Density functional calculations on the structural and vibrational
properties of 1,4-diaminobutane
Akif Ozbay
a,*, Aysun Gozutok
baDepartment of Physics, Faculty of Science, Gazi University, Ankara, Turkey bDepartment of Physics, Faculty of Science, Selçuk University, Konya, Turkey
a r t i c l e i n f o
Article history: Received 28 May 2019 Received in revised form 20 August 2019 Accepted 21 August 2019 Available online 26 August 2019 Keywords: 1,4-Diaminobutane Infrared Raman B3LYP
a b s t r a c t
In this study, the most stable conformation of 1,4-diaminobutane molecule were determined form the previous works. The geometrical parameters and vibrational frequencies of the most stable conformation of 1,4-diaminobutane were calculated by B3LYP/6-311G(d,p) level of theory. Vibrational frequencies of 1,4-diaminobutane assignment and the Infrared and Raman intensity was determined by means of DFT. Also, the dipole moment, electronegativity, electron affinities etc. of the 1,4-diaminobutane were calculated by using DFT approximation.
© 2019 Elsevier B.V. All rights reserved.
1. Introductıon
Polyamine is a generic term for aliphatic carbohydtates con-taining at least two primary amino groups. As the name suggest, it consists of many amines. Polyamines are a basic or alkaline sub-stance since amines are similar to ammonia. Also, polyamines involve compounds with various structure, such as 1,4-diaminobutane (14DAB or Putrescine), which is an organic chemi-cal compound (C4H12N2). It is a molecule with a fundamental
car-bon chain structure. With these properties, it's used as a synthesis molecule. 14DAB is a polyamine which is organic polycation having variable hydrocarbon chains and two or more basic amino groups [1,2]. Polyamines are ornithine derivatives that form a small family of three members: 1,4- diaminobutane, spermidine and spermine [3,4]. The polyamines are presented in eukaryote cells and are necessary for cell proliferation [5e10].
14DAB is synthesized from ornithine which is formed from arginine by arginase [1,4,5,11e13]. The polyamines are widely distributed in human body and are formed in animal tissues. They are strongly basic and low molecular weight compounds which are required as a prior condition for growth. 14DAB is also formed by intestinal bacteria by decarboxylation of lysine and ornithine in the
intestine [14e16]. In addition, 14DAB has important physiological functions such as the regulation of gene expression maturation of intestine, cell growth and differentiation [17]. It was reported that 14DAB has specific role obviously in skin physiology and neuro-protection [18]. Polyamine analogues are important therapeutic agents with polyamine drug discovery and development [19e22]. Marques et al. have studied the homologous series
a
,u
-polyamines by inelastic neutron scattering spectroscopy and Raman spectros-copy with ab-initio density functional theory (DFT) methods for the calculated vibrational spectra of 1,4-diaminobutane, spermidine and spermine [23].14DAB molecules werefirst described by the German physician Ludwig Brieger in 1885 [24]. Some Raman and IR studies for the linear diamines were reported [25e29]. The current work is detailed study of the structural, some spectral analysis of 14DAB molecule. In the view of the above-mentioned facts, the structure, spectroscopic and electronic properties of 14DAB molecule were unambiguously deduced by experimental and theoretical methods. Note that the FT-IR and FT-Raman spectra of the 14DAB molecule performed the complete assignment. We have detected the FT-IR and FT-Raman spectra and evaluated computational results. Also, the DFT (B3LYP/6-311G(d,p)) calculations have been performed to study the molecular structure, spectroscopic and electronic erties for 14DAB molecule. The electronic and spectroscopic prop-erties of the studied compound have been predicted using the same level of theory.
* Corresponding author.
E-mail address:aozbay@gazi.edu.tr(A. Ozbay).
