chapter 8 spectroscopic and molecular structure...

CHAPTER 8

SPECTROSCOPIC AND MOLECULAR STRUCTURE

INVESTIGATION OF 4-METHYL-N-(4-NITROPHENYL)

BENZENE SULFONAMIDE BY DFT METHOD:

A COMBINED EXPERIMENTAL AND THEORETICAL STUDY

8.1 INTRODUCTION

Para-nitroaniline, a well known donor–acceptor system, with relatively

high nonlinearity was commonly used to design and synthesize molecules with

high electro-optic coefficients. It has attracted attention because of the specific

effects of an electron withdrawing nitro group and an electron donating amino

group being in para position at an aromatic ring system, showing a great nonlinear

susceptibility and making this molecule interesting for nonlinear optics [1].

Chis et al [2] reported Experimental (FT-Raman, SERS) and theoretical

(DFT) study on para-nitroaniline. Tanaka et al [3] have investigated the Raman

spectra of para nitroaniline in acetonitrile solution. Panunto et al [4]. studied the

crystal structure of para nitroaniline (monoclinic P21/n). Gustavo Pozzi et al [5]

described the use of crystal vibrational modes in the estimation of the anisotropic

displacement parameters of hydrogen atoms in

para-nitroaniline. Dhanya et al [6] reported ground state and excited state dipole

moments of alkyl substituted para-nitroaniline derivatives. G.C.Yang [7] reported

hyperpolarizabilities of para nitro aniline based on TDDFT–SOS method.

Katarzyna Piela et al [8] reported molecular motions contributions to

optical nonlinearity of N-benzyl-2-methyl-4-nitroaniline studied by temperature-

dependent FT-IR, 1H NMR spectroscopy and DFT calculations.

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Experimental and theoretical study of the structure of N,N-dimethyl-4-

nitroaniline derivatives, vibrational spectra of the 2,6-dibromo-4-nitroaniline (2,6-

DB4NA) and 2-(methylthio)aniline have been studied by applying the DFT

calculations based on Becke3-Lee-Yang-Parr (B3LYP) level with 6–31G*[9].

4-Nitrobenzenesulfonyl groups as activating groups have also been

frequently used for the preparation of secondary amines both in solution- and

solidphase synthesis [10-13]. The X-ray crystallographic structure of

2-nitrobenzene sulfonamide was analyzed by Cheng et al. [14]. Tremayne et al.

[15] investigated the structures of three substituted arenesulfonamides which are 2-

toluenesulfonamide, 3-nitro benzene sulfonamide and 4-nitro benzene Sulfonamide

from X-ray powder diffraction data using the differential evolution technique and

refined by the Rietveld method. The single-crystal X-ray analysis of 4-nitro

benzene sulfonamide was performed by Zhou et al. [16]. De Benedetti et al and

M.M. Pomerantz et al reported FTIR and NMR spectra of 4-nitro benzene

sulfonamide [17,18]. M. Karabacak et al, studied spectroscopy studies of some

benzenesulfonamide derivatives by abinitio and DFT calculations [19, 20].

Derivatives of para-methyl-(para-nitrophenyl)benzene sulfonamide have

been used as starting materials for drugs, such as antagonists of the neurotensin

receptors [21] and microbicide compositions for agriculture and horticultural use

[22]. In addition, it has also been used to prepare dyes [23].

With the aid of above seen literatures, it is clear that there is no quantum

mechanical analysis on this 4M4NPBS molecule. Hence, a detailed vibrational

analysis has been carried out here for knowing the vibrational wavenumbers,

geometrical parameters, modes of vibrations, dipole moment, rotational constants,

atomic charges and other thermodynamic parameters of this molecule. These


196

parameters were investigated using B3LYP calculations with 6-31G(d,p) basis set.

Specific scale factors were also used and employed in the predicted frequencies.

8.2 SYNTHESIS

Para Nitroaniline (6.9 gm), Triethylamine (4 ml) were dissolved in acetone

(8 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

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

water and then with petroleum ether solution (In the synthesis of the 4M4NPBS

reported earlier [24], pyridine was used as a catalyst and 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 8.1.

8.3 SINGLE CRYSTAL X-RAY DIFFRACTION ANALYSIS

8.3.1 Crystal structure Determination

A crystal with dimensions of 0.30 x 0.20 x 0.20 mm was used for

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

diffractometer with graphite monochromatic 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.


