Comparative Theoretical Studies on Natural Atomic Orbitals
Indian Journal of Pure & Applied Physics Vol. 51, March 2013, pp. 178-184
Comparative theoretical studies on natural atomic orbitals, natural bond orbitals and simulated UV-visible spectra of N-(methyl)phthalimide and N-(2 bromoethyl)phthalimide
V Balachandran1,*, T Karthick2, S Perumal3 & A Nataraj4 1P G & Research Department of Physics, Arignar Anna Government Arts College, Musiri, Tiruchirapalli 621 211, Tamil Nadu, India 2Department of Physics, Vivekanandha College for Women, Tiruchengode 637 205, Tamil Nadu, India 3P G & Research Department of Physics, S T Hindu College, Nagarcoil 629 002, Tamil Nadu, India 4P G & Research Department of Physics, Thanthai Hans Roever College, Perambalur 621 212, Tamil Nadu, India *E-mail: [email protected] Received 10 October 2012; revised 3 December 2012; accepted 11 January 2013
The charge delocalization patterns of phthalimide derivatives such as N-(methyl)phthalimide and N-(2-bromoethyl)- phthalimide have been performed with the help of natural bond orbital (NBO) analyses and simulated UV-visible spectra. The second order perturbation energies of the most interacting NBOs and the population of electrons in core, valance and Rydberg sub-shells have been predicted by density functional theory (DFT) computations in GAUSSIAN 03W software package. In the present study, the natural atomic orbital occupancies showed the presence of charge delocalization within the molecule. The natural hybrid atomic orbital studies enhance us to know about the type of orbitals and its percentage of s-type and p-type character. In addition, the excited electronic transitions along with their absorption wavelengths, oscillator strengths and excitation energies for the gaseous phase of the title molecules have been computed at TD-DFT/B3LYP/6- 311++G(d,p) method. The energetic behaviour of the compound in different solvent medium (water, ethanol, and methanol) has been examined by applying polarizable continuum model (PCM). The complete molecular orbital simulations and theoretical UV-visible spectra have been carried out in this study which yield better understanding of charge delocalization pattern and stability of the title molecules to a greater extent. Keywords: Charge transfer, Density functional theory, Natural bond orbital, Natural atomic orbital, Simulated UV-visible spectra
1 Introduction N-(methyl)phthalimide and N-(2-bromoethyl)phtha- In recent years, the charge delocalization patterns limide to estimate their delocalization patterns of and the chemical reactivity of polyatomic molecules charge, electron densities of atoms and excited have been focused widely. The information about the electron transition. charge delocalization and the chemical reactivity is Phthalimide and its N-substituted phthalimide being helpful to the drug designers to design new type derivatives are found in wide applications in of drugs. The natural bond orbital (NBO) is an pharmacy, medicinal chemistry and industry. In effective tool for the elucidation of residual resonance pharmaceutical, they are being used as an delocalization effects of a molecule and it also intermediate material. In medical field, the illustrates the deciphering of the molecular wave phthalimide analogues are being used in the synthesis function in terms of Lewis structures, charge, bond of anti-microbial activity, androgens and other agents order, bond type, hybridization, resonance, donor- for treating tumor necrosis factor8. Apart from their acceptor