chapter 6 spectroscopic characterization...

CHAPTER 6

SPECTROSCOPIC CHARACTERIZATION AND QUANTUM

CHEMICAL COMPUTATIONAL STUDIES ON

4-METHYL-N-(3-METHYLPHENYL)BENZENE SULFONAMIDE

6.1 INTRODUCTION

Aromatic amines are very important in biology and chemical industry.

Particularly, aniline and its derivatives are used in the production of dyes,

pesticides and antioxidants.

Meta-toluidines (3-methylaniline) are viscous liquids at room temperature

and pressure. They have been widely used as starting materials in a vast amount of

pharmaceutical, electro-optical and many other industrial processes. Hence,

understanding of their molecular properties as well as the natures of reaction

mechanisms they undergo has great importance. That is why investigations on the

structures and the vibrations of aniline and substituted anilines are still being

carried out, increasingly [1–7].

Altun et al [8–9] studied theoretical and experimental studies of the

vibrational spectra of m-methylaniline. In their study, comparative ab initio and

DFT calculation results of m-methylaniline had been carried out. Complete

vibrational mode and frequency analyses of m-methylaniline had been analysed.

They also analysed thermal properties of complexes of the m-methylaniline from

the DSC curves.

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154

2-(methylthio)aniline had been studied by applying the DFT calculations

based on Becke3-Lee-Yang-Parr (B3LYP) level with 6-31G* basis sets by Krishna

Kumar et al [10].

Shaji et al [11] studied the conformational structural analysis and NIR

vibrational overtone spectra of N-methylaniline, N, N-dimethylaniline and

N, N-diethylaniline using local mode model. The analysis of the mechanical

frequency values of C-H and N-H oscillators reveal the molecular conformation of

these molecules. This illustrates the use of overtone spectroscopy as an effective

tool for the study of molecular structure, conformational aspects and substituent

effects.

Santo et al [12] reported molecular structures and vibrations of

m-methylaniline in the S0 and S1 states studied by laser induced fluorescence

spectroscopy and ab initio calculations. Ab initio calculations had been carried out

to obtain the structural parameters of m-methylaniline in both the ground and

excited singlet states, at MP2:6-31G* and CIS:6-31G* levels of theory.

Jayalakshmi et al and Gowda et al [13-15] reported Infrared and 1H and 13C NMR spectra of N-(substituted phenyl)methanesulphonamides includes N-(2-

ethylphenyl)methanesulfonamide and N-(3-methylphenyl)methanesulfonamide.

They also analyzed the X-ray crystallographic structure of these two compounds

Dodoff [16] studied the Infrared spectra and the conformational features of N-3-

pyridinylmethanesulfonamide) using molecular mechanics and HF ab initio

calculations. Recently, Karabacak et al [17] studied a spectroscopic study of some

para-halogen benzenesulfonamides, 4-X-C6H4SO2NH2 (X = F, Cl or Br) by

ab initio and density functional theory calculations.


155

Though lot of reports are available in the literature on structural, spectral

and DFT studies of meta-aniline, similar studies on sulfonated meta-aniline is

scarce. The vast majority of sulfonamides are prepared from the reaction of a

sulfonyl chloride with ammonia or primary or secondary amines or via related

transformations. [18,19].

The purpose of this work is to investigate experimentally and theoretically

structural and spectroscopic properties of 4M3MPBS. The sulfonamide compound

4-methyl-N-(3-methylphenyl) benzenesulfonamide was synthesised and

characterized by X-ray single crystal diffraction technique, IR, Raman-NMR, UV

spectroscopy and quantum chemical computational methods as both

experimentally and theoretically. The molecular geometry was also optimized

using density functional theory (DFT/B3LYP) methods with the 6-31G(d,p) basis

set [20-23] and compared with the experimental data. The results of the optimized

molecular structure are exhibited and compared with the experimental X-ray

diffraction and the calculated results are show that the optimized geometry can

well reproduce the crystal structure. From the optimized geometry of the molecule,

vibrational frequencies, gauge-independent atomic orbital (GIAO) 1H and 13C

NMR chemical shift values, molecular electrostatic potential (MEP) distribution,

non-linear optical properties, frontier molecular orbitals (FMO) of 4M3MPBS

compound have been calculated in the ground state theoretically. The theoretical

result showed good agreement with the experimental values.

6.2 SYNTHESIS

Meta toluedene (5.4 gm), Triethylamine (4 ml) were dissolved in acetone

(4 ml). To this solution, Para toluene sulfonyl chloride (9.53 gm) in acetone

(12.5 ml) was added in drops with continuous stirring for two hours. The resulting


CH3

SO2Cl

+

NH

CH3

SO2NH

ACETONE

︵C 2H5 ︶3N2

CH3

CH3

Figure 6.1 Pathway synthesis of 4M3MPBS


156

solution was allowed to evaporate. The residue was washed several times with

water and then with petroleum ether solution (The pathway synthesis of the

4M3MPBS reported earlier [24] is different and that reactions subjected to heating

and cooling). The crude product of the title compound was recrystallized from

ethanol. After one week pale yellow crystals suitable for X-ray diffraction studies

were obtained. The scheme of the synthesis is shown in Figure 6.1.

