Quantum mechanical study of the structure and spectroscopic (FT-IR, FT-Raman), first-order hyperpolarizability, NBO and HOMO–LUMO analysis of S-S-2 methylamino-1-phenyl propan-1-ol

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 386–398

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Quantum mechanical study of the structure and spectroscopic (FT-IR, FT-Raman), first-order hyperpolarizability, NBO and HOMO–LUMO analysis of S-S-2 methylamino-1-phenyl propan-1-ol G. Ramachandran b, S. Muthu a,⇑, S. Renuga c a b c

Department of Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602 105, Tamil Nadu, India Research Scholar, Bharathiyar University, Coimbatore, Tamil Nadu, India Department of Physics, Indira Institute of Engineering and Technology, Thiruvallur, Tamil Nadu, India

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

" A detailed interpretation of Infrared

S-S-2 methylamino-1-phenylpropan-1-ol (SSMPL) is used in the treatment of Nasal congestion. The equilibrium geometry harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated by density functional (B3LYP) method with 6-31G(d,p), 6-311++G(d,p) basis sets, using Gaussian 03W program. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule.

and Raman spectra of SSMPL were reported. " Molecular structural parameters of the geometry have been computed by DFT method with 6-31G(d,p), 6-311++G(d,p) basis sets. " HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule.

a r t i c l e

i n f o

Article history: Received 30 October 2012 Received in revised form 27 December 2012 Accepted 10 January 2013 Available online 31 January 2013 Keywords: FTIR FT-Raman First order hyperpolarizability NBO TED

a b s t r a c t The experimental and theoretical vibrational spectra of S-S-2 methylamino-1-phenyl propan-1-ol (SSMPL). Fourier transform infrared (FTIR) and FT Raman spectra of SSMPL in the solid phase were recorded and analyzed. The molecular geometry, vibrational frequencies, infrared intensities, Raman activities and atomic charges were calculated using density functional theory calculation (B3LYP) with standard 6-31G(d,p) and high level 6-311++G(d,p) basis sets. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT Raman data. The thermodynamic functions of the title compound were also performed by B3LYP with two basis sets 6-31G(d,p) and 6-311++G(d,p). Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Using the method B3LYP, the dipole moment (l), polarizability (a) and the hyperpolarizability (b) values of the investigated molecule has been computed. Total energy distribution (TED) was used for the assignment of Unambiguous vibrational fundamental modes. Finally, Simulated FTIR and FT Raman spectra of SSMPL showed good agreement with the observed spectra. Ó 2013 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 9443690138; fax: +91 4427162462. E-mail address: [email protected] (S. Muthu). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.01.026

G. Ramachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 386–398

Introduction SSMPL is a sympathomimetic drug, which is used in the treatment of Nasal congestion. It is a natural alkaloid and is produced for commercial use derived from Yeast fermentation of dextrose in the presence of benzaldehyde. Its principal mechanism of action relies on its indirect action on the adrenergic receptor system. The vasoconstriction that compound produces is believed to be principally a a-adrenergic receptor response [1]. A wide variety of pharmacological properties has been associated with benzaldehyde derivatives. It may be used as anti-tussive drug [2] and SSMPL is also used as first-line therapy of priapism. Erection is largely a parasympathetic response, so the sympathetic action of SSMPL serves as to relief to this condition. Treatment for urinary incontinence is an unlabeled use for these medications [3]. Loratadine plus SSMPL, significantly improved nasal and asthma symptoms, pulmonary function, and quality of life in patients with seasonal allergic rhinitis and concomitant mild asthma [4] and it is an adjunct to other agents in the optimum treatment of allergic rhinitis, croup, sinusitis, otitis media, and tracheo bronchitis [5]. It may be quantities in blood, urine to monitor any possible performanceenhancing use by athletes, confirm a diagnosis of poisoning or assist in a medicolegal death investigation [6]. A new material of pyridine with an infinite pseudo-layered structure and manifested NLO application [7]. SSMPL related organo gold compound was synthesized and analyzed by laser-Raman spectra [8]. In the light of these interesting biological activities, it was our interest to shower our knowledge to report the results of Density functional theory calculations of SSMPL. The FT IR and Raman spectra of this compound have been simulated with the use of the standard 6-31G(d,p) and 6-311++G(d,p) basis set. Experimental data on molecular vibrations were obtained by FTIR and FT-Raman measurements. We have investigated the complete geometrical parameters, modes of vibrations, dipole moment, polarizability, Hyperpolarizability rotational constants, atomic charges and other thermodynamic parameters of the title molecule using B3LYP calculations with 6-31G(d,p) and 6-311++G(d,p)basis sets. Specific scale factors were employed in the predicted frequencies for the accuracy. The change in electron density (ED) in the r anti-bonding orbital and stabilization energies E(2) have been calculated by natural bond (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions. In addition, HOMO, LUMO analyses have been used to elucidate the information regarding charge transfer within the molecule. Methodology Experimental High grade pure sample of SSMPL was purchased from sigma chemical company USA and used as such FTIR spectrum has been recorded in the region 4000–450 cm1 in evacuation mode using KBR pellet technique (solid phase) with 4.0 cm1 resolution on a BRUKER RFS 100/S at BMT WING, SCTIMST, Trivandrum, India. The FT Raman spectrum has been recorded in the region 4000– 100 cm1 in pure mode using Nd-Yag laser of 200 mw, the spectra was recorded using BRUKER IFS 66 V spectrophotometer with sophisticated instrumentation analysis facility, IIT, Chennai, India. The observed experimental and stimulated FT-IR and FT-Raman spectra are shown in Figs. 1 and 2 respectively. Computational The entire calculations were performed at density functional (DFT) levels on a Pentium IV personal computer using Gaussian