interactions, etc1. Therefore, the NBO well recognized applications in pharmacy, the analysis of certain pharmaceutical compounds has phthalimide analogues take an important role as anti- been performed by various spectroscopists2-7. For the convulsant, anti-inflammatory, analgesic, hypoli- complete assignments of charge delocalization pidimic and immunomodulatory activities9 in patterns of a molecule, the allowed excited electron medicinal chemistry. Certain phthalimide derivatives transitions and maximum absorption wavelenghts are are used as herbicides for reducing bacterial to be measured. Thus, in the present study, we have contamination. In industry, they are being widely used performed NBO and the simulated UV-Visible in the production of pesticides, dyes, plastics, high spectral analysis on the electronic structures of performance ion exchange resins, surfactants. In BALACHANDRAN et al.: NATURAL ATOMIC ORBITALS OF PHTHALIMIDE 179
particular, N-(methyl) phthalimide (abbreviated as Moreover, the information about excited electron NMP) and N-(2-bromoethyl)phthalimide (abbreviated transitions along with their absorption wavelengths, as NBEP) are being most extensively used as an excitation energies and oscillator strengths was intermediate material for the synthesis of a drug10,11. predicted at TD-DFT/B3LYP method with In our previous work, we have studied their 6-311++G(d,p) basis set. The solvent effects of the vibrational characteristics, non-linear optical molecules have also been examined by using properties and thermodynamic parameters10,11. To polarizable continuum model (PCM) with establish our previous work, the natural population TD-DFT/B3LYP/6-311++G(d,p) method. The analysis, natural bond orbital analysis and simulated simulated UV-Visible spectra of both gaseous and in UV-Visible spectra of NMP and NBEP have been different solvent phases have also been provided. performed in the present work. 3 Results and Discussion 2 Computational Details 3.1 Natural atomic orbitals Initially, the electronic structures of these The occupancies and energies of bonding molecules were optimized by solving self-consistent molecular orbitals of both the title molecules are field equation and the optimized structures predicted at B3LYP/6-311++G(d,p) level of theory corresponding to a single point minima were obtained and presented in Table 1. The variations in by density functional B3LYP method with standard occupancies and energies of NBEP in comparison high level 6-311++G(d,p) basis set. In order to obtain with those of NMP directly give the evidence for the the complete information regarding population of delocalization of charge upon substitution and this electrons in sub-shells of atomic orbitals and leads to the variation of bond lengths between the delocalization of charge and electron densities of molecules as shown in Figs 1 and 2. atoms in the title molecules, the molecular orbital calculations have been carried out using NBO 3.1 3.2 Natural population analysis program12 as employed in Gaussian 03W software The natural population analysis14 performed on the package13 at the DFT/B3LYP/6-311++G(d,p) level. electronic structures of NMP and NBEP clearly
Table 1 — Comparison of occupancies and energies of bonding molecular orbitals between NMP and NBEP
Atomic orbitalsa NMP Atomic orbitalsb NBEP Occupancies (e) Energies (a.u) Occupancies (e) Energies (a.u)