6.3 SINGLE CRYSTAL X-RAY DIFFRACTION ANALYSIS

6.3.1 Crystal Structure Determination

A crystal with dimensions of 0.28 x 0.25 x 0.20 mm was used for collection

of intensity data on a “Bruker Apex II CCD” area detector diffractometer with

graphite monochromated MOKα radiation (0.71073) ω scan technique. The

programs used to solve and refine the structure were SHELXS-97, SHELXL97 and

PLATON [25-26]. The refinement was carried out by using the Full matrix least

square on F2. All non hydrogen atoms were refined anisotropically. All hydrogen

atoms have been geometrically fixed and refined with isotropic thermal

parameters. Crystallographic details are shown in Table 6.1 whereas the selected

bondlengths and bond angles are given in Table 6.2.

6.3.2 Crystal and molecular structure

Figure 6.2 (a) is an ORTEP [27] diagram that shows the crystal structure of

the 4M3MPBS compound. The B3LYP/6-31G(d,p) optimized structure of title

compound is illustrated in Figure 6.2 (b). The crystal structure of the 4M3MPBS

compound is monoclinic and space group is C2/c, M.W = 261.33,

a=14.1210(4)Å, b=14.5418(5) Å, c=13.5021(5) Å, α=90 β=98.06(10), γ=90° and

V=2745.17(16) Å3. Additional information for the structure determinations are


Table 6.1. Crystal data and structure refinement for 4M3MPBS. Empirical formula C14 H15 N O2 S Formula weight 261.33 Temperature 298(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, C2/c Unit cell dimensions a = 14.1210(4) A alpha = 90 deg. b = 14.5418(5) A beta = 98.0640(10) deg. c = 13.5021(5) A gamma = 90 deg. V olume 2745.17(16) A^3 Z, Calculated density 8, 1.265 Mg/m^3 Absorption coefficient 0.229 mm-̂1 F(000) 1104

Crystal size 0.28 x 0.25 x 0.20 mm Theta range for data collection 2.65 to 28.27 deg. Limiting indices -17<=h<=16, -15<=k<=19, -17<=l<=17 Reflections collected / unique 9162 / 3071 [R(int) = 0.0289] Completeness to theta = 25.00 98.7 % Absorption correction None Max. and min. transmission 0.9556 and 0.9386 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 3071 / 0 / 169 Goodness - of- fit on F^2 1.005 Final R indices [I>2sigma(I)] R1 = 0.0472, wR2 = 0.1365 R indices (all data) R1 = 0.0768, wR2 = 0.1585 Largest diff. peak and hole 0.256 and -0.320 e.A -̂3


Table 6. 2 Selected bond lengths and bond angles of 4M3MPBS

Parameter Experiment a Experiment B3LYP

Bond Lengths(Å) C1-C6 1.364(4) 1.369(4) 1.404 C1-C2 1.365(5) 1.358(7) 1.404 C4-C5 1.388(4) 1.388(3) 1.399 C8-C13 1.388 1.388(3) 1.399 C8-C9 1.389 1.389 1.399 C4-S1 1.753(2) 1.752(3) 1.79 N1-C8 1.414 1.433 1.433 C12-C14 1.510 1.496(4) 1.51 C1-C7 1.516 1.508(5) 1.509 S1-N1 1.616(19) 1.619(2) 1.724 N1-H1 .76 .839 1.018 C2-H2 .93 .93 1.08 O1-S1 1.424(16) 1.414(2) 1.464 O2-S1 1.434(14) 1.4335 1.468 Bond angles(°) C6-C1-C2 118.1(3) 119.4(3) 118.5 C13-C8-N1 122.1(2) 122.1(2) 120.12 O1-S1-O2 118.29(10) 118.24(12) 120.28 O1-S1-N1 109.44(11) 109.971(2) 106.61 O2-S1-N1 104.81(10 104.53(12) 111.18 O1-S1-C4 107.8(9) 107.58 109.82 C8-N1-S1 126.41 125.8(17) 118.62 N1-S1-C4 106.75 106.57(12) 99.03 Dihedral angles(°) C3‐C4‐S1‐O1 179.13(19) 179.5(2) 173.08 C5‐C4‐S1‐O2 128.15(19) 127.7(2) 138.09 C6‐C1‐C2‐C3 1.8(4) 1.5(4) ‐.296 C10‐C11‐C12‐C13 0.4(4) 0.1(5) 1.61 C8‐N1‐S1‐O1 ‐60.2(2) 59.6(3) 58.93 C8‐N1=S1‐O2 172.0(2) 172.5(2) ‐73.8 C8‐N1‐S1‐C4 56.3(2) 56.7(3) 172.873 C7‐C1‐C2‐C3 178.5 178.4(3) 178 C14‐C12‐C13‐C8 177.0(3) 176.4(3) 178

a XRD taken from Literature.


Figure 6.2a An ORTEP drawing of 4M3MPBS, with the atom numbering

Scheme. Displacement ellipsoids are drawn at the 30%

Probability level

Figure 6.2b Optimised structure of 4M3MPBS with atom numbering

obtained by DFT/B3LYP 6-31G(d,p)


157

given in Table 6.1. The optimized parameters of 4M3MPBS(bond lengths and

angles, and dihedral angles) by B3LYP method with 6-31G(d,p) as the basis set are

listed in Table 6.2 and compared with the experimental crystal structure

parameters.

The S1═O1 and S1═O2 bond distances (average = 1.429 (2) Å) are in good

agreement with those found for structures containing the sulfonyl group [28,29].