Contents lists available atScienceDirect
Journal of Molecular Structure
j o u r n a l h o m e p a g e : h t t p : / / w w w . e l se v i e r . c o m / l o c a t e / m o l s t r u c
https://doi.org/10.1016/j.molstruc.2019.126974
2. Experimental and computational details
The vibrational spectra and some electronic properties of 14DAB molecules were studied with Gaussian 09 [30] program and Gauss View 3.0 [31] graphical interface. In all calculations such as geom-etry optimization, vibrational frequency and other molecular property calculations were performed by B3LYP [32,33] functional and 6-311G(d,p) basis set. The vibrational assignments were made on the basis of the potential energy distribution (PED) calculated with scaled quantum mechanics (SQM) program [34] based on DFT calculation. Only PED components10% was evaluated to perform thefinal assignment. Additionally, the Raman activities were con-verted to Raman intensities by means of RaInt program [35]. Inaddition, frontier molecular orbital analysis, some selected elec-tronic properties and density of state analysis were performed.
The Raman spectra of the 14DAB molecule were obtained in the liquid and solid states at 240 K using a Jobin Yvon model Hg2S
double monochromator. The Raman spectra were excited using the 5145 A and 4880A lines from a Spectra-Physics model 164e06 argon ion laser. The spectral slit width was 3 cm1for the liquids and 2 cm1 for the solids. The IR spectra were recorded with a PerkinElmer model 521 grating spectrometer. The liquids were analysed between CsI windows in the 4000-250 cm1range with a slit program which gives a resolution of 1.5 cm1at 1000 cm-l. The solids were obtained by gradually lowering the temperature of liquidfilms placed between CsI windows in glass cryostats of a conventional type.
3. Molecular geometry
14DAB is considered the smallest biogenic polyamines. In the present work, the conformational search was based on the results from previous studies on the smaller amines. 14DAB molecule can adopt different conformations, which may be characterized in terms of the skeletal dihedral angles near to 60 (Gauche, G) 180 (Trans, T) and 60 (Gausche0, G0). The conformations of 14DAB
molecule has the little different energies [36]. As in the previous works [37e39], only the geometries with all skeletal dihedral an-gles equal to 180(all-trans) were considered in the present work. Molecular structure and atomic numbering were presented inFig. 1. The calculated structural parameters with the X-Ray data for optimized structure were provided inTable 1. The calculated data were compared with determined X-Ray data of 14DAB molecule and Putrescine dihydrochloride [40,41].
4. Vibrational assignment
The spectral assignments have been performed on the recorded
FT-IR and FT-Raman spectra based on the theoretically predicted wavenumbers by density functional B3LYP/6- 311G(d,p) method collected inTable 2. The FT-IR and FT-Raman spectra of 14DAB were taken from Ref. [42]. None of the predicted frequencies is imagi-nary, implying that the optimized geometry is located at the local minimum point on the potential energy surface. It is known that DFT potentials systematically overestimate the vibrational wave-numbers. These discrepancies are corrected either by computing anharmonic corrections explicitly or by introducing a scaled force field [43] or directly scaling the calculated wavenumbers with the proper factor [44]. The scaling factor of 0.9668 is used for B3LYP method. 14DAB molecule has 18 atoms in which the C and N atoms are planar and the H atoms are out of plane. 14DAB molecule be-longs to the point group C2h. For an N-atomic molecule the three
cartesian displacements of the N-atoms provide 3 N inner modes. Since the 14DAB molecule is a non-linear molecule, there are 3Ne6 ¼ 48 vibration modes. It has 11 AU modes, 13 BU modes, 14 AG modes and 10 BG modes. All AU and BU fundamental vibrations are active in IR spectra, while all AG and BG modes are active in Raman spectra. Comparison of the frequencies calculated at DFT method using 6-311G(d,p) basis set with experimental values re-veals that the B3LYP method show very good agreement with experimental observation due to inclusion of electron correlation for this method. Vibrational frequencies of 1,3-diaminopropane [45], a molecule closely related to 14DAB, compared to the those of 14DAB inTable 2.
According to Socrates [46,47] the frequencies of amino group appear around 3500e3300 cm1for NH2stretching. The harmonic
asymmetric and symmetric stretching modes of NH2group were
measured at 3335 cm1(BG mode, Raman spectra), 3332 cm1(AU mode, Infrared spectra), 3170 cm1(BU mode, Infrared spectra) and 3170 cm1(AG mode, Raman spectra),respectively. The predicted bands at 3433 cm1, 3433 cm1, 3362 cm1 and 3362 cm1 are ascribed to asymmetric and symmetric NH2stretching respectively.