387

03 [9] program package invoking gradient geometry optimization [10]. The harmonic vibrational frequencies were calculated at the same level of theory for the optimized structures and obtained frequencies were scaled by 0.913 and 0.961, 0.958, 0.983 [11]. Initial geometry generated from standard geometrical parameters was minimized without any constraint in the potential energy surface at DFT level, adopting the standard 6-31G(d,p) basis set. This geometry was then re optimized again at DFT levels, using the higher basis set. The optimized structural parameters were used in the vibrational frequency calculation at DFT levels to characterize all stationary points as minima. We have used B3LYP approach for the computation of molecular structure vibrational frequencies and energies of optimized structures in the present work using GAUSSVIEW program with symmetry considerations along with available related molecules, the vibrational frequency assignments were made with a high degree of accuracy. The natural bonding orbital (NBO) calculations [12] were performed using NBO 3.1 program as implemented in the Gaussian 03W package at the above said level in order to understand various second order interactions between the filled orbital of one subsystem and vacant orbital of another subsystem, which is a measure of the intermolecular and intra molecular delocalization or hyper conjugation. Prediction of Raman intensities and hyperpolarizability The Raman activities (Si) calculated with the GAUSSIAN 03W program were subsequently converted to relative Raman intensities (Ii) using the following relationship derived from the theory of Raman scattering [13–15].

Ii ¼

f ðt0  ti Þ4 Si ti ½1  expðhcti=kb TÞ

where t0 is the exciting frequency in cm1 ti is the vibrating wave number of the ith normal mode h, c and kb are the fundamental constants and f is a normalization factor for all peak intensities. The first hyperpolarizabilities (b0) of this novel molecular system, and related properties (b, a0 and a) of SSMPL were calculated using B3LYP with 6-31G(d,p) and 6-311++G(d,p) basis sets, based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. Polarizabilities and hyperpolarizabilities characterize the response of a system in an applied electric field [16]. They determine not only the strength of molecular interactions (longrange inter induction, dispersion force, etc.) as well as the cross sections of different scattering and collision process but also the nonlinear optical properties (NLO) of the system [17,18]. First hyperpolarizability is a third rank tensor that can be described by 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Klein man symmetry [19]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3  3  3 matrices is a tetrahedral. The components of b are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes,

1 1 E ¼ E0  la F a  aab F a F b  babc F a F b F c þ . . . 2 6 where E0 is the energy of the unperturbed molecules, Fa the field at the origin la and aab, babc are the components of dipole moments, polarizability and the first hyperpolarizabilities, respectively. The total static dipole moments l, the mean polarizabilities a0, the anisotropy of the polarizabilities a and the mean first hyper-polarizabilities b, using the x, y and z components are defined as: [17,18].

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Fig. 1. FTIR spectra of SSMPL: (A) experimental, (B) DFT/6-311++G(d,p), and (C) DFT/6-31G(d,p).

Fig. 2. FT-Raman spectra of SSMPL: (A) experimental, (B) DFT/6-311++G(d,p), and (C) DFT/6-31G(d,p).

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The total static dipole moment is

l ¼ ðl2x þ l2y þ l

2 1=2 zÞ

The isotropic polarizability is

a0 ¼

ðaxx þ ayy þ azz Þ 3

The polarizability anisotropy invariant is

a ¼ 21=2 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xx 1=2 And the average hyperpolarizability is

b0 ¼ ðb2x þ b2y þ b2z Þ1=2

polarizabilities and first hyperpolarizabilities of SSMPL are, 464.5383 a.u, 517.4847 a.u and 1.5924  10–30 esu, 2.0918  10–30 esu by B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) levels, which are comparable with the reported values of similar derivatives [20,21]. The magnitude of the molecular hyperpolarizability b, is one of key factors in a NLO (non-linear optical) system. Total dipole moment of title molecule is approximately to those of urea and first order hyperpolarizability of title molecule is greater than those of urea [22]. Hence we conclude that the title compound is an attractive object for future studies of nonlinear optical properties.

Results and discussion

And Molecular geometry

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bz ¼ bzzz þ bxxz þ byyz The total static dipole moment, polarizabilities and first hyperpolarizabilities of SSMPL were calculated. Table 1 lists the values of the electric dipole moment (Debye) and dipole moment components, polarizabilities and hyperpolarizabilities of the SSMPL. In addition to the isotropic polarizabilities and polarizabilities anisotropy invariant were also calculated. The calculated value of dipole moment was found to be 1.0278 at B3LYP/6-311++G(d,p) level. The

The molecular structure of the SSMPL belongs to C1 point group symmetry. The optimized molecular structure of title molecule is obtained from GAUSSIAN 03W and GAUSSVIEW programs as shown in Fig. 3 The comparative optimized geometrical parameters of SSMPL calculated by B3LYP levels with the 6-311++G(d,p) and 6-31G(d,p) basis sets are listed in Table 2. From the theoretical values, it is found that most of the optimized benzene ring C–C bond lengths and C–H bond lengths are exactly coincides with the experimental values at B3LYP/6-311++G (d,p) level, and slightly larger values at B3LYP/6-31G(d,p) level, due to this the

Table 1 The dipole moments l, polarizability a0, the anisotropic polarizability a, the and the first hyperpolarizability (10–33 esu) of SSMPL, using B3LYP method with 6-31G(d,p) and 6-311++G(d,p) basis sets. Parameters

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

Parameter

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

lx ly lz l axx axy ayy axz ayz azz a0 a

0.5062 0.7950 0.4101 1.0278 147.9887 7.7514 122.2152 6.3211 1.0260 107.7662 125.9900 517.4847

0.5150 0.7465 0.4810 1.0245 132.0249 7.1675 106.1854 6.0310 1.5375 85.1185 107.7764 464.5323

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz btot (esu)

59.0813 61.5795 6.1388 91.0380 91.6118 21.9002 29.8503 61.0275 58.5242 8.2468 2.0918  1030

139.5053 68.1807 17.3308 58.2165 80.0023 5.9654 17.2604 11.2013 15.0103 0.3192 1.5924  1030

Fig. 3. Numbering system adopted in this study (SSMPL).