These distances have been calculated at 1.464 Å, 1.468Å using B3LYP/6-31G(d,p)

method respectively. The presence of the methyl group in the 3-position of the

phenyl ring leads to an elongation of the C12‒ C14 (methyl carbon) bond length

to1.510 (2) Å. This bond is 1.494 (2) Å in sulfonated ortho methyl aniline, in

which an methyl group is bound to the 2-position of the phenyl ring.

6.3.3 Hydrogen Bonding and Crystal Packing

The crystal structure contain intermolecular N-H···O interactions. In the

title compound, atom S1 in the molecule at (x, y, z) acts as hydrogen-bond donor,

via atoms H1 to atoms N1 at (-x,-y+1,-z+1) Figure 6.3(a). The experimental N-

H···O intermolecular contact distance valueis 2.92 Å and bond angle value is 165°.

The full geometry of intermolecular interactions is givenin Table 6.3.

6.3.4 Geometrical Structure

The molecular structure of 4M3MPBS obtained by B3LYP 6-

31G(d,p) is shown in Figure 6.2 (b). For this compound, C12-C14 (methyl carbon)

bond length calculated at 1.51Å using B3LYP/6-31G(d,p) method and the data are

shown in Table 6.2 for the optimized geometric parameters. The meta-CH3 group

of the phenyl ring can not take part in mesomeric effect. Hence the bond length of


Table 6.3 Hydrogen bond geometry(Å) of 4M3MPBS crystal D‐H‐A D‐H H‐A D…A <(DHA) N1‐H1…O2 0.77(3) 2.19(2) 2.929(2) 165(3)

C6‐H5…O1 0.93(3) 2.52(3) 2.893(3) 104(4) C10‐H13‐O1 0.93 2.46 3.106(3) 126(2) Note: D: Donor, A: Acceptor

Symmetry transformations used to generate equivalent atoms:

‐x, 1‐y, 1‐z


Figure 6.3 (a) Molecular packing diagram of 4M3MPBS

Figure 6.3(b) Linear Correlation between calculated versus experimental bond lengths


158

C-CH3 is not much affected (1.51 Å).The bond distances and angles of the phenyl

ring are comparable with those in the literature [30]. The B3LYP methods for

optimized geometric parameters (bond lengths, bond angles and dihedral angles)

are much closer to experimental data. Theoretical bond lengths vary ± .0108 Å

where comparing with the XRD data and these differences are probably due to

intramolecular interactions in the solid state. Graphic correlation between

experimental versus theoretical bond lengths is shown in Figure 6.3(b). The values

of correlation coefficient provide good linearity between calculated and

experimental bond lengths (correlation coefficient R2 of .9535). From the

theoretical values, we can find that most of the optimized bond angles are slightly

larger than the experimental values, due to the theoretical calculations belong to

the isolated molecules in gaseous phase and the experimental results belong to the

molecules in solid phase. The bond angle (O1-S-O2) varies 2.01° from XRD data.

6.4 VIBRATIONAL ASSIGNMENTS

The global minimum energy obtained by DFT structure optimization of the

compound 4M3MPBS is found to be –1145.87 a.u. 4M3MPBS belongs to C1 point

group symmetry. The compound has 33 atoms and hence possesses 93

fundamental modes of vibrations. Among them 32 stretching vibrations, 31 in-

plane bending vibrations, 30 out-of-plane bending vibrations.

The experimental FTIR spectrum and FT-Raman are shown in Figure

6.4(a) and Figure 6.4(b).Vibrational frequencies calculated at B3LYP/6-31G(d,p)

level were scaled by 0.96 [31]. As it is seen from Table 5.4, the predicted harmonic

vibration frequencies and the experimental data are very similar to each other.

Vibrational assignments have been carried out using VEDA [32] programme

combined with Gauss view software [33].


Table 6.4 Vibrational wavenumbers obtained for 4M3MPBSat B3LYP/6-31G(d,p) [(harmonic frequency cm−1), IR intensities (K mmol−1),Raman intensities (arb. units)]. Mode Nos Experimental

(cm−1)

FT-IR

FT-Raman

DFT Calculated (cm−1) (scaled

IbIR Ic

Raman Vibrational assignments PED (%)

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

3251 3068

2915

1592

1497

1402

1322

1249

3254 3054

2924

1604

1298

1185

338130973096309330733060305930563048300730022980297729212919159715881577156314751475145814441442144214281386137013691347130513001282127412411222118611631151

0.60.00.20.30.20.91.30.10.51.70.30.54.00.25.30.52.80.53.46.36.83.85.4

36.835.91.6

34.46.9

100.413.610.626.222.52.7

20.893.10.84.84.8

3.58.70.43.21.42.32.91.20.92.24.12.77.11.01.11.37.50.21.40.56.62.15.82.42.80.7

43.68.3

22.63.73.08.31.5

22.45.5

19.24.03.14.8

νNH(100) νCH(99) νCH(95) νCH(94) νCH(99) νCH(89) νCH(88) νCH(96) νCH(100) νCH(99) νCH(100) νCH(100) νCH(100) νCH(100) νCH(100) νCC(48) νCC(31) νCC(44)+ΒCCC(24) νCC(51)+ΒCCC(11) βHCC(65)+ βCCC(10) βHCC(52) βHCC(10)+ βHCH(38) βHCH(73) βHCH(75) βHCH(59) βHNC(13)+ βHCC(10)+ βHCC(38) νCC(35)+ βHCC(23) βHCH(91) βHCH(92) νCC(14)+ βHNC(36) νCC(36)+ βHCC(49) νCC(77) βHCC(91) νCC(10)+νSO(39) νCC(10)+νSO(39) νCC(28)+νNC(14)+ βCCC(11) νCC(39)+ βCCC(13) νCC(23)+ βHCC(73) νCC(10)+ βHCC(74)