Figure 8.1 Pathway synthesis of 4M4NPBS

CH3

SO2Cl

+

NH

CH3

SO2NHNO2

ACETONE

︵C 2H5 ︶3N2

NO2


197

8.2 CRYSTAL STRUCTURE ANALYSIS

The ORTEP [27] diagram of the title molecule showing 30% Probability

displacement ellipsoids is shown in Figure 2(a). From the single crystal analysis, it

was observed that the crystal belongs to monoclinic system with space group,

p21/C. Lattice parameters have been determined as a = 13.77 (13)Å, b=8.21(7)Å, c

= 11.93(10) Å, α = 90 o β= 103 o γ = 90o and the volume of the unit cells is found

to be 1314.5(4) Å3. In the crystal structure of the title compound C13H12N2O4S, the

mean plane distance between the dihedral angles (C6-C1-C2-C3) and (C12- C7-

C8-C9) of the nitrophenyl and tolyl ring is 86.14(2)⁰. This shows their non

coplanar conformation. This is in Contrast with the near coplanar conformation

reported for the crystal structure of 4-[(2-hydroxy-benzylidene)-amino]-N-(5-

methyl-isoxazol-3-yl)-benzenesulfonamide [28]. All the Caro-Caro bond lengths are

comparable to the reported mean values of Caro-Caro =1.380Å [29]. The atoms

around the sulphonamide, “S” atom in 4M4NPBS are arranged in a slightly

distorted tetrahedral configuration. The largest deviation is in the angle

O (2)-S (1)-O (1) of 120(3)°, but it conforms to the non-tetrahedral arrangement

commonly observed in sulfonamides [30,31]. The bond angle N1–S1–C1 of

106.04(9)° is correspondingly smaller than the tetrahedral value of 109° [32]. The

S1-C1 distance of 1.7547(13) Å is normal single bond values and agrees well with

those observed in other sulfonamides [33]. The torsion angle τ(C-S-N-C) defining

the conformation of the sulfonamide group is reported to lie in the range 60-90⁰

[34]. In the present crystal structure, the torsion angle

τ1 (C1-N1-S1-C7) is 65.94(14)°. The position of the methyl group C13 is defined

by the torsion angles τ1 (C13-C10-C11-C12) and τ2 (C8-C9-C10-C13) are

179.86(14)° and 178.93(16)° respectively. The molecules in the unit cell are

related to each other by inversion. In each molecule the tolyl ring and phenyl rings

are orthogonal to each other. In fact the phenyl ring is deviated from the planar


Table 8.1 Selected bondlengths and bondangles of 4M4NPBS

Parameter Experiment a Experiment B3LYP

Bond Lengths(Å) S1-O1 1.426(4) 1.426(11) 1.463 S1-O2 1.423(5) 1.429(12) 1.462 S1-N1 1.632(4) 1.636(13) 1.703 S1-C7 1.754 1.759(15) 1.788 O3-N2 1.216 1.214(18) 1.232 O4-N2 1.214(2) 1.222(17) 1.232 N1-C1 1.408 1.461(17) 1.398 N2-C4 1.453 1.411(17) 1.461 N1-H1 0.86 0.86(5) 1.013 C1-C6 1.391(19) 1.384(19) 1.405 C1-C2 1.394 1.375(2) 1.399 C7-C12 1.381 1.388(2) 1.398 C7-C8 1.383(16) 1.378(2) 1.393 C10-C13 1.499(14) 1.5(2) 1.508 Bond angles(°) O1S1O2 120 (3) 120(7) 122.6 O1S1N1 104.32(2) 104.2(7) 109.86 O1-S1-C7 108.35(10) 108.08 (7) 107.84 O2-S1-N1 109.04(11) 109.04(7) 102.11 O2-S1-C7 108.24(10 108.5 (7) 109.11 N1-S1-C7 106.04(9) 106.06(7) 103.91 S1-N1-C1 126.63 126.64(10) 128.68 O3-N2-O4 122.33 122.52(13) 124.45 O3-N2-C4 119.02 118.83(13) 117.81 O4-N2-C4 118.63 118.62(12) 117.73 N1-C1-C6 122.35 118.62(12) 122.94 N1-C1-C2 117.34 117.44(12) 117.62 Dihedral angles(°) O1S1N1C1 179.76 ‐179.7(12) 163.19 O2S1N1C1 50.4 ‐50.32(14) 32.03 C7S1N1C1 ‐65.94 65.85(13) ‐83.11 N1S1C7C8 122.52 ‐122.62(13) 116.23 O1S1C7C8 ‐125.97 125.89(13)) ‐135.34 O2S1C7C8 5.65 5.81(14) ‐0.34 O4N2C4C3 1.41 1.6(2) 0.156 O3N2C4C5 2.51 2.2(2) 0.156 C14‐C12‐C13‐C8 177.0(3) 176.4(3) 178


Figure 8.2(a) An ORTEP drawing of 4M4NPBS, with the atom numbering Scheme.

Displacement ellipsoids are drawn at the 30% Probability level

Figure 8.2(b) Optimised structure of 4M4NPBS with atom numbering obtained by

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


198

configuration by 0.03-1.51º, see Table 2. The nitro group is found out of plane by

4.0º, see Table 8.1.

8.3.3 Hydrogen Bonding and Molecular Packing

The crystal packing is stabilized by weak intermolecular

N-H…O interaction. An N-H-O bond links the molecules into infinite chains

running along the diagonal of the crystal plane is shown in Figure.3. The amino

nitrogen N1-H is involved in intermolecular interaction with nitro oxygen. The

amino nitrogen N1-H acts as donor with nitro oxygen O3 of symmetry related x, y,

z molecule. The weak inter and intramolecular interactions (N1-H1-O3), (C3-H3-

O4), (C5-H5-O1), (C6-H6-O2) and (C8-H8-O2) of the title compound obtained by

XRD are shown in the Table 8.2.