BD (C1−N2) 1.9855 −0.8108 BD (C1−N2) 1.9839 −0.8344 BD (C1−C8) 1.9708 −0.6735 BD (C1−C8) 1.9764 −0.7162 BD (C1−O10) 1.9945 −1.1062 BD (C1−O10) 1.9922 −0.8005 BD (N2−C3) 1.9855 −0.8108 BD (N2−C3) 1.9836 −0.8387 BD (N2−C11) 1.9900 −0.7694 BD (N2−C11) 1.9880 −0.7865 BD (C3−C9) 1.9708 −0.6735 BD (C3−C9) 1.9773 −0.7179 BD (C3−O15) 1.9945 −1.1061 BD (C3−O18) 1.9923 −0.8191 BD (C4−C5) 1.9787 −0.7211 BD (C4−C5) 1.9764 −0.7215 BD (C4−C9) 1.9765 −0.7364 BD (C4−C9) 1.9751 −0.7481 BD (C4−H16) 1.9796 −0.5429 BD (C4−H19) 1.9786 −0.5508 BD (C5−C6) 1.9808 −0.7256 BD (C5−C6) 1.9813 −0.7376 BD (C5−H17) 1.9805 −0.5417 BD (C5−H20) 1.9805 −0.5547 BD (C6−C7) 1.9787 −0.7211 BD (C6−C7) 1.9787 −0.7238 BD (C6−H18) 1.9805 −0.5417 BD (C6−H21) 1.9804 −0.5539 BD (C7−C8) 1.9765 −0.7364 BD (C7−C8) 1.9767 −0.7496 BD (C7−H19) 1.9796 −0.5429 BD (C7−H22) 1.9786 −0.5519 BD (C8−C9) 1.9643 −0.7147 BD (C8−C9) 1.9559 −0.6815 BD (C11−H12) 1.9873 −0.5307 BD (C11−H12) 1.9712 −0.5540 BD (C11−H13) 1.9886 −0.5318 BD (C11−H13) 1.9800 −0.5500 BD (C11−H14) 1.9886 −0.5318 BD (C11−C14) 1.9875 −0.6559 BD (C14−H15) 1.9868 −0.5503 BD (C14−H16) 1.9846 −0.5554 BD (C14−Br17) 1.9870 −0.6327 a For numbering of atoms of NMP refer Fig. 1 b For numbering of atoms of NBEP refer Fig. 2
180 INDIAN J PURE & APPL PHYS, VOL 51, MARCH 2013
Fig. 1 — Optimized molecular structure of NMP
Fig. 2 — Optimized molecular structure of NBEP describes the distribution of electrons in various sub- electron. Whereas, the most electropositive atoms shells of their atomic orbitals. The accumulation of such as; C1 and C3 have a tendency to accept an charges on the individual atom and the accumulation electron. Further, the natural population analysis of electrons in the core, valence and Rydberg showed that 84 electrons in the NMP molecule are sub-shells are also presented in Table 2. In the case of distributed on the sub-shells as follows: NMP, the most electronegative charge of −0.5589 e is accumulated on O10 and O15 atom and −0.5146 e is Core : 23.9907 (99.9614% of 24) accumulated on the nitrogen atom N2. According to Valence : 59.7553 (99.5922% of 60) an electrostatic point of view of the molecule, these electronegative atoms have a tendency to donate an Rydberg : 0.2540 (0.3023% of 84) BALACHANDRAN et al.: NATURAL ATOMIC ORBITALS OF PHTHALIMIDE 181
Table 2 — Accumulation of natural charges, population of electrons in core, valance, Rydberg orbitals of NMP and NBEP
NMP NBEP Atoma Charge (e) Natural population (e) Total (e) Atomb Charge (e) Natural population (e) Total (e) core valence Rydberg Core valance Rydberg
C1 0.6925 1.9993 3.2655 0.0428 5.3076 C1 0.6608 1.9989 3.3080 0.0322 5.3392 N2 −0.5146 1.9992 5.5002 0.0152 7.5146 N2 −0.5009 1.9991 5.4848 0.0170 7.5009 C3 0.6924 1.9993 3.2655 0.0428 5.3076 C3 0.6429 1.9989 3.3246 0.0336 5.3571 C4 −0.1608 1.9991 4.1443 0.0175 6.1608 C4 −0.1231 1.9988 4.1055 0.0188 6.1231 C5 −0.1803 1.9992 4.1640 0.0172 6.1803 C5 −0.1798 1.9992 4.1631 0.0175 6.1798 C6 −0.1803 1.9992 4.1639 0.0172 6.1803 C6 −0.1785 1.9992 4.1628 0.0165 6.1785 C7 −0.1608 1.9991 4.1443 0.0175 6.1608 C7 −0.1361 1.9991 4.1200 0.0170 6.1361 C8 −0.1107 1.9989 4.0951 0.0167 6.1107 C8 −0.1195 1.9989 4.1049 0.0158 6.1195 C9 −0.1106 1.9989 4.0951 0.0167 6.1106 C9 −0.1206 1.9989 4.1040 0.0176 6.1206 O10 −0.5589 1.9998 6.5474 0.0117 8.5589 O10 −0.5984 1.9999 6.5922 0.0063 8.5984 C11 −0.3649 1.9993 4.3510 0.0146 6.3649 C11 −0.1620 1.9992 4.1441 0.0187 6.1620 H12 0.2008 0.0000 0.7975 0.0018 0.7993 H12 0.2166 0.0000 0.7810 0.0025 0.7834 H13 0.2191 0.0000 0.7792 0.0018 0.7809 H13 0.2181 0.0000 0.7800 0.0023 0.7819 H14 0.2190 0.0000 0.7792 0.0018 0.7810 C14 −0.4518 1.9991 4.4351 0.0176 6.4518 O15 −0.5589 1.9998 6.5474 0.0117 