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Table 2 Geometrical parameters optimized in SSMPL by B3LYP with 6-31G(d,p) and 6-311++G(d,p) basis sets. 0

Bond length (Å A) C1–C2 C1–O4 C1–C5 C1–H13 C2–C3 C2–N11 C2–H14 C3–H15 C3–H16 C3–H17 O4–H18 C5–C6 C5–C10 C6–C7 C6–C19 C7–C8 C7–H20 C8–C9 C8–H21 C9–C10 C9–H22 C10–H23 N11–C12 N11–H24 C12–H25 C12–H26 C12–H27 Bond angle (°) O4–C1–C2 H13–C1–C5 H13–C1–O4 C5–C1–O4 C3–C2–C1 N11–C2–C3 H14–C2–C1 H14–C2–C3 H15–C3–C2 H16–C3–C2 H17–C3–C2 H16–C3–H15 H17–C3–H15 H17–C3–H16 H18–O4–C1 C1–C5–C6 C1–C5–C10 C10–C5–C6 C7–C5–C6 H19–C6–C7 H19–C6–C5 C8–C7–C6 H20–C7–C6 H20–C7–C8 C9–C8–C7 H21–C8–C7 H21–C8–C9 C10–C9–C8 H22–C9–C8 C5–C10–C9 H23–C10–C5 H23–C10–C9 C2–N11–C12 H24–N11–C12 H25–C12–N11 H26–C12–N11 H27–C12–N11 H26–C12–H25 H27–C12–H25 a

B3LYP/6311++G(d,p)

B3LYP/631G(d,p)

Experimentala

1.523 1.402 1.497 1.113 1.523 1.438 1.113 1.113 1.113 1.113 0.942 1.337 1.337 1.337 1.100 1.337 1.100 1.337 1.100 1.337 1.101 1.101 1.438 1.020 1.113 1.113 1.113

1.547 1.431 1.517 1.102 1.540 1.460 1.099 1.094 1.096 1.093 0.966 1.401 1.400 1.394 1.083 1.397 1.086 1.394 1.085 1.394 1.085 1.084 1.461 1.018 1.093 1.094 1.104

1.523 1.402 1.497 1.113 1.523 1.438 1.113 1.113 1.113 1.113 0.942 1.337 1.337 1.337 1.100 1.337 1.100 1.337 1.100 1.337 1.100 1.100 1.438 1.020 1.113 1.113 1.113

109.499 109.520 109.461 109.442 109.497 109.441 109.462 109.458 109.499 109.442 109.462 109.440 109.463 109.518 119.999 119.999 120.001 119.998 119.999 119.671 119.999 119.999 120.001 119.999 119.999 119.999 120.002 120.002 120.001 120.002 120.001 119.997 109.441 109.438 109.496 109.445 109.461 109.438 109.465

105.515 107.745 109.483 112.429 112.419 111.876 104.720 107.634 111.256 109.500 110.901 107.648 108.544 108.907 107.520 120.940 120.409 118.650 120.720 120.089 119.190 120.189 119.629 120.117 119.502 120.274 120.223 120.259 119.699 120.677 119.339 119.975 114.888 107.790 110.389 108.932 114.204 107.294 107.702

109.500 109.520 109.461 109.441 109.500 109.441 109.461 109.461 109.500 109.441 109.461 109.441 109.461 109.520 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 120.000 109.500 109.441 109.500 109.441 109.461 109.441 109.461

Taken from Ref. [23].

theoretical calculations belong to isolated molecules in gaseous phase and the experimental results belong to molecules in solid state. Comparing bond angles and bond lengths of B3LYP with

two basis sets, as a whole the formers are bigger than later and the B3LYP calculated values correlates well compared with the experimental data. Further the result of our calculations showed that (C5–C10) and (C6–C7) bonds shows typical double-bond characteristics whereas (C2–N11), (C1–O4) bonds shows single bond characteristics. The very high bond length of strong bond which is found to be C2–C3 and smaller value of weak bond O4–H18 All other bond lengths fall within the expected ranges The comparative graphs of bond lengths, bond angles of title molecule are presented in Figs. 4 and 5 respectively. From the data shown in Table 2, it is seen that the B3LYP levels of theory in a general priority for reproducing the experimental bond lengths and bond angles [23] is not present DFT levels. All calculated geometrical parameters were obtained at the DFT levels of theory are in good agreement with the experimental structural parameters. The density functional calculation gives the angles O4–C1–C2, H13–C1–O4, C5–C1–O4, C5–C1–C2 are gradually increases and decreases the angles C3–C2–C1 to H18–O4–C1 at B3LYP/631G(d,p) level and all bond angle values are well coincides with experimental values at B3LYP/6-311++G(d,p) level. The electron donating substituent’s on the benzene ring, the symmetry of the ring is distorted, yielding ring angles smaller than 120° at the point of substitution and slightly larger than 120° at the ortho and Meta positions [24]. Due to the hyper conjugative effect of methyl group, it is observed that in SSMPL molecule the bond angle at the point of substitution C3–C2–C 1 is 109.497° while the bond angles in at ortho to the substituted carbon C5–C10–C9 position is found to be 120.002°. The variation in bond angle depends on the electro negativity of the central atom, the presence of lone pair of electrons and the conjugation of the double bonds. If the electro negativity of the central atom decreases, the bond angle decreases. Further the results of our calculations, the experimental and calculated geometric parameters agree well with remaining geometrical parameters. The small deviations observed are probably due to the intermolecular interactions in the crystalline state of the molecule. Vibrational analysis The vibrational spectrum is mainly determined by the modes of the free molecule observed at higher wave numbers, together with the lattice (translational and vibrational) modes in the low Wave number region. In our present study, we have performed a frequency calculation analysis to obtain the spectroscopic signature of SSMPL. The SSMPL molecule consists of 27 atoms therefore they have 75 vibrational normal modes. All the frequencies are assigned in terms of fundamental, overtone and combination bands. Assignments have been made on the basis of Total energy distribution (TED). The measured (FTIR and FT-Raman) wave numbers and assigned wave numbers of the some selected intense vibrational modes calculated at B3LYP level with two basis sets 6-31G(d,p), 6-311++G(d,p) along with their TED are given in Table 3. This reveals good correspondence between theory and experiment in main spectral features. The experimental and theoretical FTIR and FT-Raman spectra are shown in Figs. 1 and 2. The wave numbers calculated at B3LYP level with inclusion of IR and Raman spectra contain a number of bands at specific wave numbers. On the whole, the predicted vibrational wave numbers are in good agreement with the experimental results. C–H vibrations The hetro aromatic structure shows the presence of C–H stretching vibrations in the region 3100–3000 cm1. This is the characteristic region for the ready identification of C–H stretching vibrations [25]. These vibrations are found to be affected due to the nature and position of the substituent’s. Accordingly, in the present

G. Ramachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 386–398

391

Fig. 4. Bond length differences between theoretical B3LYP approaches of SSMPL.

Fig. 5. Bond angle differences between theoretical B3LYP approaches of SSMPL.

study, the IR bands are observed in the range 3100–3015 cm1 and one weak band observed at 3043 cm1 in Raman spectrum. The bands are deviated trivially from the expected range, this is clearly due to the influence of NH stretching vibrations, Which is found to be very-dominating in this molecule. Theoretically computed C–H vibrations by B3LYP method of scaled values approximately coincides with experimental values. As indicated by the TED, these modes (mode nos. 3–15) involve more than 90% of contribution, suggesting that they are pure stretching modes. The C–H in plane bending vibrations normally occurred as a number of strong to weak intensity sharp bands in the region 1300–1000 cm1 [26,27] and are very useful for characterization

purposes. The bands identified at 1512, 1490, 1470 cm1 in IR and bending vibrations identified at 1510, 1500, 1477, 1462, 1453 cm1 in Raman are assigned for C–H in plane bending. Methyl group vibrations The title molecule SSMPL under consideration possesses one CH3 unit which lies in the terminal group of molecule. For the assignments of CH3 group frequencies, nine fundamentals can be associated to each CH3 group [28]. The C–H stretching in CH3 occurs at lower frequencies than those of aromatic ring (3100– 3000 cm1). Moreover, the asymmetric stretch is usually at higher wave number than the symmetric stretch. Methyl group vibrations

Mode no.

Calculated (cm1)

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

FTIR

Raman

B3LYP/6-311++G(d,p)a

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

IIRb

IRamanc

IIRb

IRamanc

3581(w) 3424(w) 3100(ms) 3080(w) 3050(w) 3025(s) 3015(w) 2977(vw) 2953(ms) 2945(ms) 2918(vw) – 2832(w) 2816(vw) – – 1604(w) 1512(w) – 1490(s) – 1470(s) 1465(vs) 1455(vs) 1437(vs) – 1392(vw) 1373(vs) 1353(w) 1340(s) 1306(w) 1248(vw) 1202(vw) – – 1172(s) 1167(s) 1115(ms) 1093(w) 1083(vw) 1072(ms) – 1046(ms) 1021(vw) – 1010(w) 996(s) 989(w) 945(vw) 916(s) 876(vs) 822(vw) 798(vw) 772(s)

– 3421(s) – – 3043(w) – – 2987(s) 2955(s) 2947(s) – 2893(s) – – 2810(vw) 1645(w) – 1510(w) 1500(w) – 1477(w) – 1462(s) 1453(s) – 1400(w) 1390(vs) – – – 1302(w) 1247(ms) 1201(ms) 1187(s) 1176(s) – – 1105(s) 1092(vw) 1085(w) – 1051(s) – 1020(s) 1017(w) 1013(vw) 994(s) 986(w) 950(w) 919(s) 875(ms) 820(w) – 780(s)

3734 3461 3155 3129 3117 3106 3093 3060 3041 3038 2992 2976 2968 2909 2892 1590 1571 1471 1467 1456 1447 1439 1432 1426 1407 1352 1349 1334 1308 1302 1289 1263 1220 1172 1153 1137 1134 1123 1112 1069 1060 1034 1011 1004 973 952 948 927 899 882 831 821 804 740

3675 3406 3105 3080 3068 3057 3044 3012 2993 2990 2945 2929 2921 2863 2846 1598 1579 1479 1475 1463 1454 1446 1439 1433 1414 1359 1356 1341 1315 1309 1296 1269 1226 1178 1159 1143 1140 1129 1118 1074 1065 1039 1016 1009 978 957 953 932 904 887 835 825 808 744

27 3 7 43 45 0 14 36 53 47 66 45 30 75 168 0 0 9 22 12 0 4 20 35 9 13 39 1 17 3 1 20 49 9 4 36 20 69 29 32 16 10 3 32 0 0 63 0 1 1 46 0 4 76