Several researchers (35, 36) have explained the changes in the frequency or

bond length of the C-H bond on substitution due to a change in the charge

distribution on the carbon atom of the benzene ring. The substituents may be either

of the electron withdrawing type (F, Cl, Br, NO2, etc) or electron donating type

(CH3, C2H5, NH2, etc). The carbon atoms are bonded to the hydrogen atoms with

σ bond in benzene and substitution of a NO2 group for hydrogen reduces the

electron density at the ring carbon atom.

The C-N bond length (1.4535) for 4M4NPBS (para nitro derivative) is

slightly lesser (1.4686) than that of the 4M3NPBS (meta nitro compound) because

of the meso meric effect operating in the para compound. Similarly the C-N bond

of C-NH2 is slightly decreased (1.413 for 4M3NPBS & 1.4080 for 4M4NPBS

compound) in length because of the same effect. Such a mesomeric effect is not

possible for the 4M3NPBS.


Table 8.3 Hydrogen bond geometry(Å) of 4M4NPBS crystal D‐H‐A D‐H H‐A D…A (DHA) ° iN1‐H1…O3 0.86(3) 2.3 2.96(19) 135

iC3‐H3…O4 0.93(3) 2.49 3.2(2) 133 iiC5‐H5…O1 0.93(3) 2.54 3.46(18) 171 iiiC6‐H6...O2 0.96(3) 2.36 3.01(2) 127 iNote: D: Donor, A: Acceptor

Symmetry transformations used to generate equivalent atoms: i, x, ‐1+y, z ii, ‐x, ‐1/2+Y, ‐1/2‐z iii, x, 1+y, z


Figure 8.3(a) Molecular Packing diagram of 4M4NPBS

Figure 8.3(b) Plot of Calculated Versus Experimental bond lengths


199

8.3.4 Geometrical Structure

The optimized geometry was obtained by the DFT levels of theory with 6-

31G(d,p) basis set [37-41 ] .The molecular structures of the title compounds with

numbering schemes for the atoms are given in Figure 8.2(b). At C1 position, the

bond angles N1–C1–C6, N1–C1–C2 and C2–C1–C6 are 122.94°, 117.62° and

120.64° respectively for B3LYP. These bond angles are in agreement with the

XRD data. This asymmetry in angles reveals the interaction between NH group

and phenyl ring. Further, the results of our calculations showed that S1–O1 and

S1–O2 bonds show typical double bond characteristics and all other bond lengths

fall within the expected range. The experimental bond lengths are slightly shorter

than that of theoretical values. Theoretical bond lengths vary ± .071 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 8.4. The values of

correlation coefficient provide good linearity between calculated and experimental

bond lengths (correlation coefficient R2 of .9866). It is observed 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 2.6° and (O3-N2-O4) deviates 2.12° from XRD data. In spite of the

differences, calculated geometric parameters represent a good approximation and

they are the bases for calculating other parameters such as vibrational frequencies

and thermodynamic properties.


200

8.4 VIBRATIONAL ASSIGNMENTS

The harmonic vibrational frequencies and intensity of the vibrational bands were

calculated by the DFT levels of theory with 6-31G(d,p) basis set. The detailed

interpretation of the vibrational spectra of 4M4NPBS has been made using VEDA

[42 ].

8.4.1 N-H Vibrations

As it is seen in Table 8.3, the N–H stretching mode, calculated as

3456 cm-1 is observed at 3436cm-1 in the FTIR spectrum. This difference between

experimental and calculated N–H stretching vibration (20 cm-1) can be due to

N–H–O strong intermolecular hydrogen bond which has not been taken into

consideration in the calculation. In the literature, some N-H stretching modes

observed experimentally for the different substituent sulfonamide are 3273, 3343

and 3284 cm-1 [43]. The N-H in-plane bending vibration is expected near

1400 cm-1. This vibration is usually masked by the strong intense band of CH3

asymmetric bending or SO2 asymmetric stretching. In the present case, 1403 cm-1

in the FTIR spectrum, 1433, 1369 and 1210 cm-1 theoretically are due to N-H in-

plane bending vibration. The modes 73 and 75 having wavenumbers 385 and 317

cm-1 are calculated to N-H out of plane bending vibration.

8.4.2 C-H Vibrations

Normally, the C-H stretching vibrations are observed around

3100-3000 cm-1 in aromatic molecules which is a ready identification of the

benzene structure [45, 46]. This must be due to one symmetric and two asymmetric


Table 8.4 Vibrational wavenumbers obtained for 4M4NPBS at 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 40

3441 3288

3057

2922 1628 1598

1492

1403

1333

1160

1084

3075

2927

1587

1525

1476

1384

1318

1256

1163

1097

1032

3456312531173112309730893064306130613010298129231598158915881563154614771475144514401433138413711369133813151300128812821264121011861167116511021097109410891046

0.040.000.010.050.150.300.410.390.290.270.070.181.520.720.352.650.549.250.650.410.041.721.001.917.63