Bellamy and Williams [48] and Mansy et al. [49] suggested that the NH2scissoring mode lie in the region 1590-1650 cm1. In
accor-dance with their conclusion, the NH2scissoring mode is identified
with a weak band at 1623 cm1(AG mode, Raman spectra) and 1606 cm1 (BU mode, Infrared spectra) in FT-IR and FT-Raman, respectively. The computed
d
NH2 scissoring vibrations at1611 cm1(mode no: 35) and 1612 cm1 (mode no: 36) is in agreement with the recorded spectral data. The observed bands 1307 cm1(AU mode, IR spectra) and 1347 cm1(BG mode, Raman spectra) were attributed to the twisting mode of the NH2group.
The theoretically scaled NH2twisting vibrations at 1345 cm1and
1346 cm1 exactly correlates with experimental observations [50e56].
The asymmetric CH2 stretching vibration, generally, was
observed in the region 3000e2900 cm1, while the CH2symmetric
stretch will appear between 2900 cm1and 2800 cm1[50e56]. In the present study, the bands occurring at 2926 cm1(BU mode, Infrared spectra), 2914 cm1 (AU mode, Infrared spectra) and 2910 cm1(BG mode, Raman spectra) are assigned to asymmetric CH2stretching modes. Observed symmetric CH2stretching modes
of 14DAB were measured at 2860 cm1(BU mode, Infrared spectra) and 2858 cm1(AG mode, Raman spectra).
In the present assignment, the CH2 bending modes follow in
decreasing wave number order, the order is: CH2scissoring> CH2
wagging> CH2 twisting> CH2 rocking. Since the bending modes
involving hydrogen atom attached to the central carbon fall into the 1450e875 cm1range. The fundamental CH2vibrations are able to
show scissoring, wagging, twisting and rocking modes and pres-ently appear in the expected frequency regions 1500e800 cm1
[50e56]. In FT-IR spectrum of 14DAB, at 1469 cm1and 1457 cm1 in the Infrared spectra were assigned to CH2scissoring vibrations.
These vibrations were predicted at 1461 cm1 and 1436 cm1by using DFT calculation. In the Raman spectra, the same vibrations of 14DAB molecule were detected at 1450 cm1 and 1439 cm1 by Giorgini et al. [42]. In our calculation, these peaks were predicted at 1434 cm1 and 1450 cm1by DFT. In the present work, the CH2
wagging mode was measured in the range 1287 cm1(BG mode, Raman spectra), 1379 cm1 (BU mode, Infrared spectra), corre-sponding to CH2calculated to be in the range 1285 cm1, 1347 cm1,
respectively. The present assignments are agree well with the values available in literature [50e56]. In the present work, the frequencies observed at 1104 cm1(IR), 1087 cm1(IR), 1060 cm1 (IR), 1054 cm1 (Raman) and 1109 cm1 (Raman) have been assigned to CH2 twisting vibrations. The theoretically computed
values in the range 1027e1082 cm1 shows excellent agreement
with experimental data by B3LYP/6-31G(d,p) method. The CH2
rocking vibrations calculated to be 712 cm1is also in agreement with recorded value of 762 cm1(IR, AU mode).
5. Molecular electrostatic potential (MEP)
Electrostatic potential maps are very useful three-dimensional diagram for the investigation of the molecular structure with its physiochemical property relationships [57e61]. The MEP diagrams is used to visualize the charge distributions and charge related properties. Total electron density surface mapped and MEP
predicted by DFT (B3LYP/6-311G(d,p)) method are given inFig. 2for 14DAB molecule. In the color scheme for the MEP surface, red color region is electron rich or partially negative charge. Blue color region has the electron deficient or partially positive charge. Light blue region have slightly electron deficient region. Yellow color region has lightly electron rich region. In the MEP of 14DAB molecule, nitrogen atoms have the electron rich centers.
6. Density of state (DOS)
In the boundary region, neighbor orbitals can show quasi-degenerate energy levels. In similar cases, the consideration of only the HOMO and LUMO may not yield a realistic description of the frontier orbitals. Therefore, the DOS is predicted and formed by using the Gauss-Sum2.2 software. The information of molecular orbital is transformed by using the Gaussian curves of unit height and full width at half maximum (FWHM) of 0.3 eV. In present work, the DOS plot of 14DAB molecules was shown inFig. 3. It provides a pictorial representation of molecule orbital compositions and their contributions to chemical bonding [62e64].