145 69 120 318 118 127 63 75 98 110 106 203 50 77 158 43 13 1 29 21 9 36 0 8 18 4 84 56 21 1 6 4 5 26 10 16 12 9 14 5 7 21 46 6 39 0 6 0 14 2 6 5 9 6

19 2 5 30 31 0 10 25 37 33 46 31 21 52 117 0 0 6 15 8 0 3 14 24 6 9 27 1 12 2 1 14 34 6 3 25 14 48 20 22 11 7 2 22 0 0 44 0 1 1 32 0 3 53

140 67 116 323 114 123 61 72 95 106 102 196 48 74 153 42 13 1 27 19 8 33 0 7 17 4 24 16 6 1 6 4 5 25 10 7 5 4 6 2 3 9 20 6 39 0 6 0 14 2 6 5 9 6

Vibrational assignments with TED (%)

(O–H)c(100) (N–H)c(100) (C–H)ring c(94) (C–H) ring c(90) (C–H)ring c(90) (C–H)ring c(94) (C–H)ring c(95) (C–H)ring c(94) (C–H)c(98) (C–H)c(93) (C–H)c(92) (C–H)c(90) (C–H)c(91) (C–H)c(93) (C–H)c(91) (C–C)c(48) (C–C)c(44) (H–C–H)b(39) (H–C–H)b(43) (H–C–H)b(39) (H–C–H)b(13) (H–C–H)b(47) (C–H–H–H)q(47) (C–H–H–H)q(43) (H–C–O)b(18) (H–O–C)b(17) (C–H–H–H)q(17) (H–C–C)b(37) (H–C–C)b(39) (C–C)b(47) (H–C–N–C)s(18) (H–O–C)b(18) (H–C–C)b(17) (H–C–C)b(37) (H–C–C)b(37) (H–C–C)b(37) (H–C–N–C)s(18) (O–C)c(17) (O–C)c(15) (H–C–C–C)s(22) (O–C)c(25) (O–C)c(25) (O–C)c(17) (C–C)c(21) (C–C–C)b(30) (C–C)c(18) (H–C–C–C)s(18) (H–C–C–C)s(19) (H–C–C–C)s(22) (H–C–C–C)s(31) (N–C)c(23) (C–C)c(18) (C–C)c(18) (H–C–C–C)s(18)

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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 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Experimental (cm1)

392

Table 3 Vibrational assignments of fundamental modes of SSMPL along with calculated IR, Raman intensities and normal mode descriptions (characterized by TED) based on quantum mechanical force field calculations using B3LYP.

748(s) 702(s) 671(ms) 631(s) 571(s) 511(vw) 455(s) – – – – – – – – – – – – – –

– 705(s) – 630(w) 570(s) 502(ms) 453(ms) 416(w) 400(w) 361(w) 335(w) 320(vw) 286(w) 250(s) 235(w) 211(ms) 180(w) 120(vw)

708 682 668 608 598 525 434 400 376 324 292 290 255 231 217 209 183 122 86 64 33

712 686 671 611 601 528 436 402 378 326 294 291 256 232 218 210 184 123 86 64 33

95 53 20 6 16 10 0 0 9 14 99 76 6 4 0 3 0 1 0 1 0

8 1 1 5 4 0 1 0 4 2 3 0 2 0 0 1 1 0 3 4 10

66 37 14 4 11 7 0 0 6 10 69 53 4 3 0 2 0 1 0 1 0

8 1 1 5 4 0 1 0 4 2 3 0 2 0 0 1 1 0 3 4 10

(H–C–C–C)s(17) (C–C–C–C)r(13) (C–C–C)b(23) (C–C–C)b(37) (C–C–N)b(17) (N–C)c(18) (C–C–C–C)s18) (C–C–N)b(16) (H–O–C–C)s(11) (H–O–C–C)s(52) (O–C–C)b(19) (C–N–C)b(12) (H–C–N–C)s(14) (H–C–N–C)s(14) (H–C–C–C)s(14) (H–C–C–C)s(13) (H–C–N–C)s(13) (C–N–C–C)s(36) (N–C–C–C)s(53) (C–N–C–C)s(33) (C–C–C–C)s(64)

Abbreviations: s – strong; vs – very strong; ms – medium strong; w – weak; vw – very weak; c – stretching; b – in plane bending; r – out of plane bending; s – torsion; q – sym/asym deformation. a Scaling factor: 0.961 for B3LYP/6-31G(d,p) and 0.958,0.983 for B3LYP/6-311++G(d,p). b Relative absorption intensities normalized with highest peak absorption equal to 100. c Relative Raman intensities normalized to 100.

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55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75

393

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Table 4 Second order perturbation theory analysis of Fock matrix in NBO basis. Donor (i)

a b c

Type

ED (e)

C1–C2

r

1.9748

C2–H14

r

1.9792

C5–C6

r

1.9655

C5–C10

r

1.9694

C5–C10

p

1.6687

C6–C7

r

1.9746

C6–C7

p

1.6665

O4

LP2

1.9674

N11

LP1

1.9319

Acceptor (j) C3–H15 O4–H18 N11–C12 C3–H17 C1–C2 C2–H11 C1–C5 C5–C10 C6–C7 C7–H20 C10–H23 C5–C6 C6–H19 C9–C10 C9–H22 C1–O4 C6–C7 C8–C9 C7–C8 C8–H21 C5–C10 N11–H24 C1–C5 C1–H13 C2–C3 C2–H14 C12–H25 C12–H27

a

Type

ED (e)

E(2)



0.0059 0.0056 0.0044 0.0056 0.0350 0.0173 0.0036 0.0262 0.0184 0.0137 0.0150 0.0277 0.0149 0.0179 0.0137 0.0195 0.3132 0.3187 0.0185 0.0138 0.0262 0.0318 0.0336 0.0227 0.0190 0.0238 0.0159 0.0137

2.03 3.32 1.70 3.33 4.22 4.76 3.92 7.61 5.70 3.37 3.44 7.84 3.47 5.66 3.43 5.25 38.91 44.39 5.20 3.58 44.54 4.75 8.16 7.90 6.15 3.75 6.83 3.17

r r r r r r r r r r r r r r r r p p r r p r r r r r r r

(kJ/mol)

E(j)–E(i)b (a.u.)

