, the CH and CH3 bonds have low intensity and positively charged (blue color) this means that the protons are repulsed by the atomic nucleus in this region, indicating a possible sites for nucleophilic attacks [44]. Besides, the C–N, C–O and C–Cl bonds have high intensity and negatively charged (red color), which means the attraction of the proton by the total electron density in the molecule. Therefore, the N, O and Cl atoms are more favorable sites for the electrophilic attack.
The Mulliken charge distributions of the 2C68DMQCALD molecule calculated at B3LYP/6-311 + G(2d) level of theory is plotted in Fig. 8. All the H atoms have positive charges ranging from 0.16 to 0.21 |e|. C atoms inside and outside the ring carry both negative and positive charges. However, C atoms outside the ring (C15, C18 and C22; see Fig. 1) carry more charges than those inside the ring. The C15 atom carries a positive charge after its bond with both the O and H atoms. Besides, the existence of enormous negative charge on N13 and O17 atoms are due to their electron withdrawing nature.
3.4. Vibration Analyses
The optimized structural parameters were used in the calculations of all fundamental vibrational frequencies to classify all the stationary points correspond to true minima on the potential energy surface. The 2C68DMQ3CA molecule contains twenty-five atoms, as it is nonlinear and has sixty-nine vibrational modes by 3N – 6. It has twelve carbon, ten hydrogen and one chlorine, nitrogen, and oxygen atoms. This molecule has sixty-nine vibrations. Among these vibrations, the intense bands observed in the experimental infrared spectrum, five method and five basis sets in each functional, were presented in Tables S1-S5 (see Supporting information) including some vibrational frequencies of the experimentally intense bands between vibration number twenty-eight and vibration sixty-nine. Theoretical vibrational frequencies were multiplied by the scale factors in all these basis sets. In addition, the experimental and theoretical infrared spectra of the 2C68DMQ3CA molecule are given in Fig. 9. When compared to experimental data, B3LYP/6-311G+(2d) combinations gives the best results in terms of vibration frequency values considering other combinations.
C – H stretching vibrations of the aromatic structure of the molecule are characterized in the region of 3200–3000 cm− 1 in the infrared spectra [45–47]. The experimental spectra show that all the C – H stretching vibrations give rise to bands in the region 3046–3016 cm− 1 in the aromatic structures [48], and so C – H stretching vibrations are almost at same frequencies. The theoretically calculated aromatic C – H stretch vibration frequencies in this region are compatible with the experimental results. Furthermore, the ring C – H stretching vibrations appear to be weak due to steric interactions [49].
For the C–N stretching vibrations of the 2C68DMQ3CA molecule, some vibration frequencies, which we selected as very intense in the experimental spectrum, were observed as 1338, 1224 and 1199 cm− 1. Theoretical frequencies for these vibrations are 1381 − 1118 cm− 1, 1364 − 1158 cm− 1, 1348 − 1128 cm− 1, 1363 − 1197 cm− 1, 1374 − 1162 for the B3LYP, BVP86, B3PW91, PBEPBE, BLYP methods, respectively.
The C–H stretch vibration frequencies of the methyl group in the 2C68DMQ3CA molecule are marked around 3000 cm− 1 [50, 51]. These bands were measured in the range of 2983–2880 cm− 1 in the experimental spectrum. All theoretical calculations for the frequencies of these vibrations of the methyl group are consistent with the experimental results.
The stretching vibration of the O–C bond was observed at 1691 cm− 1 in the experimental spectrum. Another vibration in the 2C68DMQCALD molecule is the stretching vibration between the C–Cl atoms. The frequency of this vibration was observed at 782 cm− 1 in the experimental which is compatible with theoretical data.
There are slight differences in the experimental and theoretical frequency values of all these vibrations we discussed. One of the reasons for this; The fact that the 2C68DMQ3CA molecule is in the solid phase in experimental measurements and in the gas phase in theoretical calculations can be evaluated as [52]. Another reason for these differences is the weak intermolecular hydrogen bond [53].
The theoretical and experimental predicted infrared spectra in 4000–500 cm− 1 regions, as seen in Fig. 9. The B3LYP vibrational frequencies are significantly closer to the experimental frequencies than the scaled other functionals’ frequencies. In addition, inside the B3LYP functionals, 6-311 + G(2d) basis set is the most compatible with experimental data. Taking into account computational cost of several basis sets, we propose the combination of B3LYP with the 6-311 + G(2d) basis set, i.e., B3LYP/6-311 + G(2d), as an accurate and a practical method to analyses FT- IR spectra. A remarkably good agreement and strong similarity between the theoretical (at B3LYP/6-311 + G(2d) level of theory) and experimental frequencies and intensities of the infrared spectra can be also seen from Table 3. On the other hand, Tables S2 – S5 (see Supporting Information) depict the comparison of some vibration frequencies of the 2C68DMQCALD molecule by BLYP, BPV86, BPW91 and PBEPBE functionals and STO-3G, 6-311G, 6-311G+, 6-311G+(2d) and DGDZVP basis sets.