7. HOMO-LUMO analysis
By using HOMO and LUMO energy values for a molecule, the global chemical reactivity descriptors of molecules such as
Table 1
Optimized geometric parameters of 14DAB molecule.
Bond Lengths (Å) DFT X-Raya X-Rayb Bond Angles (º) DFT X-Raya X-Rayb Dihedral Angles (º) DFT X-Raya X-Rayb
C 1 C 2 1.536 1.524 1515 C2C1eH3 108.8 109.7 114,2 H3C1eC2eH5 64.56 62.22 58,63 C 1 H 3 1.098 1.015 0,940 C2C1eH4 108.8 109.2 108,2 H3C1eC2eH6 179.8 179.1 179,0 C 1 H 4 1.098 0.962 0,880 C2C1eC9 113.6 113.0 111,0 H3C1eC2eN18 57.63 58.85 63,92 C 1 C 9 1.533 1.522 1503 H3C1eH4 106.1 106.6 110,1 H4C1eC2eH5 179.8 178.7 178,2 C 2 H 5 1.095 0.970 0,907 H3C1eC9 109.5 108.5 102,3 H4C1eC2eH6 64.56 64.32 55,91 C 2 H 6 1.095 0.993 0,694 H4C1eC9 109.5 109.4 110,7 H4C1eC2eN18 57.63 57.71 59,16 C 2 N18 1.465 1.463 1483 C 1 C2eH 5 109.3 109.7 112,8 C9C1eC2eH5 57.80 59.11 56,56 H 7 N 18 1.016 0.870 0,774 C1C2eH6 109.3 108.5 113,6 C9C1eC2eH6 57.80 57.78 65,82 H 8 N 18 1.016 0.919 0,935 C1C2eN18 116.2 115.5 111,2 C9C1eC2eN18 180.0 179.8 157,9 C 9 C 10 1.536 1.524 1515 H5C2eH6 105.9 107.5 107,0 C2C1eC9eC10 180.0 180.0 180,0 C 9 H 11 1.098 0.962 0,940 H5C2eN18 107.7 107.3 102,5 C2C1eC9eH11 58.01 58.01 59,76 C 9 H 12 1.098 1.015 0,880 H6C2eN18 107.7 108.4 108,7 C2C1eC9eH12 58.01 57.95 57,61 C 10 H13 1.095 0.993 0,907 C 1 C9eC 10 113.6 113.0 111,0 H3C1eC9eC10 58.01 57.95 57,61 C 10 H 14 1.095 0.970 0,694 C1C9eH11 109.5 109.4 110,7 H3C1eC9eH11 63.96 64.05 77,69 C 10 N 17 1.465 1.463 1483 C1C9eH12 109.5 108.5 102,3 H3C1eC9eH12 180.0 180.0 180,0 H 15 N 17 1.016 0.919 0,774 C10C9eH11 108.8 109.2 108,2 H4C1eC9eC10 58.01 58.01 62,63 H 16 N 17 1.016 0.870 0,935 C10C9eH12 108.8 109.7 114,2 H4C1eC9eH11 180.0 180.0 180,0 H 11 C 9eH12 106.1 106.6 110,1 H4C1eC9eH12 63.96 64.05 62,63 C 9 C 10eH13 109.3 108.5 112,8 C1C2eN18eH7 58.33 58.27 58,42 C 9 C10eH 14 109.3 109.1 113,6 C1C2eN18eH8 58.33 57.13 61,15 C 9 C 10eN17 116.2 115.5 111,2 H5C2eN18eH7 178.6 179.6 176,6 H 13 C 10eH14 105.9 107.5 107,2 H5C2eN18eH8 64.73 64.93 63,76 H 13 C 10eN17 107.7 108.4 108,7 H6C2eN18eH7 64.73 63.78 63,36 H 14 C 10eN17 107.7 107.3 102,5 H6C2eN18eH8 178.6 179.1 177,0 C 10 N 17eH15 110.0 107.5 101,8 C1C9eC10eH13 57.80 57.78 65,82 C 10 N 17eH16 110.0 107.7 114,2 C1C9eC10eH14 57.80 59.11 56,56 H 15 N 17eH16 106.1 106.4 110,8 C1C9eC10eN17 180.0 179.8 179,11 C 2 N 18eH7 110.0 109.7 101,8 H11C9eC10eH13 64.56 64.32 55,91 C 2 N 18eH8 110.0 107.5 114,2 H11C9eC10eH14 179.8 178.7 178,2 H 7 N 18eH8 106.1 106.4 110,8 H11C9eC10eN17 57.63 57.71 59,16 H 12 C 9eC10eH13 179.8 179.1 179,0 H 12 C 9eC10eH14 64.56 62.22 58,63 H 12 C 9eC10eN17 57.63 58.85 63,92 C 9 C 10eN17eH15 58.33 57.13 61,15 C 9 C 10eN17eH16 58.33 58.33 58,42 H 13 C 10eN17eH15 178.6 179.1 177,0 H 13 C 10eN17eH16 64.73 63.78 63,36 H 14 C 10eN17eH15 64.73 64.93 63,76 H 14 C 10eN17eH16 178.6 179.6 176,6 aTaken from Ref. [40].