F(i, j)c (a.u.)

1.52 1.63 1.48 1.37 1.30 1.32 1.67 1.93 1.93 1.70 1.69 1.91 1.70 1.92 1.69 0.93 0.54 0.54 1.92 1.69 0.53 1.10 1.19 1.18 1.09 1.13 1.13 1.12

0.050 0.066 0.045 0.061 0.066 0.071 0.072 0.108 0.094 0.068 0.068 0.109 0.069 0.093 0.068 0.068 0.130 0.138 0.089 0.070 0.137 0.070 0.088 0.087 0.074 0.059 0.080 0.054

E(2) means energy of hyper conjugative interaction (stabilization energy). Energy difference between donor and acceptor i and j NBO orbitals. F(i, j) is the Fock matrix element between i and j NBO orbital’s.

Fig. 6. Molecular electrostatic potential map calculated at B3LYP/6-31G(d,p) level.

are generally referred to as electron-donating substituent in the aromatic rings system, the antisymmetric C–H stretching mode of CH3 is expected around 2980 cm1 and CH3 symmetric stretching is expected at 2870 cm1 [29,30]. The antisymmetric C–H stretching mode of CH3 identified at 2987 cm1 in Raman spectrum and the bands are identified at 2810, 2873 cm1 in IR spectrum for CH3 symmetric stretching. The calculated wave numbers by B3LYP method are approximately coincide with the experimental results. For methyl substituted benzene derivatives, the antisymmetric and symmetric deformation vibrations of methyl group normally appear in the region 1465–1440 cm1 and 1390–1370 cm1,

respectively [31–33]. In this case, the bands are identified at 1465, 1455, 1392 in IR and similar vibrations are identified at 1462, 1453, 1390 in Raman spectrum. O–H vibrations The O–H group vibrations are likely to be the most sensitive to the environment; hence they show pronounced shifts in the spectra of the hydrogen bonded species. The O–H stretching vibration is normally observed around 3300 cm1 [34]. The assignment of these bands to O–H stretching vibrations is straightforward. The O–H in-plane and out-of-plane bending vibrations are usually observed in the regions 1350–1200 cm1 and 720–590 cm1 [35,36]

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and this may be due to the presence of intermolecular hydrogen bonding.

Fig. 7. The atomic orbital compositions of the frontier molecular orbital for SSMPL.

Table 5 HOMO–LUMO energy value of SSMPL calculated by B3LYP methods with 6-31G(d,p) and 6-311++G(d,p) basis sets. Parameter

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

HOMO energy LUMO energy Energy difference

0.3560 ev 0.1954 ev 0.49547 (a.u)

0.3404 ev 0.1825 ev 0.48896 (a.u)

Table 6 Mulliken population analysis of SSMPL performed at B3LYP methods with 6-31G (d, p) and 6-311++G(d,p) basis sets. Atom with numbering

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

C1 C2 C3 O4 C5 C6 C7 C8 C9 C10 N11 C12 H13 H14 H15 H16 H17 H18 H19 H20 H21 H22 H23 H24 H25 H26 H27

0.01511 0.89912 0.29703 0.21394 0.28216 0.10161 0.31073 0.46057 0.31609 0.05346 0.19862 0.34093 0.19756 0.09695 0.12870 0.13948 0.16477 0.26296 0.18217 0.18143 0.14825 0.17772 0.14126 0.30352 0.15159 0.10694 0.11426

0.16428 0.02867 0.2458 0.5555 0.02748 0.1340 0.0638 0.0812 0.0821 0.1134 0.4968 0.1645 0.06681 0.08035 0.08095 0.09000 0.10655 0.29996 0.11468 0.08644 0.08138 0.08108 0.07799 0.27539 0.10236 0.08702 0.08586

respectively. The strength and broadening wave numbers of these bands suggest that intra molecular hydrogen bonding occurs in different environments of boronic acids [37]. In accordance with the above conclusion, the O–H stretching vibration occurs at 3424 cm1 in the FTIR spectrum. In this case, a strong bond in FTIR spectrum at 3581 cm1 is assigned to O–H stretching vibration. However, all the calculated wave numbers show positive deviation

N–H vibrations It has been observed that the presence of N–H in various molecules may be correlated with a constant occurrence of absorption bands whose positions are slightly altered from one compound to another this is because of atomic group which vibrates independently from the other groups in the molecule and has its own frequency. In all the hetro cyclic compounds the N–H stretching vibrations occur in the region 3500–3300 cm1 [38–40]. The position of absorption in this region depends upon the degree of hydrogen bonding and physical state of the sample. In the present investigation the N–H stretching vibrations have been found at 3424 cm1 in IR and at 3421 cm1 in Raman spectrum with the 100% of TED contribution. Theoretically computed N–H vibrations by B3LYP method of scaled values approximately coincides with experimental value. C–C vibrations The carbon–carbon stretching modes of the phenyl group are expected in the range from 1650–1200 cm1 The actual position of these modes are determined not so much by the nature of the substituent’s but by the form of substitution around the ring [41]. In the present case, the C–C stretching vibrations are found at 1604, 1021, 1010, 822, 798 cm1 in FTIR and four bands assigned at 1645, 1020, 1013, 820 cm1 in FT-Raman spectrum. When compared to the literature range cited above, there is a considerable decrease in frequencies which is also worsening with the increase of mass of substitutions (O–H). In the present work, the bands are identified at 1017, 671, 631, 630 cm1 in both spectra assigned for C–C–C in-plane bending and one O–C–C in plane bending are assigning at 335 cm1 in FT-Raman spectrum. These assignments are in line with the assignments proposed by the literature [42]. The bands observed at 570, 416 cm1 in Raman is assigned for C–N–C tri-gonal bending and one Raman band with medium intensity found at 320 cm1 is assigned for C–N–C ring breathing mode. These assignments are in line with literature [43,44]. The aromatic C–H in-plane and out of plane bending vibrations have substantial overlapping with the ring C–C–C in-plane and out of plane bending modes, respectively. Other molecular properties NBO analysis NBO analysis provides the most accurate possible ‘natural Lewis structure’ picture of u, because all the 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 NBO analysis [45]. The interaction result is the 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 E2 associated with the delocalization i ? j is estimated as