40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

1095

951

894

811 781

695 657

626 566 540

1010

753

581

1135110010951082104810231022992990975974946932932916874849823817794783761735687674656622617583540512509485469431414398384346309302259243218201167

37.80.00.00.20.10.5

10.63.84.79.4

40.94.9

39.159.025.10.93.22.1

15.858.243.11.40.76.2

60.90.90.26.10.62.15.77.4

10.141.82.30.6

23.913.029.417.614.112.110.110.78.11.1

11.50.70.50.37.3

42.23.01.91.80.29.56.7

14.319.922.03.64.0

14.437.937.88.71.01.15.8

35.128.250.00.98.9

22.620.019.04.35.90.85.5

58.983.248.6

185.9277.285.4

103.265.565.758.6

νCC(16)+νNC(21)+ βHCC(39) νSO(33)+ βHCC(16) νCC(16)+νSO(12)+ βHCC(17) νCC(46)+ βHCC(39) νCC(32)+νSO(39) βHCCC(55) βHCCC(57) βCCC(75) νCC(11)+ βHCCC(57) νCC(11)+ βτCCC(58) τHCCC(40) τHCCS(48)+τHCCC(30)+τCCCC(11) τHCCC(66)+τCCCC(15) τHCCC(34)+τHCCS(42) νCC(15)+νNC(19)+ βCCC(17) τHCCC(55) τHCCC(81) τHCCC(51)+τHCCS(43) νSN(22)+τHNCC(29) τHCCC(34)+τHCCS(23) νCC(13)+βCCC(25) τHCCC(72) νCC(12)+ βCCC(24) τCCCC(62) τHCCC(19)+τCCCC(56) νSC(11)+τONOS(17) βCCC(57) νSN(22)+τHNCC(16) νCC(10)+νSC(10)+ βCCC(13) βOSO(15)+ βCSN(15) τONOS(27) νCC(30)+ βCCC(31) βOSO(30)+ βNCC(11) τCCCC(24)+τCSCC(27) τCCCC(47) βCCS(14)+ βCCC(10)+ βOSO(16) τCCCS(65)+τCCCC(10) βNCC(24)+ βCCC(27)+ βOSO(13) βCCC(51)+ βOSN(13) τCCCS(19)+τCCCC(16) βCCC(57) νSC(30)+τONOS(12) βNCC(11)+ βOSN(31)+ βSNC(12) τCCCC(51) τCCCC(57) βCCS(57)


86 87 88 89 90 91 92 93

13995594235282314

13.68.08.0

14.60.71.60.37.2

76.994.2

113.2225.260.186.647.656.7

βCCS(23)+ βCSN(24) τCCCS(13)+τNCCC(18) τCCSN(12)+τSNCC(32) τHCCC(90) βCSN(14)+ βSNC(22) τHCCC(61) τCCSN(71)+τSNCC(18) τCSNC(72)+ τβSNCC(18)


4000 3500 3000 2500 2000 1500 1000 500

Tran

smitt

ance

(arb

.uni

ts)

wavenumber cm-1

Figure 6.4a Experimental and Theoretical FTIR spectrum of 4M3MPBS

3500 3000 2500 2000 1500 1000 500

Wavenumber(cm-1)

B3LYP

Ram

an In

tens

ity(a

rb.u

nits

)

Experimental

Figure 6.4b Experimental and Theoretical 4M3MPBS

Experimental

B3LYP


159

6.4.1 N-H Vibrations

The vibrations belonging to N-H stretching [34] always occur in the region

3450–3250 cm-1. In this study, the strong band observed at 3251 cm-1 in FTIR and

weak band at 3254 cm-1 are assigned to N-H stretching vibrations. The

theoretically calculated values by B3LYP/6-31G(d,p) method at 3381 cm-1 (mode

no.1) is assigned to N-H stretching vibrations. The TED for this mode suggests

that this is a pure mode, the TED of this mode is 100 %. The N-H in-plane

bending and out of plane bending vibrations are shown in Table 6.4. The PED of

these vibrations shows that they are not in pure mode.

6.4.2 C-H vibrations

The bands around 3100-2800 cm-1 are assigned to the CH stretching vibrations in

aromatic compounds. The C-H stretching frequency of such compounds falls very

nearly in the region of 3100- 2900 cm-1 for asymmetric stretching and 2980 – 2900

cm-1 for symmetric stretching modes of vibration. They are not appreciably

affected by the nature of the substituents. In the present work, the bands observed

at 3068 cm-1 in FTIR and 3054 in FT-Raman were assigned to the C-H stretching

vibration of 4M3MPBS. The aromatic CH stretching vibrations calculated

theoretically in the region 3097-3056 cm-1 for B3LYP. The C-H in plane and out

of plane bending vibrations of the molecule were given in Table 6.4.

For methyl groups the symmetric stretching mode calculated in the range

2919-2977 cm-1, the asymmetric stretching mode lie in the region 2980-3007 cm-1.

The FTIR bands observed at 2915 in FTIR, 2924 cm-1 in FT-Raman. In B3LYP,

the modes (10-15) at 3007-2919 cm-1, represent asymmetric and symmetric CH3

stretching vibrations in 4M3MPBS. Rocking vibration of CH3 at 1163 cm-1, 1151


160

cm-1 are well comparable with theoretically calculated values. The CH3 torsional

mode was assigned at 167 and 201 cm-1 for B3LYP level respectively.