8.5589 H15 0.2252 0.0000 0.7722 0.0026 0.7748 H16 0.2273 0.0000 0.7707 0.0020 0.7727 H16 0.2177 0.0000 0.7802 0.0021 0.7823 H17 0.2112 0.0000 0.7872 0.0016 0.7888 Br17 0.1232 27.9992 6.8508 0.0268 34.8768 H18 0.2112 0.0000 0.7872 0.0016 0.7888 O18 −0.6145 1.9999 6.6022 0.0124 8.6145 H19 0.2273 0.0000 0.7707 0.0020 0.7727 H19 0.2281 0.0000 0.7699 0.0019 0.7719 H20 0.2110 0.0000 07873 0.0017 0.7890 H21 0.2112 0.0000 0.7871 0.0017 0.7888 H22 0.2303 0.0000 0.7678 0.0020 0.770 aFor numbering of atoms of NMP refer Fig. 1 bFor numbering of atoms of NBEP refer Fig. 2
However, in the case of NBEP, the most the delocalization patterns of electron density (ED) electronegative charges of −0.6145 and −0.5984 e are from the principal occupied Lewis-type (bond or lone accumulated on O18 and O15 atoms. On the other hand, pair) orbitals to unoccupied non-Lewis (anti-bonding the atoms C1 (0.6608 e) and C3 (0.6429 e) are carrying or Rydberg) orbitals. Table 3 lists the occupancies and the most electropositive charges. In view of NMP, the energies of most interacting NBO’s along with their 16 electronegative atoms O10 and O15 are of equal in percentage of hybrid atomic orbital contribution. magnitude and also the magnitudes of electropositive The percentage of hybrid atomic orbitals of oxygen atoms C1 and C3 are the same. The substituent effect lone pair atoms O10, O15 of NMP showed that they are may cause a change in the magnitude of these charges partially contributed to both s-type and p-type sub- observed in NBEP. In particular, the −CH2Br group shells. In contrast, all the anti-bonding orbitals of substituted in place of hydrogen H13 atom of NMP NMP are mainly contributed to p-type sub-shell. makes significant variations in the magnitude of However in the case of NBEP, all the lone pair atoms natural charges on C1, C3 and O10, O18. As a result, the O10, O18 and Br17 are predominantly contributed to NBEP molecule has more tendencies to donate as s-sub-shell and all the anti-bonding orbitals are well as accept the electron than NMP. Further, the contributed to p-type sub-shell. natural population analysis showed that 126 electrons The interactions result in a loss of occupancy from in the NBEP molecule are distributed on the the localized NBO of the idealized Lewis structure sub-shells as follows: into an empty Non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy, E(2) Core : 53.9883 (99.9783% of 54) associated with the delocalization i j is estimated Valence : 71.7270 (99.6209% of 72) as:
Rydberg : 0.2846 (0.2259% of 126) F() ij 2 E(2) = ∆ E = q …(1) ij i ε− ε 3.3 Natural bond orbital analysis j i 15 The natural bond orbital (NBO) analysis of NMP where qi is the donor orbital occupancy, εi and εj are and NBEP molecules are being performed to estimate diagonal elements and F(i,j) is the off diagonal NBO 182 INDIAN J PURE & APPL PHYS, VOL 51, MARCH 2013
Table 3 — Natural atomic orbital occupancies of most interacting NBO’s of NMP and NBEP along with their percentage of hybrid atomic orbitals
NMP NBEP a b c b Parameters Occupancies (e) Hybrid AO (%) Parameters Occupancies (e) Hybrid AO (%)