E2 ¼ DEij ¼

qi ðF ij Þ2 ej  ei

where qi is the donor orbital occupancy, ej and ei are diagonal elements and Fij is the off diagonal NBO Fock matrix element. Natural bond orbital analysis provides an efficient method for studying intra and intermolecular bonding and interaction among

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Fig. 8. Mulliken population analysis chart of SSMPL.

Table 7 The Thermodynamic parameters of SSMPL along with the Zero point energy calculated at B3LYP methods with 6-31G (d, p) and 6-311++G(d,p) basis sets. Parameter

B3LYP/6-311++G(d,p)

B3LYP/6-31G(d,p)

Zero-point correction Gibbs free energy Energy Enthalpy Total Translational Rotational Vibrational Thermal free energies Zero point vibrational energy (kcal mol1)

0.243658 0.204831 0.248316 0.24671 165.6 0.889 0.889 155.992 519.664230 142.30456

0.235938 0.197796 0.247966 0.24891 155.601 0.889 0.889 153.823 519.880061 148.05306

Rotational constants (GHz) A B C Dipole moment (Debye)

lx ly lz ltotal

1.49554 0.62362 0.52463 0.012 0.3541 1.030 1.0892

1.49258 0.62362 0.52463 0.014 0.3391 1.018 1.0731

bonds, and provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital and the interacting stabilization energy resulting from the second-order micro-disturbance theory are reported [46,47]. The larger E2 value, 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 orbital and formally unoccupied (anti-bond or Rydgberg) non-Lewis NBO orbital corresponds to a stabilizing donor–acceptor interaction. NBO analysis has been performed on the molecule at the B3LYP/6-31G(d,p) level in order to elucidate the intra-molecular, re-hybridization and delocalization of electron density within the molecule. The intra-molecular interaction is formed by the orbital overlap between r(C–C) and r(C– C) bond orbital which results in intra-molecular charge transfer (ICT) causing stabilization of the system. These interactions are ob-

served as increase in electron density (ED) in C–C anti-bonding orbital that weakens the respective bonds [48]. The most important interaction energy in this molecule, is the electron donating from C5–C10 (r) to the anti-bonding C9–H22 (r) resulting stabilization of 3.43 kJ/mol. The same C5–C10 (r) with C5–C6 (r) leads to a strong stabilization of 7.84 kJ/mol. NBO analysis clearly manifests the evidences of the intra-molecular charge transfer from p(C5–C10) to p(C6–C7) anti-bonding Orbital’s as shown in Table 4, that clearly shows stabilization energy of 33.39 kJ/mol. The same leads to a strong stabilization energy of 44.39 kJ/mol of (C8–C9). The r electron delocalization is maximum around C1–C2, N11–H24, C1–C5 which is revealed by the ED of the conjugated r bond. similarly p electron delocalization is maximum of C8–C9. From NBO analysis, the interaction C6–C7 ? C5– C10 observed in SSMPL shows a large amount of stabilization energy of about 44.54 kJ/mol. The calculation of effective atomic charges plays an important role in the application of quantum mechanical calculations to molecular systems.

Molecular electrostatic potential analysis Electrostatic potential maps, also known as electrostatic potential energy maps, or molecular electrical potential surfaces, illustrate the charge distributions of molecules three dimensionally. The purpose of finding the electrostatic potential is to find the reactive site of a molecule. These maps allow us to visualize variably charged regions of a molecule. Knowledge of the charge distributions can be used to determine how molecules interact with one another. Molecular electrostatic potential (MESP) mapping is very useful in the investigation of the molecular structure with its physiochemical property relationships [49–52]. Total SCF electron density surface mapped with molecular electrostatic potential (MESP) of SSMPL are shown in Fig. 6. The molecular electrostatic potential surface MESP which is a 3D plot of electrostatic potential mapped onto the iso-electron density surface simultaneously displays molecular shape, size and electrostatic potential values. The co lour scheme for the MESP surface is red-electron rich or partially negative charge; blue-electron deficient or partially positive charge; light blue-slightly electron deficient region; yellow-slightly electron rich region, respectively. Areas of low potential, red are characterized by an abundance of electrons. Areas of high potential,