10.5129.361.030.73

22.156.241.782.546.37

32.1513.230.263.947.031.06

1.51.61.80.10.10.20.10.10.20.40.20.51.10.40.60.50.12.80.20.10.20.30.10.10.40.41.81.01.11.61.10.10.10.67.61.50.90.40.10.9

νNH(100) νring2CH(100) νring2CH(98) νring2CH(99) νring1CH(95) νring1CH(93)

νring1CH(95) νring2 CH(98) νring1CH(92) νmethylCH(97) νmethylCH(100) νmethylCH(100) νON(34)+νring2CC(32) νring2CC(43) νring1CC(30) νCCring1(52)+βring2CCC(11) νON(54)+νring2CC(26) βHCC(57) βring1HCC(63) βring2HCH(72) βring1HCH(78) νCC(27)+ βHNC(25)+βmethylHCC(10) νCC(35))+ βmethylHCC(23) βring2HCH(92) νring2CC(30)+ βHNC(35) νON(71)+ βONO(11) νring2CC(41) νring1CC(55) νring2CC(31)+ βHCC(31) βring1HCC(74) νNC(19)+νSO(37)+ βring1HCC(24) νring1CC(12)+νNC(20)+ βHNC(20) νring2CC(49)+ βCCC(12) βring1HCC(53) νring1CC(10)+ βmethylHCC(71) Νring1CC(11)+νSO(12)+ βring1HCC(28) νring2CC(10)+ βring2HCC(40) νSO(32)+ βring1HCC(10) Νring2CC(33)+νNC(20)+ βring2HCC(16) Νring1CC(33)+νSO(38)


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 86

907 883 813

760

677

565

939

812

756

657

585 522

488 450

316

285

250

1024991986974948942934930856829822817791790789766726693668654629621610550515512488469432405400393385328317302280262249223173155119946965

12.5551.560.050.020.370.090.270.201.561.99

25.0219.5627.594.05

16.820.813.070.86

23.2421.932.268.265.05

41.87100.2111.060.102.246.961.842.542.78

22.3522.670.095.11

45.0220.753.833.182.492.051.702.100.360.24

11.12.00.20.10.70.00.30.10.20.02.9

17.55.02.13.20.90.92.69.3

17.30.30.53.5

12.8100.1

0.87.50.41.63.53.30.30.31.21.4

15.556.70.7

43.718.212.817.214.716.614.812.9

βmethylHCH(15)+�ring1HCCC(49) βring1CCC(71) βring2CCC(75) τring2HCCC(48) τHCCS(48)+ τring1HCCC(30)+ τCCCC(13) τring2HCCN(67)+ τring2NCCC(16) τring2HCCN(71)+ τring2HCCC(16) τring1HCCC(39)+ τHCCS(41) νCC(10)+νNC(12)+νSN(15)+ΒCCC(20) νSN(16)+ βONO(34) τHCCS(43)+ τHCCC(40) τring2HCCC(53) τHCCS(33)+ τring2HCCC(30) τring2HCCC(68)+ τHCCN(29) Νring1CC(13)+ βring2CCC(24) νSN(13)+ βring2CCC(12) τCCCC(17)+ τOCON(52)+ τNCCC(12) τring1CCCC(71) τring2CCCC(66)+ τOCON(18) νNC(16)+ βONO(34)+ βCCC(12) νCC(11)+νSC(17)+ βCCC(14) βring1CCC(68) βring2CCC(46) βOSO(24)+ βNSC(11) βONC(29)+ βOSO(11)+ τONOS(17) βONC(29)+ τONOS(17) τCCCN(19)+ τring1CCCC(37)+ τNCCC(15) βOSO(11)+ τring1CCCC(23)+ τSCCC(13) νNC(17)+ τONCS(23) τring2HCCC(11)+ τring1CCCC(64) τring1HCCC(11)+ τring2CCCC(60) βCCC(15)+ βSCC(12)+ τONCS(11) τring2HNCC(58) βCCN(11)+ βCCC(34)+ τONCS(11) βOSO(13)+ βNSC(13)+ τHNCC(12) βring2CCC(17) βNCC(12)+ τCCCN(14)+ τNCCC(11) νSC(30)+ τONOS(14) νNC(10)+ βOSN(43) βNCC(19) βNCC(12)+ βNSC(15) βSCC(52)+ τONCS(16) βCNS(15)+ τCNSC(21) βCCN(17)+ βCCS(25)+ τSCCC(11) ƮτONCC(49) βτNSC(10)+ τONCC(42)


87 88 89 90

4232188

0.220.340.22

15.23

7.415.117.224.8

τHCCC(94) τCCNS(15)+�NSCC(56) τCNSC(50)+�NSCC(27) τCCNS(58)


Figure 8.4(a) FTIR spectrum of 4M4NPBS

Figure 8.4(b) FTRaman Spectrum of 4M4NPBS

4000 3500 3000 2500 2000 1500 1000 500

Wavenumber(cm-1)

Experimental

Tran

smitt

ance

(arb

.uni

ts)

B3LYP


201

stretches. C-H symmetric stretching is observed at 3288 cm-1 in FTIR and at 3075

cm-1 in FT-Raman. The C-H in plane bending vibrations usually occurs in the

region 1430-990 cm-1 and is very useful for characterization purposes [47]. As

stated in the earlier literature [47], in this work, the peaks at 1445, 1440 and 1024

occur due to the C-H in-plane-bending vibrations. The substitution patterns on the

ring can be judged from the out of plane bending vibrations of the ring C-H bond

in the region 900-675 cm-1 which are highly informative [48]. The modes

calculated at 822, 817, 791 and 790 cm-1 confirms the C-H out of plane bending

vibrations.