0.71 0.30 LP(1) O10 1.9794 sp s(58.55) p(41.43) LP(1) O10 1.9850 sp s(76.97) p(23.02) 0.71 0.16 LP(1) O15 1.9794 sp s(58.55) p(41.43) LP(1) Br17 1.9967 sp s(86.27) p(13.73) ∗ 2.40 0.30 BD (1) 0.0914 sp (C1) s(29.41) p(70.47) LP(1) O18 1.9829 sp s(76.76) p (23.23) 2.03 C1−N2 sp (N2) s(32.96) p(66.99) ∗ 1.75 ∗ 2.36 BD (1) 0.0717 sp (C1) s(36.41) p( 63.54) BD (1) C1−N2 0.0613 sp (C1) s(29.73) p(70.12) 2.44 2.05 C1−C8 sp (C8) s(29.02) p(70.93) sp (N2) s(32.74) p(67.21) ∗ 1.94 ∗ 1.60 BD (1) 0.0107 sp (C1) s(33.99) p(65.86) BD (1) C1−C8 0.0417 sp (C1) s(38.41) p(61.53) 1.41 2.23 C1−O10 sp (O10) s(41.48) p(58.39) sp (C8) s(30.93) p(69.02) 2.03 ∗ 2.16 BD*(1) 0.0914 sp (N2) s(32.96) p(66.99) BD (1) C1−O10 0.0166 sp (C1) s(31.63) p(68.24) 2.40 3.42 N2−C3 sp (C3) s(29.41) p( 70.47) sp (O10) s(22.58) p(77.33) 1.94 2.05 BD*(1) 0.0198 sp (N2) s(34.01) p(65.97) BD*(1) N2−C3 0.0569 sp (N2) s(32.82) p(67.14) 3.32 2.33 N2−C11 sp (C11) s(23.13) p(76.74) sp (C3) s(29.95) p(69.91) 1.75 1.91 BD*(1) 0.0717 sp (C3) s(36.41) p(63.54) BD*(1) N2−C11 0.0287 sp (N2) s(34.37) p(65.61) 2.44 3.63 C3−C9 sp (C9) s(29.02) p(70.93) sp (C11) s(21.57) p(78.28) ∗ 1.94 1.59 BD (1) 0.0107 sp (C3) s(33.99) p(65.86) BD*(1) C3−C9 0.0398 sp (C3) s(38.55) p(61.40) 1.41 2.21 C3−O15 sp (O15) s(41.48) p(58.39) sp (C9) s(31.13) p(68.82) ∗ 2.19 BD (1) C3−O18 0.0228 sp (C3) s(31.26) p(68.60) 3.33 sp (O18) s(23.10) p(76.81) 2.56 BD*(1) C11−C14 0.0164 sp (C11) s(28.10) p(71.86) 2.53 sp (C14) s(28.32) p(71.63) aFor numbering of atoms of NMP refer Fig. 1 bPercentage of s-type and p-type subshells of an atomic orbitals are given in their respective brackets c For numbering of atoms of NBEP refer Fig. 2
Table 4 — Second-order perturbation energy (E(2), kcal/mol) between donor and acceptor orbitals of NMP and NBEP calculated at B3LYP/6-311++G(d,p) level of DFT theory.
NMPa NBEPb Donor (i) → Acceptor (j) E(2) kcal/mol Donor (i) → Acceptor (j) E(2) kcal/mol LP(1) N →BD∗(2) C −O 49.79 LP(1) N →BD∗(2) C −O 59.10 2 ∗ 1 10 2 ∗ 1 10 LP(1) N2 →BD (2) C3−O15 49.79 LP(1) N2 →BD (2) C3−O18 64.91 LP(1) N →BD∗(1) C −H 6.26 LP(1) N C→BD∗( −H ) 4.17 2 ∗ 11 12 2 ∗ 11 12 LP(1) N2 →BD (1) C11−H13 1.49 LP(1) N2C→BD ( 11−H13) 4.17 LP(1) N →BD∗(1) C −H 1.49 LP(1) O →BD∗(1) C −N 1.45 2 ∗ 11 14 10 ∗ 1 2 LP(1) O10 →BD (1) C1−N2 1.36 LP(1) O10 →BD (1) C1−C8 2.47 LP(1) O →BD∗(1) C −C 2.53 LP(2) O → BD∗(1) C −N 14.84 10 ∗ 1 8 10 ∗ 1 2 LP(2) O10 → BD (1) C1−N2 28.84 LP(2) O10 → BD (1) C1−C8 7.35 LP(2) O → BD∗(1) C −C 19.45 LP(2) Br → BD∗ (1) C −H 1.00 10 ∗ 1 8 17 ∗ 11 12 LP(1) O15 →BD (1) N2−C3 1.36 LP(2) Br17 → BD (1) C11−C14 3.41 LP(1) O →BD∗(1) C −C 2.53 LP(2) Br → BD∗ (1) C −H 0.62 15 ∗ 3 9 17 ∗ 11 15 LP(2) O15 →BD (1) N2−C3 28.84 LP(2) Br17 → BD (1) C11−H16 1.05 LP(2) O →BD∗(1) C −C 19.45 LP(3) Br → BD∗ (1) C −O 1.23 15 3 9 17 ∗ 3 18 LP(3) Br17→ BD (2) C3−O18 6.97 LP(3) Br → BD∗ (1) C −H 3.24 17 ∗ 11 15 LP(3) Br17→ BD (1) C11−H16 1.85 LP(1) O → BD∗(1) N −C 1.75 18 ∗ 2 3 LP(1) O18→ BD (1) C3−C9 1.95 LP(1) O → BD∗(2) C −O 0.61 18 ∗ 3 18 LP(2) O18→ BD (1) N2−C3 13.11 LP(2) O → BD∗(1) C −C 6.95 18 ∗ 3 9 LP(2) O18 → BD (1) C14−H16 1.30 aFor numbering of atoms of NMP refer Fig. 1 bFor numbering of atoms of NBEP refer Fig. 2
Fock matrix element. The NBO analysis provides an Table 4 presents the second order perturbation efficient method for studying intra-and intermolecular energies (often called as the stabilization energies or bonding and also provides a convenient basis for interaction energies) of most interacting NBOs of investigating charge transfer or conjugative NMP and NBEP. The second order perturbation interactions in molecular systems17. energies corresponding to the hyperconjugative BALACHANDRAN et al.: NATURAL ATOMIC ORBITALS OF PHTHALIMIDE 183