chemical hardness (
h
), chemical potential (m
), softness (S), elec-tronegativity(c
)and electrophilicity index(u
)were defined. On the basis of EHOMOand ELUMO, they are calculated using below equations.Using Koopman's theorem for closed shell molecules [65e68],
I ¼ EHOMOðIonization potentialÞ A ¼ ELUMOðElectron AffinityÞ
The hardness of the molecule is
h
¼I A 2The chemical potential of the molecule is
m
¼ I A 2The electronegativity of the molecule is
c
¼I þ A 2The electrophilicity index of the molecule is
u
¼m
22h
The hard molecules have a large HOMO-LUMO gap, whereas soft molecules have a small HOMO-LUMO gap. In terms of chemical
Table 2
Calculated and observed vibrational wavenumbers (cm1) and Potential Energy Distributions (PED) of 14DAB molecule.
Theoretical Experimental TEDc
Freqa
Ib
IR IbRaman IR Raman IR/Raman d n 1 AU 73 0.196 0.000 89 e tHCCH(38)þtCCCH(30) n 2 AU 93 2.479 0.000 100 e tHCCH(40)þtCCCH(31) n 6 AU 291 23.64 0.000 301 e tCCNH(26)þtCCCH(12) n 10 AU 712 0.773 0.000 761 e 769 dHCH(48)þdCCH(14)þtCCCH(14) n 14 AU 853 0.206 0.000 e 875 dCCH(18)þtCCCH(14)þtHCCH(10) n 19 AU 1042 0.045 0.000 1087 e 1095 d(30)þHCHdCCH(28)þdCNH(11)þtCCCH(11) n 24 AU 1273 0.050 0.000 1302 e 1317 dCCH(32)þtHCCH(25)þtCCCH(12) n 27 AU 1345 0.467 0.000 1307 e 1353 dCNH(25)þdCCH(24)þtHCCH(15) n 42 AU 2926 1.741 0.000 2914 e 2926 nCH(70)þtCCCH(10) n 44 AU 2959 38.96 0.000 e nCH(75)þtHCCH(11) n 47 AU 3433 0.119 0.000 3332 e 3359 nNH(78) n 3 BU 126 1.406 0.000 116 e dCCH(22)þtHCCH(20)þtCCCH(12) n 9 BU 487 2.827 0.000 e 463 dHCH(15)þd(14)þCCH dCCN(12)þtCCCH(10)þdCCC(10) n 12 BU 829 100 0.000 e tCCNH(19)þdCNH(18)þdHNH(10) n 15 BU 966 28.74 0.000 954 e nCC(14)þdCCH(12)þtCCNH(12)þdCNH(10)þtHCCH(10) n 20 BU 1054 4.440 0.000 1060 e 1068 d(26)þHCHnCN(17)þdCNH(10)þtCCCH(10) n 23 BU 1223 1.295 0.000 1104 e dCCH(23)þdHCH(34)þtCCCH(12) n 29 BU 1347 6.720 0.000 1379 e 1389 dCCH(30)þtHCCH(15)þtCCCH(10) n 32 BU 1436 0.167 0.000 1457 e 1435 dHCH(24)þtCCCH(16)þdCCH(10) n 34 BU 1461 0.930 0.000 1469 e 1471 dHCH(25)þtCCCH(17)þdCCH(12) n 35 BU 1611 12.66 0.000 1606 e 1601 dHNH(22)þdCNH(17)þtCCNH(16) n 38 BU 2896 8.262 0.000 2860 e 2855 nCH(82) n 41 BU 2920 35.10 0.000 2926 e nCH(80) n 45 BU 3362 0.786 0.000 3170 e 3190 nNH(92) n 7 AG 315 0.000 100.0 e 276 d(15)þCCN dCCH(14)þtHCCH(13)þtCCCH(10) n 8 AG 338 0.000 59.69 e 373 dCCH(22)þtHCCH(20)þdCCC(16)þnCC(11)þtCCCH(10) n 