8.4.3 C-C Vibrations

The bands in the region 1430-1650 cm-1 are usually assigned to C-C

stretching modes [49-51]. As predicted in the earlier references, in this case, the

prominent peaks at 1598, 1492 and 1333 cm-1 are assigned to the ring C-C

stretching vibrations. The C-C-C in plane and out of plane bending vibrations are

calculated at 991, 986, 610, 550, 393 and 328 cm-1 and 693, 668, 488, 405 and 400

cm-1 respectively.

8.4.4 Methyl Group Vibrations

In general, the C-H stretching of methyl group occurs at lower frequencies

than those of aromatic ring (3100-3000 cm-1). The calculated values 2923-3010

cm-1 assigned to methyl C-H stretching modes in B3LYP/6-31G (d, p) method. The

vibrations of methyl group in this molecule are observed at 2922 and 2927 cm-1 in

FTIR and FT-Raman respectively. These assignments are within the characteristic

range as reported in earlier literatures [52-56]. The modes calculated at 1165, and


202

1024 cm-1 in B3LYP are assigned to C-H in-plane bending vibrations, which are in

good agreement with the value reported by Durig et al [57].

8.4.5 Heavy Atoms Fundamental Vibrations

The asymmetric and symmetric stretching modes of SO2 group appear in

the region 1360–1310 cm-1 and 1165–1135 cm-1 [58]. The observed bands at 1333,

1160 cm-1 in the FTIR spectrum, 1318, 1163 in the FT-Raman spectrum and 1264,

1102, 1094 and 1046 cm-1 theoretically are assigned as SO2 stretching modes. The

SO2 scissoring and wagging vibrations occur in the range 570 ± 60 cm-1 and

520 ± 40 cm-1 [58]. The corresponding bands are observed for the title compound

at 565 cm-1 and 585 cm-1 in the FT-IR spectrum, calculated as 550 and 515 cm-1

respectively.

The Raman bands at 1587 and 1525 cm−1 as weak intensities have been

assigned to NO2 asymmetric stretching vibrations. The IR and Raman bands

observed at 1348, and 1354 cm−1 have been assigned to NO2 symmetric stretching

vibrations. Aromatic nitro compounds have a band of weak-to-medium intensity in

the region 590–500 cm−1 [50] due to the in-plane deformation mode of the NO2

group. The NO2 in plane vibrations are observed at 813 in IR, 812 in FT-Raman

and 829 cm-1 in B3LYP. The NO2 out of plane deformation vibrations are expected

in the region 775–662 cm−1 [50]. The observed bands in IR at 760 cm−1 and in

Raman at 756 cm−1 as weak intensities have been assigned to NO2 out of plane

deformation.

Because of the mixing of several bands, the identification of C-N vibrations

is a very difficult task. In the present work, the band observed at 1256 cm-1 in FT-

Raman spectrum have been assigned to C-N stretching vibration. The mode 61


203

calculated at 1264 cm-1 with 6-31G(d,p) basis set is in good agreement with

experimental value. The PED of this mode is 20%. The PED of this mode suggests

that this is a mixed mode.

8.5 FTNMR SPECTRAL ANALYSIS

The FTNMR spectra are presented in Figure 8.6(a) and Figure 8.6(b)

respectively and the chemical shifts are tabulated with the assignments in

Table 8.4. As it is seen in Figure 8.6 (a), this compound shows thirteen different

carbon atoms, which is consistent with the structure on the basis of molecular

symmetry. 1H NMR spectrum Figure 8.6 (b) of the title compound is investigated,

it can be seen that total number of protons are in agreement with the integration

values presented in this spectrum.

Chemical shifts were reported in ppm relative to TMS for 1H NMR and 13C NMR spectrum provides information about the number of different types of

protons and also the nature of immediate environment of each of them. 13C NMR

spectrum also provides the structural information with regard to different carbon

atoms present in the molecules. In the 1H NMR spectrum, a singlet at 2.4 ppm

indicates the three protons of methyl group. The above said methyl group protons

are calculated in the range of 1.8 ppm - 2.21 ppm for B3LYP. The eleven aromatic

protons of nitrophenyl and tosyl group are appeared as multiplet in the range of

7.2-8.2 ppm and are calculated in the range of 7.72-8.41 ppm for B3LYP. The N1H

group of the nitrophenyl is responsible for the appearance of broad singlet at 4.36

ppm and calculated as 5.88 ppm for B3LYP. In general, highly shielded protons

appear downfield and vice versa. The protons associated with the carbons C5 and


Table 8.5 The chemical shift in 1H NMR and 13CNMR spectrum of 4M4NPBS crystal

Spectrum Experimental (CDCl3) signal at δ(PPM)