6.4.3 C-C vibrations

The ring carbon–carbon stretching vibrations occur in the region

1625–1430 cm−1. For aromatic six-membered rings, there are two or three bands in

this region due to skeletal vibrations, the strongest usually being at about

1500 cm−1. In general, the bands are of variable intensity and are observed at

1625–1590, 1590–1575, 1525–1470 and 1465–1430 cm−1. Based on these factors,

in the compound 4M3MPBS the FT-Raman band observed at 1597, 1588 and 1577

cm-1 and 1566 cm -1 assigned to aromatic C-C stretching vibrations.

6.4.4 Heavy Atoms Fundamentals Vibration

The asymmetric stretching for the SO2 has magnitude higher than the

symmetric stretching [35,36]. The symmetric and asymmetric SO2 stretching

vibrations occur in the region 1125–1150 cm-1and 1295–1330 cm-1, respectively

[37]. The intense signals appearing at 1418 and 1217 cm-1 in FTIR and 1414 and

1228 cm-1 in FT-Raman were attributed to the SO2 antisymmetric and symmetric

stretching fundamental modes for sulfamoil fluoride substance by Alvarezaetal

[38]. Dodoff et al [16] recorded the symmetric stretching mode at

1150 cm1 as strong peak, and the antisymmetric modes at 1341 and 1351 cm-1 in

infrared spectrum for N-3-Pyridinylmethanesulfonamide. In the present study, the

symmetric S-O stretching vibration was obtained at 1095 cm-1 in FT-IR spectrum

and 1185 cm-1 in FT-Raman. The bands observed at 1249 and 1322 cm-1 in FT-IR

and 1298 cm-1 in FT-Raman spectrum were assigned to antisymmetric and

symmetric S-O stretching vibrations in Table 6.4. The S-C vibrations calculated at

656 and 259 cm-1in B3LYP. The S-N vibration calculated at 617 cm-1 for B3LYP.

The bending vibrations of O-S-O and C-S-N are also given in Table 6.4.


161

6.5 FTNMR SPECTRAL ANALYSIS

The experimental 13C and 1H spectra are presented in Figure 6.5 (a) and

6.5 (b) respectively. The theoretical 13C and 1H chemical shift values (with respect

to TMS) of the title compound are generally compared to the experimental13C and 1H chemical shift values. Aromatic carbons give signals in overlapped areas of the

spectrum with chemical shift values from 100 to 150 ppm [39]. In our present

study, the title molecule also falls with the above literature data.

In the 1H NMR spectrum, a singlet at 2.36 ppm indicates three protons of

the methyl group of the tosyl ring and 2.27 ppm indicate the three protons of the

methyl group of the methylphenyl ring. The above said, methyl groups protons are

calculated in the range of 1.66, 1.71 and 2.01 ppm for B3LYP. The nine aromatic

protons of methylphenyl and tosyl rings are appeared as multiplet in the range of

6.91-7.74 ppm and are calculated in the range of 6.29-8 ppm for B3LYP. The N-H

group of the metatoluidine is responsible for the appearance of broad singlet at 6.9

ppm and calculated as 5.88 ppm for B3LYP.

In the 13C NMR spectrum, the methyl carbon of the tosyl group and

metatoluidine group give signal at 21.55 ppm, 21.35 ppm calculated as 10.68 ppm

and 10.18 ppm. The twelve aromatic carbons of tosyl and metatoluidine group are

appeared as multiplet in the range of 118.19-143.82 ppm and are calculated in the

range of 113-134 ppm for B3LYP. The signal at 143.82 ppm is assigned to the

carbon of tosyl ring which is bonded with methyl group, calculated as 134 ppm.

The signal at 139.30 ppm is assigned to the carbon of methylphenyl ring which is

bonded with methyl group, calculated as 127 ppm. The signal at 136.56 ppm is

assigned to the carbon of methylphenyl ring which is bonded with NH group,

calculated as 124 ppm. The signal at 136.11 ppm is assigned to the carbon of tosyl


Table 6.5

The chemical shift in 1H NMR and 13CNMR spectrum of 4M3MPBS crystal

Spectrum Experimental (CDCl3) signal at δ(PPM)

B3LYP Calculated Chemical shift at δ(PPM)

Group Identification

1H NMR 2.364 1.66, 1.71, 2.01 3 protons of the Methyl group of phenyl ring

6.91‐7.74 6.29‐8 Phenyl protons 6.9 5.88 N‐H Proton 13C NMR 21.55 10.68 methyl carbon of the tolyl group 21.35 10.18 C 12 (NO2 attached carbon) 143.82 134 C4 (methyl group attached carbon) 139.30 127 C8 (N‐H attached carbon) 136.56 124 C1(SO2 attached carbon) 136.11 123 C9 129.66 116 C10 129.06 116, 115 Meta carbons of tolyl ring 127.31 114 Ortho carbons of tolyl ring 125.95 115 C19 121.93 114 C25 118.19 113 C20 76.83‐77.34 79.86 Carbon of the solvent CDCl3


Figure 6.5a H1 NMR spectrum of 4M3MPBS

Figure 6.5b C13 NMR spectrum of 4M3MPBS


162

ring which is bonded with sulfonyl group, calculated as 123 ppm. The Meta

carbons of the tosyl ring are responsible for the signal at 129.66 ppm, calculated as

116ppm. The ortho carbons of the tosyl ring are responsible for the signal at

129.06 ppm, calculated as 114 ppm. 127.31 ppm, 125.95 ppm, 121.93 and

118.19 ppm chemicalshifts values are due to different positions of tosyl and phenyl

ring which are given in the Table 6.4. The above said relevant calculated 13C

chemical shifts are listed in the table. (see ORTEP diagram for numbering of

atoms). A Signal at 76-78 ppm indicates the carbon atom of the CDCl3 (solvent),

calculated as 79 ppm. As it is seen from table, calculated 1H and 13C chemical

shifts values of the title compound are generally agreement with the experimental 1H and 13C chemical shifts data.