13 AG 840 0.000 11.44 e 892 910 tCCNH(18)þdCNH(17)þdHNH(10) n 17 AG 998 0.000 4.150 e 969 976 nCC(32)þdCCH(13)þnCN(12)þdCCC(10)þtHCCH(10) n 18 AG 1027 0.000 27.90 e 1054 1070 d(22)þHCHnCC(10)þnCN(15)þdCCH(10) n 21 AG 1082 0.000 13.25 e 1109 1095 dHCH(15)þd(12)þCCH nCN(11)þdCCC(11)þdCNH(11)þnCC(10) n 26 AG 1307 0.000 3.222 e dCCH(30)þtHCCH(17)þtCCCH(13) n 30 AG 1348 0.000 1.377 e 1368 1390 dCCH(33)þtHCCH(16)þtCCCH(10) n 31 AG 1434 0.000 55.75 e 1439 1441 dHCH(34)þtCCCH(15)þdCCH(10) n 33 AG 1450 0.000 11.87 e 1450 1472 dHCH(28)þtCCCH(16)þdCCH(10) n 36 AG 1612 0.000 16.71 e 1623 1603 dHNH(22)þdCNH(17)þdCNH(16) n 37 AG 2892 0.000 74.21 e 2858 2858 nCH(77)þtHCCH(10) n 40 AG 2917 0.000 74.39 e 3170 3190 nCH(76) n 46 AG 3362 0.000 48.22 e 3302 nNH(92) n 4 BG 154 0.000 0.118 e 173 tCCCH(60)þtCCCN(11) n 5 BG 284 0.000 54.72 e 276 tCCCN(30)þtCCCH(10) n 11 BG 746 0.000 0.117 e 770 tHCCH(30)þtCCCH(18)þdCCH(14) n 16 BG 979 0.000 2.518 e tCCCH(34)þdCCH(13)þdCNH(13)þtHCCH(10) n 22 BG 1211 0.000 0.262 e dCCH(21)þtCCCH(20)þtHCCH(15) n 25 BG 1285 0.000 37.28 e 1287 1297 dCCH(43)þtHCCH(19)þtCCCH(10) n 28 BG 1346 0.000 21.39 e 1347 1357 dHNH(28)þdHCH(21)þtHCCH(16) n 39 BG 2911 0.000 70.02 e 2910 2900 nCH(64)þtCCCH(14) n 43 BG 2952 0.000 25.64 e 2930 nCH(70)þtHCCH(10) n 48 BG 3433 0.000 25.11 e 3335 3363 nNH(77)
n; stretching;d; in-plane bending;g; out-of-plane bending;t; torsion.
bRelative absorption intensities and Raman intensities normalized with highest peak absorption equal to 100. aObtained from the wavenumbers calculated at B3LYP/6-311G(d,p) using scaling factors 0.9668.
c Total energy distribution calculated at B3LYP/6-311G(d,p) level of theory. Only contributions10% are listed. d Taken form ref [45].
reactivity, we can conclude that soft molecules will be more reac-tive than hard molecules for unimolecular reactions such as isomerization and dissociation. In the present study,
D
EHL gapvalue is predicted at7.246 eVinFig. 4. In addition, it can be stated that 14DAB molecule is more polarizable than the urea because their energy gap are lower than the urea (
D
EHL¼6.7063 eV). Thechemical hardness is also a good indicator of chemical stability. As seen in Table 3, the chemical hardness, chemical potential and electronegativity of 14DAB molecule were determined at 3.623 eV, 2.598 eV and 2.598 eV, respectively.