∗ interactions of NMP such as; LP(1) N2 →BD (2) polarizable continuum model (PCM) TD-DFT method ∗ C1−O10, LP(1) N2 →BD (2) C3−O15, LP(2) O10→ with B3LYP/6-311++G(d,p) basis set. The calculated ∗ ∗ BD (1) C1−N2, LP(2) O10 → BD (1) C1−C8, LP(2) absorption wavelengths, oscillator strengths, ∗ ∗ excitation energies of molecule in gas phase as well as O15 →BD (1) N2−C3, LP(2) O15 →BD (1) C3−C9, are considerably very large. The aforesaid in water, ethanol and methanol solvent medium are hyperconjugative interactions are the most responsible presented in Table 5 and theoretically simulated for the stability of NMP. Parenthesized label numbers UV-Visible spectrum of NMP and NBEP in different such as BD(1), BD(2) distinguish multiple bonds solvents as shown in Figs 4 and 5, respectively for between the same atoms and similar LP(1), LP(2) comparing their energetic behaviour. In the electronic labels distinguish multiple lone pair orbitals at each center. In the case of NBEP, the most significant hyperconjugative interactions of 64.91 and ∗ 59.10 kcal/mol are obtained for LP(1) N2 →BD (2) ∗ C3−O18 and LP(1) N2 →BD (2) C1−O10, respectively. In NBEP, a few of non-bonding interactions of 1.23 ∗ and 6.97 kcal/mol are obtained for LP(3) Br17→ BD ∗ (1) C3−O18, LP(3) Br17 → BD (2) C3−O18. Also, such non-bonding interactions increase the stability of a molecule as well.
3.4 Theoretical UV-Visible spectra and solvent effect In order to investigate the electron transition between the energy levels, the lowest singletsinglet spin allowed excited states are to be taken into Fig. 3 — Simulated UV-visible spectra in the gaseous phase of account. In the present study, the maximum NMP and NBEP absorption wavelengths ((max), excitation energies (DE) and oscillator strengths (f) of the title molecules in the gaseous phase are computed using TD-DFT/B3LYP/6-311++G(d,p) method. The simulated UV-Visible spectrum of both the molecules in the gaseous phase is shown in Fig. 3. The NMP molecule has three maximum absorption peaks of very low oscillator strengths (say ~0.0001a.u) [Fig. 3]. The observed peaks in the spectrum may cause one electron excitation from HOMOLUMO, HOMO−1LUMO and HOMO−2LUMO while in the case of NBEP; these peaks have been identified at 659.6l, 457.22 and 379.41nm, respectively.
The solvent effect on the absorption wavelengths Fig. 4 — Calculated UV-visible spectra of NMP in different and excitation energies are also examined by applying solvents
Table 5 — Calculated maximum absorption wavelengths ((max), excitation energies (E) and oscillator strengths (f) of NMP and NBEP in gas phase and in different solvents by TD-DFT/B3LYP/6-311++G(d,p) method
Molecule Excitation Gas phase Water Ethanol Methanol
(max E f (max E f (max E f (max E f (nm) (eV) (a.u) (nm) (eV) (a.u) (nm) (eV) (a.u) (nm) (eV) (a.u)
NMP H L 322.71 3.8420 0.0001 311.38 3.9818 0.0010 310.67 3.9908 0.0009 310.89 3.9880 0.0009 H−1 L 298.71 4.1506 0.0001 306.15 4.0498 0.0002 307.24 4.0354 0.0002 306.82 4.0409 0.0002 H−2 L 279.26 4.4398 0.0002 281.89 4.3983 0.0772 281.47 4.4049 0.0776 281.55 4.4037 0.0761 NBEP H L 659.61 1.8797 0.0806 629.85 1.9685 0.0973 632.28 1.9609 0.0983 630.76 1.9656 0.0969 H−1 L 457.22 2.7117 0.0013 422.83 2.9322 0.0022 426.06 2.9100 0.0022 424.65 2.9197 0.0021 H−2 L 379.41 3.2679 0.0010 389.02 3.1871 0.0035 387.05 3.2033 0.0035 387.87 3.1966 0.0034
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s-type and p-type sub-shells and their hybridization details. The second order perturbation results obtained in this study showed the most significant hyperconjugative interactions responsible for the stability of a molecule. It also showed that a non- bonding interaction taking place from the lone pair bromine atom Br17 to anti-bonding C1-O18 increases the stability of NBEP molecule. The excited state electron transition along with their maximum absorption wavelengths, vertical excitation energies and oscillator strengths are predicted at PCM of TD-DFT/B3LYP/6-311++G(d,p) method. From the electronic spectrum of NMP and NBEP, the information about the allowed and forbidden