6.6 NATURAL BOND ORBITAL (NBO) ANALYSIS

Natural (localized) orbital is used in computational chemistry to calculate

the distribution of electron density in atoms and in bonds between atoms. They

have the ‘‘maximum occupancy character’’ in localized 1-center and 2-center

regions of the molecule. Natural bond orbital (NBO) includes the highest possible

percentage of the electron density, ideally close to 2.000, providing the most

accurate possible ‘‘natural Lewis structure’’ of the wave function. A useful aspect

of the NBO method is that it gives information about interactions in both filled and

virtual orbital spaces which could enhance the analysis of intra- and intermolecular

interactions. The second-order Fock matrix is carried out to evaluate the donor–

acceptor interactions in the NBO analysis [40]. The interactions result is a loss of

occupancy from the localized NBO of the idealized Lewis structure into an empty

non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2)

is associatedwith the delocalization i,j is estimated as


163

E(2) = ∆Eij = qi ⎟⎟⎠

⎞⎜⎜⎝

⎛

− )(),( 2

ij

jiFεε

where qi is the donor orbital occupancy, Ei and Ei are diagonal elements and F(i, j)

is the off diagonal NBO Fock matrix element. Natural bond orbital analysis has

been carried out to explain the charge transfer or delocalization of charge due to

the intra-molecular interaction among bonds, and also provides a convenient basis

for investigating charge transfer or conjugative interaction in molecular systems.

Some electron donor orbital, acceptor orbitaland the interacting stabilization

energy resulting from the second-order micro disturbance theory is reported [41].

The larger the stabilization energy value, the more intensive is the interaction

between electron donors and electron acceptors, i.e. the more donating tendency

from electron donors to electron acceptors and the greater the extent of conjugation

of the whole system. Delocalization of electron density between occupied Lewis-

type (bond or lone pair) NBO orbitals and formally unoccupied (antibond or

Rydberg) non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor

interaction.

NBO analysis has been performed on the molecule at the DFT/B3LYP/

6-31G(d,p) level in order to elucidate the conjugation, hyperconjugation and

delocalization of electron density within the molecule. The intra molecular

interaction are formed by the orbital overlap between (σ and π (C–C, C-H and CN)

and σ*and π *(C-C, C-H and C-N)) bond orbital which results intra molecular

charge transfer (ICT) causing stabilization of the system. These interactions are

observed as increase in electron density (ED) in C–C anti bonding orbital that

weakens the respective bonds. The electrondensity of conjugated double as well as

single bond of the aromatic ring (~1.9e) clearly demonstrates strong delocalization

inside the molecule. The strong intramolecularhyperconjugationinteraction of the σ


164

(C –C) to the π*(C–C) bond in the ring leads to stabilization of some part of the

ring as evident from Table 6. For example, the intra molecular hyper conjugative

interaction of σ (C1–C2) distribute to σ * (C1–C6) leading to stabilization of ~3.0

kJ/mol. This enhanced further conjugate with anti-bonding orbital of π*(C3–C4)

and (C5–C6), leads to strong delocalization of 24.73 and 17.42 kJ/mol

respectively. The magnitude of charges transferred from (LP(2)O17)→(C4-S15)

and (LP(1)N18)→(S15-O16) show that stabilization energy of about ~16 KJ/Mol

and ~ 8 KJ/Mol respectively. The delocalization of electron π*(C3-C4) and π*(C3-

C4)to π*(C5-C6) and π*(C1-C2) with enormous stabilization energy of about ~

209 KJ/moland 176.19 KJ/mol respectively.

6.7 NON-LINEAR OPTICAL EFFECTS

The calculations of the mean linear polarizability (αtot) and the mean first

hyperpolarizability (βtot) from the Gaussian output have been explained in detail

previously in chapter one. DFT has been extensively used as an effective method

to investigate the organic NLO materials [42]. The total molecular dipole moment

(μtot), linear polarizability (αtot) and first-order hyperpolarizability (βtot) of the title

compound were calculated at the B3LYP/6−31G(d,p) level. The calculated values

of μtot, and βtot of urea are 1.46 D and 6.06 × 10−31 cm5/esu. Urea is one of the

prototypical molecules used in the study of the NLO properties of molecular

systems. Therefore it was used frequently as a threshold value for comparative

purposes. The values of μtot and βtot of 4M3MPBS are 3.53 D and 20.47 × 10−31

cm5/esu obtained at the same level. Theoretically, the firstorder hyperpolarizability

of the title compound is of 3.37 times magnitude of urea. According to these

results, the title compound is a good candidate of NLO material.


Table6.6. Second order perturbation theory analysis of Fock matrix in NBO basis.