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blue are characterized by a relative absence of electrons. Nitrogen has a higher electro negativity value, it would consequently have a higher electron density around them. Thus the spherical region that corresponds to nitrogen atom would have a red portion on it. The MESP of SSMPL clearly indicates the electron rich centers of nitrogen, oxygen and the areas covering the C1, C2, C4, C10 atoms. The MESP map shows that the negative potential sites are on electronegative atoms as well as the positive potential sites are around the hydrogen atoms. These sites give information about the region from where the compound can have non-covalent interactions. HOMO LUMO analysis Many organic molecules that contain conjugated p electrons are characterized by hyper polariz abilities and were analyzed by means of vibrational spectroscopy [53,54]. In most cases, even in the absence of inversion symmetry, the strongest bands in the Raman spectrum are weak in the IR spectrum and vice versa. But the intra-molecular charge transfer from the donor to accepter group through a single–double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making IR and Raman activity strong at the same time. The experimental spectroscopic behavior described above is well accounted by ab initio calculations in conjugated systems that predict exceptionally large Raman and infrared intensities for the same normal modes [53]. It is also observed in our title molecule the bands in FTIR spectrum have their counterparts in Raman, which shows that the relative intensities in IR and Raman spectra are comparable resulting from the electron cloud movement through p conjugated frame work from electron donor to electron acceptor groups. The analysis of the wave function indicates that the electron absorption corresponds to the transition from the ground to the first excited state and is mainly described by oneelectron excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). The LUMO of p nature (i.e., benzene ring) is delocalized over the whole C–C bond. By contrast, the HOMO is located over methyl groups, consequently the HOMO ? LUMO transition implies an electron density transfer to C–C bond of the benzene ring from methyl groups. Moreover these orbital significantly overlap in their position for SSMPL. The atomic orbital compositions of the frontier molecular orbital are sketched in Fig. 7. The HOMO–LUMO energy gap of SSMPL was calculated at the B3LYP/6-311++G(d,p) and B3LYP/6-31G(d,p) levels and is shown in Table 5, reveals that the energy gap reflect the chemical activity of the molecule. LUMO as an electron acceptor represent the ability to obtain an electron, HOMO represents the ability to donate an electron. Therefore, The molecular orbitals shows that the electron density in the HOMO mostly centered on the heterocyclic moiety and part of the benzene ring while in LUMO the electron density predominantly located on the benzene ring; indicating a charge transfer of the type p ? p upon excitation. Moreover, a lower HOMO–LUMO energy gap explains the fact that eventual charge transfer interaction is taking place within the molecule. Mulliken population analysis The Mulliken atomic charges are calculated by determining the electron population of each atom as defined by the basis function [55]. The Mulliken atomic charges of SSMPL molecule calculated by B3LYP using different basis sets 6-31G(d,p), 6-311++G(d,p). Calculation of effective atomic charges plays an important role in the application of quantum chemical calculations to molecular systems. Our interest here is in the comparison of different methods to describe the electron distribution in SSMPL as broadly as possible, and assess the sensitivity, the calculated charges to changes in

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(i) the choice of the basis set; (ii) the choice of the quantum mechanical method. Mulliken charges, calculated the electron population of each atom defined in the basic functions. The Mulliken charges calculated at different levels and at same basis set are listed in Table 6. The results can, however, better represent in graphical form as given Fig. 8. The charges depending on basis set are changed due to polarizability. The H18 and H24 atoms have more positive charges both B3LYP/6-31G(d,p) and B3LYP/6311++G(d,p), whereas the H24 atom has more positive charge than the other atoms. This is due to the presence of electronegative oxygen atom; the hydrogen atoms attract the positive charge from the oxygen atoms The C2 and O4 atoms by B3LYP methods are more negative charges than the other atoms due to electron accepting substitutions at that position in SSMPL. The result suggests that the atoms bonded to O atom and all H atoms are electron acceptor and the charge transfer takes place from O to H in SSMPL. Thermodynamic properties Several calculated thermodynamic parameters, rotational constants, rotational Enthalpy, Gibbs free energy and dipole moment have been presented in Table 7. Scale factors have been recommended [56] for accurate reductions in determining the Zero-Point Vibration Energies (ZPVEs) and the entropy, the variations in the PVEs seem to be significant. The biggest value ZPVE of SSMPL is 148.90456 kcal/mol obtained at B3LYP/6-311++G(d,p) whereas the smallest value is 148.05306 cal/mol obtained at B3LYP/631G(d,p). The total energies are found to decrease with the increase of the basis set dimension and the change in the Gibbs free energy of SSMPL at room temperature at different basis set are only marginal. The dipole moment of the molecule was also calculated by B3LYP method with two basis sets. Dipole moment reflects the molecular charge distribution and is given as a vector in three dimensions. Therefore, it can be used as descriptor to depict the charge movement across the molecule depending upon the centers of positive and negative charges. Dipole moments are strictly determined for neutral molecules. For charged systems, its value depends on the choice of origin and molecular orientation. As a result of B3LYP calculations the highest dipole moments were observed for B3LYP/6-311++G(d,p) whereas the smallest one was observed for B3LYP/6-31G(d,p) in SSMPL. Conclusions A complete vibrational frequency assignment of SSMPL has been carried out using FTIR and FT Raman spectrum. The equilibrium geometries, harmonic vibrational frequencies, IR intensities of the title compound were determined and analyzed by B3LYP levels of theory utilizing 6-31G(d,p) and 6-311++G(d,p) basis sets. The observed and calculated fundamental frequencies by B3LYP method using 6-311++G(d,p), 6-31G(d,p) basis sets shows similar profiles in both position and intensities making normal mode assignments with confidence. Total energy distributions (TEDs) suggest that several normal modes are coupled in varying degrees. The electric dipole moment, polarizabilities and the hyperpolarizabilities of the compound studied that have been calculated by B3LYPmethod with 6-31G(d,p) and 6-311++G(d,p) basis sets. NBO result SSMPL reflects the charge transfer mainly due to C-C group. HOMO and LUMO energy gap explains the shows eventual charge transfer interactions taking place within the molecule. The calculated atomic charges for the SSMPL using Mulliken population analysis in all cases are different by values. It could be concluded that population analyses is suitable for the estimation of the changes of the atomic charges. This study demonstrates that scaled

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