B3LYP Calculated Chemical shift at δ(PPM)

Group Identification

1H NMR 2.4(singlet)

2.21, 1.8, 1.8

3 protons of the Methyl carbon(C11)

8.2 8.29 8 7.79 7.78 7.77 7.37 7.2

8.41 8.29 8 7.98 7.98 7.98 7.78 7.72

Proton of (C6)29 Proton of (C2)8 Proton of (C11)24 Proton of (C13)9,7,10 Proton of (C5)26 Proton of (C3)28 Proton of (C10) 19 Proton of (C9)

4.36 5.88 N‐H Proton 13C NMR 20.05 10.97 C11 methyl group carbon 143.46 143.1 C 27(methyl group attached carbon) 136.67 130.64 C6(methyl group attached carbon) 134.40 127.83 C20 (N‐H attached carbon) 129.17 119.76 C23(SO2 attached carbon) 129.07 118.99 C21 126.91 118.05 C3 126.85 116, 115.89 C2Meta carbons of tolyl ring 121.62 115.7, 115.16 C4Ortho carbons of tolyl ring 121.58 115.01 C1 121.53 109.64 C5 76.77‐77.28 79.86 Carbon of the solvent CDCl3


Figure 5a H1 NMR spectrum of 4M4NPBS


Figure 5b C NMR spectrum of 4M4NPBS


204

C3 are appeared at higher chemical shift of 8.2 and 8.29 ppm experimentally and

8.41, 8.29 ppm theoretically due to the electronegative effect of nitro group. The

protons associated with C8 and C12 are appeared at high chemical shift of 8 and

7.79 ppm, calculated as 8 and 7.98 ppm due to the sulfonyl group. The protons

associated with C11 and C9 are appeared at upfield chemical shift of 7.78 and 7.77

ppm, calculated as 7.98 and 7.98 ppm because of shielding by the

hyperconjugative effect of methyl group. The protons associated with C6 and C2

carbons are appeared at 7.37 and 7.2 ppm in the proton NMR spectrum, calculated

as 7.78 and 7.72 ppm respectively.

In the 13C NMR spectrum, the methyl carbon of the tolyl group give signal

at 20.05 ppm, calculated as 10.97 ppm. The sixteen aromatic carbons of the

nitrophenyl and tolyl group are appeared as multiplet in the range of

121.53–143.46 ppm and are found to be in the range of 109.64–143.10 ppm for

B3LYP. The C1 carbon of the phenyl ring appears 143.46 ppm, due to

neighbouring N-H group, calculated as 143.1 ppm. The signal at 136.67 ppm is

assigned to the C10 carbon of the tosyl ring which is bonded with methyl group,

calculated as 130.64 ppm. The signal at 134.40 ppm is assigned to the C4 carbon

of the phenyl ring which is bonded with nitro group, calculated as 127.83 ppm.

The signal at 129.17 ppm is assigned to the C7 carbon of the tolyl ring which is

bonded with sulfonyl group, calculated as 119.76 ppm. The Meta carbons

(C9,C11) of the tosyl ring are responsible for the signal at 126.85 ppm, calculated

as 116 ppm and 115,89 ppm. The ortho carbons (C8, C12) of the tosyl ring are

responsible for the signal at 121.62 ppm, calculated as 115.7 ppm and 115.16 ppm.

The signals at 129.07 ppm, 126.91 ppm, 121.58 ppm, 121.53 ppm are assigned to

the (C3,C5,C2 and C6) carbons of the nitrophenyl ring. The above said carbons of

the nitrophenyl ring are calculated as, 118.99 ppm, 118.05 ppm, 115.01 ppm and


205

109.64 ppm for B3LYP. (See ortep diagram for numbering of atoms). A Signal at

76.77–77.28 ppm indicates the carbon atom of the CDCl3 (solvent), calculated as

79.86 ppm. As it is seen from the Table 4, calculated 1H and 13C chemical shifts

values of the title compound are generally agreement with the experimental 1H and

13C chemical shifts data.

In this study, GIAO 13C and 1H NMR chemical shifts of the molecules

were calculated and tabulated in Table 8. 6.

8.6 NBO ANALYSIS

NBO analysis provides a possible ‘natural Lewis structure’ picture of ø,

because all orbital details are mathematically chosen to include the highest possible

percentage of the electron density. A useful aspect of the NBO method is that it

gives information about interactions in both filled and virtual orbital spaces that

could enhance the analysis of intra- and intermolecular interactions.