transitions is found and the solvent effect is also Fig. 5 — Calculated UV-visible spectra of NBEP in different examined. solvents spectrum of NMP, the strong intensity peaks at the References 1 Glendening E D, Landis C R & Weinhold F, WIREs Comput maximum absorption wavelength of 281.89 (water), Mol Sci, 2 (2012) 1. 281.47 (ethanol) and 281.55 (methanol) are caused by 2 Magdaline J D & Chithambarathanu T, Indian J Pure & Appl n4* transitions18,19 and the smaller intensity bands Phys, 50 (2012) 7. calculated above 300 nm in all the phases of NMP are 3 Zhou Z R, Hong L X & Zhou Z X, Indian J Pure & Appl Phys, 50 (2012) 719. strongly forbidden and therefore, the value of its 4 Karthick T, Balachandran V, Perumal S & Natraj A, J Mol oscillator strength nearly equals to zero. In the case of Struct, 1005 (2011) 192. NBEP, an oscillator strength of nearly ~0.097 au for 5 Hong L X, Zhou Z R & Zhou Z X, Indian J Pure & Appl the maximum absorption wavelengths 629.85, 632.28 Phys, 50 (2012) 697. and 630.76 nm, respectively for the molecule in 6 Balachandran V, Karthick T, Perumal S & Natraj A, Spectrochim. Acta, 92A (2012) 137. water, ethanol and methanol solvents belonging to 7 Chandra S, Saleem H, Sebastian S & Sundaraganesan N, anelectron transition from HOMO to LUMO. The Spectrochim Acta, 78A (2011) 1515. other excitation wavelengths of less intensity peaks 8 Krishnakumar V, Balachandran V & Chithambarathanu T, presented in Table 5 correspond to 4 4* transition Spectrochim Acta, 62A (2005) 918. 9 Sharma U, Kumar P & Kumar N, Mini Rev Med Chem, 10(8) from HOMO−1 to LUMO and from HOMO−2 to (2010) 678. LUMO. 10 Karthick T, Balachandran V, Perumal S, Nataraj A, J Mol Struct, 1005 (2011) 202. 4 Conclusions 11 Karthick T, Balachandran V, Perumal S &Nataraj A, Elixir In the present study, the delocalization patterns of Vib Spec, 36 (2011) 3388. charge and electron densities of atoms of NMP and 12 Glendening E D, Reed A E, Carpenter J E & Weinhold F, NBO Version 3.1, (TCI, University of Wisconsin, Madison), NBEP molecule have been explained by performing 1998. molecular orbital simulations at density functional 13 Frisch M J et al. Gaussian 03, Revision B.01, (Gaussian, Inc., B3LYP method with standard 6-311++G(d,p) basis Pittsburgh PA), 2003. set. The natural atomic orbital occupancies of both 14 Reed A E, Weinstock R B & Weinhold F, J Chem Phys, 83 NMP and NBEP are clearly describing the substituent (1985) 735. 15 Keresztury G, Holly S, Varga J, Besenyei G, Wang A V & effect in terms of difference in occupancy and energy. Durig J R, Spectrochim. Acta, 49A (1993) 2007. The natural population analysis on NMP and NBEP 16 Foster J P & Weinhold F, J Am Chem Soc, 102 (1980) 7211. thoroughly illustrates the accumulation of electrons in 17 Karabacak M, Sinha L, Prasad O, Cinar Z & Cinar M, core, valence and Rydberg sub-shell of their atomic Spectrochim. Acta Part, 93A (2012) 33. 18 Holm R H &Cotton F A, J Am Chem Soc, 80 (1958) 5658. orbitals. The natural hybrid atomic orbitals performed 19 Cotton F A & Wilkinson C W, Advanced Inorganic in this study enabling us to know about sub-shell type, Chemistry, third edition, Interscience Publisher, New York, the contribution of specified atomic electrons to 1972.