The energy of HOMO is directly related to the ionization po-tential (IP) and LUMO energy is directly related to the electron af-finity (EA). The IP energy value of 6.221 eV is required to remove an electron from the HOMO. The energy values of EA (1.025 eV for 14DAB) indicate that the studied molecules readily accept electrons to form bonds. The biological activity can be described using the electrophilicity index. For 14DAB molecule, the electrophilicity in-dex was predicted at 0.931 eV [65e68].
8. Fukui function
The condensed Fukui function is used as a descriptor in quan-titative structure-activity relationships. Our calculations show that the condensed Fukui function can give valuable information about the site selectivity in chemical. In particular, it has been shown that the selectivity towards protonation in the molecule can be correctly evaluated by the electrophilic. Fukui function described in this paper [69e73].
fþk ¼ qkðN þ 1Þ qkðNÞ for nucleophilic attack Fig. 2. Molecular electrostatic potential and electron density maps of 14DAB molecule.
Fig. 3. Density state of 14DAB molecule.
fk ¼ qkðNÞ qkðN 1Þ for electrophilic attack f0k¼ 1 2 ½qkðN þ 1Þ qkðN 1Þfor neutralðradicalÞattack
In these equations, qk is the atomic charge at the rth atomic site is the neutral (N), anionic (Nþ1), cationic (N-1) chemical species. Roy et al. [72]. introduced the relative electrophilic attack as the highest value of the fþkfk
!
ratio and relative nucleophilic attack the highest value of the fkfþ
k
!
ratio. The maximum value of the electrophilic reactivity descriptors was determined at H3, H4, H11
and H12atoms. These hydrogen atoms connected the central carbon
atoms (C1and C9atoms). H5, H6, H13and H14atoms connected to
the C2and C10atoms. As seen inTable 4, the electrophilic reactivity
of the H5, H6, H13and H14atoms smaller than those of the H3, H4,
H11and H12atoms. The H7, H8, H15and H16atoms connected the
nitrogen atoms. Among all hydrogen atoms, these atoms have the lowest electrophilic reactivity. The maximum value of the nucleo-philic reactivity descriptors at atoms was predicted at N17and N18
atoms. The around hydrogen atoms, nitrogen atoms site are prone to electrophilic attack, nucleophilic attack respectively. From the
values gathered inTable 4, the fþkf k
!
ratio in 14DAB molecule predicted the bigger than fkfþ
k
!
ratio for (H3, H4, H5, H6, H7, H8,
H11, H12, H13, H14, H15, H16, C1and C2) and nucleophilic (N17, N18, C9
and C10.) attack during reaction depends on the local behavior of
molecule [69e73]. 9. Conclusions
In conclusion, we report the experimental (FT-IR and FT-Raman spectra) and theoretical wave number and their intensity, total energy distributions, some electronic properties such as EHOMO,
ELUMO, electron affinity, ionization potential, global hardness,
soft-ness, chemical potential, electronegativity and electrophilicity for 14DAB molecule. The molecular geometry and vibrational fre-quencies of the 14DAB molecule were predicted and compared with the experimental results. Comparison to theoretical results from the DFT calculations shows that the results such as vibrational frequencies agree well with the experimental data.
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Table 3
Some selected electronic properties value of 14DAB in its ground state.
EHOMO(eV) 6.221 DEGAP(eV) 7.246 ELUMO(eV) 1.025 E HOMO-1(eV) 6.725s DEGAP1(eV) 7.823 E LUMOþ1(eV) 1.098 E HOMO-2(eV) 9.007 DEGAP2(eV) 10.622 E LUMOþ2(eV) 1.616 IP (eV) 6.221 EA (eV) 1.025 h(eV) 3.623 c(eV) 2.598 m 2.598 u 0.931 Table 4
Condensed Fukui functions calculated from Hirshfeld charges.
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