The second order Fock matrix was carried out to evaluate the donor–

acceptor interactions in the NBO analysis. 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) associated with the delocalization i→j is estimated as

E(2) = ∆Eij = qi ⎟⎟⎠

⎞⎜⎜⎝

⎛

− )(),( 2

ij

jiFεε

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

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

provides an efficient method for studying intra and intermolecular bonding and


206

interaction among bonds, and also provides a convenient basis for investigating

charge transfer or conjugative interaction in molecular systems. The larger the E(2)

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 Rydgberg) 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 intra molecular, rehybridization 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

C-N) and σ* and π* of (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 electron density of conjugated

double as well as single bond of the aromatic ring (~1.9e) clearly demonstrates

strong delocalization inside the molecule. The strong intramolecular

hyperconjugation interaction of the σ (C –C) to the π*(C–C) bond in the ring leads

to stabilization of some part of the ring as evident from Table 8.5. For example, the

intra molecular hyper conjugative interaction of σ (C3–C4) distribute to σ * (C2–

C3) leading to stabilization of ~5.0 kJ/mol. This enhanced further conjugate with

anti-bonding orbital of π*(C1–C2) and (C5–C6), leads to strong delocalization of

22.24 and 14.52 kJ/mol respectively. The magnitude of charges transferred from

(LP(2)O32)→(C23-H28) shows weak intramolecular interaction which is shown in

the hydrogen bonding interactions of XRD result. The magnitude of charges


Table 8.6. 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)

C5‐C6 π 1.6183 C1‐C2 π * 0.2995 17.21 0.28 0.063

C3‐C4 π * 0.4029 27.27 0.26 0.076

C21‐C23 π 1.6501 C20‐C22 π * 0.3573 21.52 0.28 0.069

π C25‐C27 π * 0.3779 20.89 0.27 0.068

C3‐C4 π 1.6867 C1‐C2 π* 0.2995 22.24 0.30 0.073

C5‐C6 π* 0.3339 14.52 0.30 0.060

C20‐C22 π 1.654 C21‐C23 π* 0.3060 19.28 0.29 0.068

C25‐C27 π* 0.3779 21.59 0.28 0.070

C25‐C27 π 1.6711 C20‐C22 π* 0.3881 18.56 0.29 0.066

C21‐C23 π* 0.3069 20.31 0.31 0.070

S15‐O16 σ 1.9855 C2‐C3 σ* 0.0262 1.37 1.52 0.041 C22‐C25 σ 1.9721 N18‐C20 σ* 0.0305 4.37 1.03 0.060 LP(2)O16 σ 1.8166 S15‐N18 σ* 0.0254 12.6 0.44 0.068 LP(2)O16 σ 1.8166 C3‐S15 σ* 0.1779 0.83 0.73 0.023 C3‐C4 π* 1.6867 C1‐C2 π* 0.2995 172.35 0.02 0.078 C25‐C27 π* 1.6711 C21‐C23 π* 0.3060 203.15 0.01 0.081 N30‐O31 π* .58628 C25‐C27 π* 0.37794 10.94 0.08 0.037

a E(2) means energy of hyper conjugative interaction (stabilization energy). b Energy difference between donor and acceptor i and j NBO orbitals. c F(i,j) is the fork matrix element between i and j NBO orbitals.


207

transferred from (LP(2)O16)→(S15-N18) and (LP(1)N18)→(C20-C21) show that

stabilization energy of about ~12.6 KJ/Mol and ~ 6 KJ/Mol respectively. The

delocalization of electron π*(C3-C4) and π*(C25-C27) to π*(C1-C2) and π*(C21-

C23) with enormous stabilization energy of about ~ 172.35 and 203.15 KJ/Mol.

8.7 NONLINEAR OPTICAL EFFECTS

NLO is a forefront of current research because it provides the key functions

of frequency shifting, optical modulation, optical switching, optical logic, and

optical memory for the emerging technologies in areas such as

telecommunications, signal processing, and optical interconnections. The

hyperpolarizability values of 4M4NPBS calculated by the B3LYP/6-31G(d,p)

method is 4.60 x 10-31 cm5/esu and are listed in Table 8.6 (the β of urea is 6.06x10-

31 cm5/esu obtained by DFT (B3LYP)/6-31G(d,p) method). The first

hyperpolarizability of the title compound is 6.81 times that of urea. Conclusion

from the magnitude of the first hyperpolarizability, the 4M4NPBS compound may

be a potential applicant in the development of NLO materials.

8.8 MULLIKEN ATOMIC CHARGES

Atomic charges of the 4M4NPBS compound, computed by Mulliken

method at the B3LYP/6-31G(d,p) level of calculation, are illustrated in

Table 8.7. The magnitudes of the carbon atomic charges for the compounds were

found to be both positive and negative at the basis set. These magnitudes were

obtained to change between − 0.3836 and 0.2339 for 4M4NPBS. The maximum

atomic charge was obtained for C11 atom due to the effect of negatively charged

carbon atoms. The magnitude of N atoms were computed to be about −0.6455

(N18 and 0.2078(N30)). All the oxygen atomic charges were obtained to be

negative. Oxygen atoms of sulfonyl group have more negative charges (-0.526,


Table 8.7

The electric dipolemoment(D), Polarizability and first hyperpolarizability of 4M4NPBS

a.u esu(x10‐24) a.u (esux10‐33) αxx 255 1723 Βxxx 433.52 3745 αxy ‐7.38 49.86 Βxxy 83.91 724.81 αyy 171.87 1161.32 Βxyy 60.7 524.38 αxz ‐22.2 150 Βyyy 84.94 733.79 αyz ‐5.28 35.67 Βxxz ‐4.77 41.21 αzz 100.9 681.78 Βxyz ‐2.43 20.99αtotal 175.92 1188.69 Βyyz 3.86 33.34 µx ‐2.24 15.13 Βxzz ‐46.91 405.25 µy 1.11 Βyzz .103 .8898 µz 1.12 Βzzz 26.96 232.907 µ 2.95 Βtotal 478.86 4132.58