Donor(i) Type ED(e) Acceptor Type ED(e) E(2)a

(KJ/mol) E(j)‐

E(i)b(a.u) F(i,j)c (a.u) C1‐C2 σ 1.978 C1‐C6 σ* 0.0213 3.12 1.27 0.056

C1‐C11 σ* 0.0156 1.18 1.08 0.032 C2‐C3 σ* 0.0172 2.73 1.26 0.052

C3‐H8 σ 1.938 C22‐C25 σ* 0.3530 5.11 0.57 0.052 C22‐H26 σ* 0.0331 13.87 1.1 0.111

C4‐C5 σ 1.976 C3‐C4 σ* 0.0251 4.56 1.27 0.068 C4‐S15 σ 1.965 N18‐H19 σ* 0.0092 1.2 1.18 0.034

S15‐O16 σ* 0.1652 4.37 1 0.061 S15‐O17 σ* 0.1443 3.62 1 0.055 S15‐N18 σ* 0.2651 2.53 0.82 0.043

C1‐C2 π 1.639 C3‐C4 π* 0.3988 25.73 0.26 0.074 C5‐C6 π* 0.3031 17.42 0.28 0.063

C3‐C4 π 1.684 C1‐C2 π* 0.3286 15.02 0.3 0.06 π C5‐C6 π* 0.3031 21.59 0.29 0.071

C5‐C6 π 1.659 C1‐C2 π* 0.3286 23.02 0.28 0.072 C3‐C4 π* 0.3988 17.49 0.27 0.062

C20‐C21 π 1.675 C22‐C25 π* 0.3529 19.03 0.29 0.067 C23‐C27 π* 0.3262 18.96 0.29 0.066

C22‐C25 π 1.654 C20‐C21 π* 0.3713 21.29 0.28 0.069 C23‐C27 π* 0.3529 18.51 0.28 0.065

C23‐C27 π 1.986 C20‐C21 π* 0.3713 20.66 0.27 0.067 C23‐C27 π 1.972 C22‐C25 π* 0.3529 22.23 0.28 0.071 C3‐C4 π* 1.817 C1‐C2 π* 0.3286 176.19 0.02 0.082 C3‐C4 π* 1.817 C5‐C6 π* 0.3031 209.36 0.01 0.078 C20‐C21 π* 1.687 C22‐C25 π* 0.3714 266 0.01 0.079 LP(2)O17 1.671 C4‐S15 π* 0.1878 16.34 0.43 0.075 LP(2)O17 0.586 S15‐O16 π* 0.1652 13.99 0.56 0.079 LP(1)N18 1.908 S15‐O16 π* 0.1652 8.32 0.65 0.067


Table 6.7

The electric dipolemoment(D), Polarizability and first hyperpolarizability of 4M3MPBS

a.u esu(x10‐24) a.u (esux10‐33)αxx 190.9947 Βxxx ‐26.7880 ‐231.429αxy 3.59455 Βxxy ‐30.4430 ‐263.006αyy 129.6996 Βxyy ‐63.0749 ‐544.915αxz 12.5837 Βyyy ‐37.9007 ‐327.435αyz ‐33.96457 Βxxz 84.2041 727.465αzz 159.8123 Βxyz 16.6616 143.944αtotal Βyyz 34.10269 294.622µx ‐2.572145 Βxzz ‐7.61852 ‐65.818µy ‐0.922806 Βyzz ‐22.9659 ‐198.409µz 0.6422984 Βzzz ‐77.4277 ‐198.409µ 2.4853 Βtotal 2047.1953


165

6.8 MULLIKEN ATOMIC CHARGES

Mulliken atomic charge calculation plays an important role in the

application of quantum mechanical calculations to molecular systems [43]. The

calculated Mulliken charge values of 4MNBS are listed in Table 6.6. The charge

distribution structure is shown in Fig 6. The Mulliken atomic charge analysis of

4MNBS shows that the presence of two oxygen atoms in the sulphonamide moiety

(O16 = −0.5307); (O17=−0.5163) imposes positive charge on the sulfur atom

S15 = 1.1423. However, the carbon atoms C2, C3, C4, C5, C6, C15, C21, C22,

C23, C24, and C26 posses small negative charges, whereas carbon atoms C1, C20,

and C25 posses positive charge due to large negative charge (-0.633413) of N18.

Moreover, there is no difference in charge distribution observed on all hydrogen

atoms except the H19 and methyl group hydrogens (H32, H33 and H34). The large

positive charges on H19 (0.3056) and methyl group hydrogens due to large

negative charge accumulated on the N18 atom and C11 and C31 (methyl carbons)

atom respectively.

6.9 MOLECULAR ELECTROSTATIC POTENTIAL (MEP)

The molecular electrostatic potential, V(r), at a given point r (x,y, z) in the

vicinity of a molecule, is defined in terms of the interaction energy between the

electrical charge generated from the molecule electrons and nuclei and a positive

test charge (a proton) located at r. The molecular electrostatic potential (MEP) is

related to the electronic density which is a very useful descriptor for determining

sites for electrophilic attack and nucleophilic reactions as well as hydrogen-

bonding interactions [44,45]. To predict reactive sites for electrophilic and

nucleophilic attack for the title molecule,MEP is calculated at the B3LYP/

6-31G(d,p) optimized geometry. The negative (red) regions of MEP are related to


Table 6.8 Mulliken Charges for 4M2MPBS

Atom with numbering charges C1 C2 C3 C4 C5 C6 H7 H8 H9 H10 C11 H12 H13 H14 S15 O16 O17 N18 H19 C20 C21 C22 C23 C24 H25 C26 H27 H28 H29 C30 H31 H32 H33