Table 3
Comparison of some vibration frequencies of 2-choloro-6,8-dimethylquinoline-3-carboxaldehyde molecule experimentally and theoretically (with B3LYP functional) in FT-IR spectra.
Experimental
|
Theoretical (FT-IR with B3LYP functional)
|
Normal
Modes
|
FT-IR*
|
in STO-3G
|
in 6-311G
|
in 6-311G +
|
in 6-311G + 2D
|
in DGDZVP
|
Frequencies
|
Frequencies
|
Frequencies
|
Frequencies
|
Frequencies
|
Calc.
|
Scaled a
|
Calc.
|
Scaled b
|
Calc.
|
Scaled c
|
Calc.
|
Scaled d
|
Calc.
|
Scaled e
|
ν67
|
3046 w
|
3458
|
3085
|
3160
|
3053
|
3152
|
3045
|
3133
|
3023
|
3171
|
3060
|
ν66
|
3016 w
|
3457
|
3084
|
3108
|
3002
|
3113
|
3007
|
3104
|
2995
|
3143
|
3033
|
ν64
|
2983 w
|
3442
|
3070
|
3088
|
2983
|
3091
|
2986
|
3083
|
2975
|
3126
|
3017
|
ν62
|
2957 w
|
3307
|
2950
|
3044
|
2941
|
3038
|
2935
|
3037
|
2931
|
3050
|
2943
|
ν61
|
2921 w
|
3304
|
2947
|
3031
|
2928
|
3024
|
2921
|
3023
|
2917
|
3037
|
2931
|
ν60
|
2880 w
|
3233
|
2884
|
3016
|
2913
|
2987
|
2885
|
2973
|
2869
|
3022
|
2916
|
ν57
|
1572 vs
|
1695
|
1512
|
1607
|
1552
|
1617
|
1562
|
1614
|
1558
|
1627
|
1570
|
ν51
|
1486 s
|
1566
|
1397
|
1508
|
1457
|
1475
|
1425
|
1493
|
1441
|
1493
|
1441
|
ν50
|
1450 vs
|
1564
|
1395
|
1463
|
1413
|
1456
|
1406
|
1458
|
1406
|
1464
|
1413
|
ν49
|
1419 m
|
1543
|
1376
|
1460
|
1410
|
1432
|
1383
|
1436
|
1386
|
1442
|
1392
|
ν44
|
1338 s
|
1394
|
1243
|
1385
|
1338
|
1374
|
1327
|
1374
|
1326
|
1381
|
1333
|
ν42
|
1224 s
|
1327
|
1184
|
1305
|
1261
|
1284
|
1240
|
1288
|
1243
|
1291
|
1246
|
ν41
|
1199 vs
|
1252
|
1118
|
1237
|
1195
|
1229
|
1187
|
1226
|
1183
|
1235
|
1192
|
ν33
|
1001 vs
|
1043
|
930
|
1040
|
1005
|
1028
|
993
|
1033
|
997
|
1025
|
989
|
ν30
|
941 s
|
971
|
866
|
980
|
947
|
965
|
932
|
968
|
934
|
964
|
930
|
ν28
|
860 s
|
913
|
814
|
895
|
865
|
871
|
841
|
872
|
841
|
868
|
838
|
*vs: very strong, m: medium, s: strong, w: weak. |
a Scaling factor: 0.892; b,c Scaling factor: 0.966; d,e Scaling factor: 0.965. |
Figure 10 shows the deviations of the calculated FT-IR spectra from the experiment FT-IR spectra of the 2C68DMQCALD molecule using B3LYP functional with different basis sets. The deviations from the experiment are, overall, not drastic, about 0.90–6.62% for 6-311G, -0.74–4.90% for 6-311G+, 0.47–5.23% for 6-311G+(2d), 0.47–5.47% for DGDZVP basis sets. However, the increase in deviation from the experiment is with the largest change being observed for STO-3G basis set (in range of 3.19–15.39%). Comparing increases in deviation from experiment by modes, the increase in deviation from the experiment was observed for the lowest variation at DGDZVP basis set (with ν28, ν30 and ν33 modes), at 6-311G + basis set (with ν42, ν49 and ν50 modes) and at 6-311G+(2d) basis set (with ν41, ν44, ν51, ν57, ν60, ν61, ν62, ν64, ν66 and ν67 modes). Generally, speaking, the 6-311G, 6-311G+, 6-311G+(2d) and DGDZVP basis sets compute FT-IR spectra closer to experiment and better than STO-3G basis.