208

-0.523) than oxygen atoms of nitro group (-0.2939, -0.2932). Additionally, the

magnitudes of the hydrogen atomic charges were noted to be only positive values,

indicating the charge transfer from hydrogen to carbon atom. All the hydrogen

atoms in the molecules lost electrons.

8.9 MOLECULAR ELECTROSTATIC POTENTIAL

Molecular Electrostatic potential at the B3LYP/6-31G(d,p) optimized

geometry was calculated. The molecular electrostatic potential (MEP) is related to

the electronic density and a very useful descriptor for determining sites for

electrophilic attack and nucleophilic reactions as well as hydrogen–bonding

interactions. As it is seen in Figure 8.7, the red region is localized on the oxygen

atoms of nitro group and sulfonyl group has value of -0.0829 a.u. and the

maximum blue region localized on the N1–H1 bond has value of +0.0585 a.u,

indicating the possible sites for electrophilic attack and nucleophilic reaction

respectively. These sites give the information about the region, from where the

compound can have intermolecular interactions. Hence, the molecular electrostatic

potential map confirms the existence of intermolecular N–H-O interactions.

8.10 ELECTRONIC ABSORPTION SPECTRUM

General types of electronic transitions in organic compounds are π–π* and

n–π*. In order to understand the electronic transitions of the 4M4NPBS compound,

theoretical calculations on electronic absorption spectra were performed in gas

phase by TD-B3LYP/6-31G(d,p) method. The absorption peak obtained at 225 nm

is attributed to the π–π* type transition in benzene ring and oscillation effect. The

weak absorption peak at 309 nm denotes n→π* type transition in nitro group.


Figure 8.6 The Mulliken charge distribution of 4M4NPBS


Figure 8.7 Molecular Electrostatic Potential of 4M4NPBS


Figure 8.8 UV‐Vis absorption spectrum of 4M4NPBS


209

8.11 HOMO-LUMO ANALYSIS

Highest occupied molecular orbital (HOMO) and lowest unoccupied

molecular orbital (LUMO) are very important parameters for quantum chemistry.

The way the molecule interacts with other species will be determined by them.

Hence, they are called the frontier orbitals. HOMO, which can be thought the

outermost orbital containing electrons, tends to give these electrons such as an

electron donor. On the other hand; LUMO can be thought the innermost orbital

containing free places to accept electrons. Due to the interaction between HOMO

and LUMO orbital of a structure, transition state transition of π-π* type is

observed with regard to the molecular orbital theory. Therefore, while the energy

of the HOMO is directly related to the ionization potential, LUMO energy is

directly related to the electron affinity. According to B3LYP/6-31G(d,p) level of

theory, the energy band gap between HOMO and LUMO) was found to be about

3.51eV. The HOMO and LUMO energies calculated present that the charge

transfer occurs within the molecules. Moreover it is visible from Figure. 8.9, the

highest occupied molecular orbital (HOMO) is localized on the nitrophenyl and

NH-SO2 group. LUMO is delocalised only over the nitrophenyl ring. HOMO-

LUMO transition is taking place from NH-SO2 moiety to nitrophenyl ring.

By using HOMO and LUMO energy values, the global chemical reactivity

descriptors of molecules such as hardness, chemical potential, softness,

electronegativity and electrophilicity index as well as local reactivity have been

calculated and their values are shown in the Table 8.8.

8.12 THERMAL ANALYSIS

4M4NPBS compound is found to be stable upto the temperature of about to

295°c. From 295°c, the first stage of decomposition starts. It goes upto nearly

380°c with a total mass loss of 35%. The second stage decomposition begins at the


Figure 8.9 HOMO‐LUMO surfaces of 4M4NPBS


Figure 8.10 TGA and DTA of 4M4NPBS


210

temperature of 570°c. The decomposition becomes complete at about 670°c with

the whole mass of the compound getting decompose, leave behind less than 10%

of charred material.

8.13 CONCLUSION

In this chapter, 4M4NPBS was studied using experimental techniques

(FT-IR, FT-Raman, NMR and UV) and tools derived from the density functional

theory. The vibrational FT-IR and FT-Raman spectra of 4M4NPBS was recorded

and detailed description of vibrational modes were assigned with the aid of

potential energy distribution analysis. The electronic properties were also

calculated and compared with experimental electronic spectrum. The comparisons

of the predicted bands are generally in good agreement with experimental results.

Furthermore, total dipole moment, linear polarizability, first hyperpolarizability of

the 4M4NPBS molecule were calculated and the results were discussed. These

results indicate that the studied compound is a good candidate for nonlinear optical

materials.


211

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