0.101282-0.10803-0.0409

-0.14436-0.08779-0.104450.0792730.0402280.1310390.094989-0.375670.120246

0.13830.1225591.150793-0.53711-0.51531-0.657570.3013440.0782220.137515-0.08754-0.12342-0.100590.173235-0.071580.0904320.0895620.090784-0.370830.18205

0.0899040.113398


Figure 6.6 Mulliken Charge distribution of 4M3MPBS


Figure 6.7 Molecular Electro static potential (MEP) of 4M3MPBS


166

electrophilic reactivity and the positive (white) regions to nucleophilic reactivity

are shown in Fig. 8. The negative regions are mainly localized on the O8 and O9

oxygen atoms. A maximum positive region is localized on the hydrogen atoms

indicating a possible site for nucleophilic attack. The MEP map shows that the

negative potential sites on electronegative atoms as well as the positive potential

sites are around the hydrogen atoms. The MEP provides a visual representation of

the chemically active sites and comparative reactivity of the atoms.

6.10 ELECTRONIC SPECTRAL ANALYSIS

The time dependent density functional method (TD-DFT) method is used

with B3LYP function and 6-31G (d,p) basis set for vertical excitation energy of

electronic spectrum. On the basis of a fully optimized ground state structure, the

electronic spectrum of 4M3MPBS was computed in the gas phase environment

using TD-DFT method. The experimental UV–Vis spectrum is shown in Figure

6.9. Molecules allow π-π* transition in the UV–Vis region. TDDFT calculations

predict three transitions in the UV–Vis region for 4M3MPBS molecule. This

calculations (for vertical transition) agrees well with the experimentally observed

π-π* band. It is mainly described by one electron excitation from the highest

occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital

(LUMO).

6.11 FRONTIER MOLECULAR ORBITAL ANALYSIS

Molecular orbital and their properties like energy are very useful to the

physicists and chemists and their frontier electron density used for predicting the

most reactive position in p-electron system and also explained several types of

reaction in conjugated systems [46].


Figure 6.8 UV-VIS absorption spectrum of 4M4MPBS


167

Surfaces for the frontier orbitals of 4M3MPBS are shown in Fig. 8. The

HOMO is delocalized over the tolyl ring, NH-SO2 group and partially on tosyl ring

except methyl groups. LUMO is placed over the entire benzene rings except NH-

SO2 group. The HOMO - LUMO transition implies an electron density transfer to

tosyl ring from 3-methyl aniline ring through NH-SO2 group. The computed

energy values of HOMO and LUMO are -6.585eV and -1.095eV respectively. The

energy gap value of 4M3MPBS molecule is 5.51eV in gas phase. Lower value in

the HOMO and LUMO energy gap explains the eventual charge transfer

interactions taking place within the molecule. The frontier molecular orbitals are

mainly composed of p atomic orbital, so, electronic transitions from the HOMO to

the LUMO are mainly derived from the electronic transitions of π-π*.

The quantum chemical reactivity descriptors of molecules such as hardness,

chemical potential, softness, electronegativity and electrophilicity index as well as

local reactivity have been calculated. The computed quantum chemical descriptors

based upon DFT calculations are depicted in Table 6.9.

6.12 THERMAL ANALYSIS

The first endothermic peak observed at 108.3°C is attributed to the melting

of the 4M3MPBS crystal. At this melting point endotherm, no weight loss was

observed in the TG curve. The weight loss starts around 205°C and the major

weight loss (91%) corresponding to the decomposition of 4M3MPBS was

observed at 340°C, which takes place over a large temperature range (205-340°C)

where almost all the compound decompose as its gaseous products. The

endothermic peak corresponding to the major weight loss was observed at 340°C

in the DTA curve. The 4M3MPBS is chemically stable upto 205°C, above which

temperature the sample gradually decomposes. No exothermic or endothermic


LUMO plot

Energy Band Gap=5.49 eV

EHOMO = ‐6.58 eV

HOMO Plot

ELUMO = ‐1.09 eV

Figure 6.9 HoMO-LUMO surfaces of 4M3MPBS


Figure 6.10 TGA and DTA of 4M3MPBS


168

peak was observed below the melting point endotherm, indicating the absence of

any isomorphic phase transition in the sample.

6.13 CONCLUSION

In the present work, the optimized molecular structure of the stable

conformer, chemical shifts and electronic properties, vibrational frequencies,

intensity of vibrations of 4M3MPBS have been calculated by DFT method using

B3LYP/6-31G(d,p) basis set. The optimized geometric parameters (bond lengths,

bond angles and dihedral angles) are theoretically determined and compared with

the experimental results. The vibrational FTIR and FT-Raman spectra of the

4M3MPBS are recorded and on the basis of agreement between the calculated and

experimental results, assignments of all the fundamental vibrational modes of the

4M3MPBS were made explicitly based on the results of the PED output obtained

from VEDA. The electronic properties are also calculated and compared with the

experimental UV–Vis spectrum. The energies of important molecular orbitals and

the λmax of the compound are also evaluated from TD-B3LYP method with 6-

31G(d,p) basis set. When all theoretical results scanned, they are showing good

correlation with experimental XRD data. The differences between the observed

and scaled wavenumber values of most of the fundamentals are very small.

Therefore, the assignments made at DFT level of theory with only reasonable

deviations from the experimental values seem to be correct. The NBO analysis

indicates the intramolecular charge transfer between the bonding and antibonding

orbitals.


169

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