Theoretical Study of the Chemical Reactivity of Five Schiff Bases Derived From Dapsone by the DFT Method

_____________________________________________________________________________________________________

*Corresponding author: E-mail: [email protected];

22(4): 1-11, 2018; Article no.CSIJ.41427

ISSN: 2456-706X

(Past name: American Chemical Science Journal, Past ISSN: 2249-0205)

Theoretical Study of the Chemical Reactivity of Five

Schiff Bases Derived From Dapsone by the DFT

Method

Jean Stéphane N’dri

, Mamadou Guy-Richard Koné

,

Charles Guillaume Kodjo

,

Ahmont Landry Claude kablan

, Sopi Thomas Affi

,

Lamoussa Ouattara

and Nahossé Ziao

1

Laboratoire de Thermodynamique et de Physico-Chimie du Milieu, UFR SFA, Université Nangui Abrogoua, 02 BP 801 Abidjan 02, Côte-d’Ivoire.

2_{Laboratoire de Chimie BioOrganique et de Substances Naturelles, Université Nangui Abrogoua,}

UFR-SFA, 02 B.P. 801 Abidjan 02, Côte-d’Ivoire.

3

UFR des Sciences Biologiques, Université Péléforo Gon Coulibaly de Korhogo, BP 1328 Korhogo, Côte d’Ivoire.

Authors’ contributions

This work was carried out in collaboration between all authors. Authors JSN and MGRK designed the study, performed the statistical analysis, wrote the protocol and first draft of the manuscript. Authors CGK and NZ managed the analyses of the study. Authors ALCK, STA and LO managed the literature searches. All authors read and approved the final manuscript.

Article Information

DOI: 10.9734/CSJI/2018/41427

Editor(s):

(1)Gustaaf Schoukens, Professor, Department of Textiles, Ghent University, Belgium.

Reviewers:

(1)Ahmed Mohammed Abu-Dief Mohammed, Sohag University, Egypt. (2)Sema Salgin, Cumhuriyet University, Turkey. (3)Daniel Glossman-Mitnik, CIMAV, Mexico. Complete Peer review History:http://www.sciencedomain.org/review-history/24546

Received 19th February 2018 Accepted 30th April 2018

Published 9th May 2018

ABSTRACT

This theoretical study of chemical reactivity was conducted using the method of the Density Functional Theory (DFT), with B3LYP/6-311G (d, p) as calculation level. A series of five (05) Schiff bases derived from 4.4 '-diaminodiphenylsulfone (Dapsone) was concerned and allowed to predict the chemical reactivity of these compounds. Molecular geometries and electronic properties such as the energies of the frontier molecular orbitals (HOMO and LUMO), ionization potential (I), and

electron affinity (A) were examined to obtain a better overview of the molecular properties. Thus compound 4, whose energy gap between the frontier orbitals (HOMO and LUMO) is ΔEgap = 3.910 eV appears to be the most polarizable. It is the most reactive with the lowest kinetic stability compared to all the studied molecules. The values of the global reactivity descriptors confirmed the great chemical reactivity of the compound 4. Local indices of reactivity and dual descriptors were calculated to indicate the probable sites of Electrophilic and nucleophilic attacks of the various studied compounds.

Keywords: Chemical reactivity; global descriptors; local descriptors; dual descriptors.

1. INTRODUCTION

The fight against infectious diseases remains a challenge of public health essential; this is explained by the high mortality and morbidity rate linked to these diseases [1,2]. Also, the anti-infectious chemotherapies are now losing

efficacy because of drug-resistance’s

phenomenon of infectious germs [3]. Nowadays Dapsone presents many undesirable effects such as cutaneous, neurological and psychiatric infections. It shows resistances during treatment too [4]. In such context, the continuation of the development of new effective drugs becomes a real necessity. Several researchers have recently set up Schiff bases and azetidinones derived from Dapsone [5-7]. In addition, the Quantitative Structure-activity Relationship (QSAR) [8, 9] studies of this series were made in order to understand well their chemical reactivity. With the development of computational techniques and computational chemistry, quantum chemistry provides an overview of the electronic structures

of molecules and strongly propels the

development of the traditionally experimental chemistry [10]. Currently, the DFT method has been accepted as a popular approach for

calculating the structural characteristics and energies of molecules by the scientific community [11-14] and for the efficacy and

accuracy of evaluating a number of molecular properties [15]. Parr and Yang

followed the idea that well-known chemical properties such as electro-negativity, chemical potentials and affinities could be accurately described and computed by manipulating electron density as the fundamental quantity [16, 17]. On the other hand, from the work of Fukui and its theory of Frontier molecular orbitals (FMO) [18], The same authors have generalized

the concept and proposed the function of Fukui as a tool for describing local reactivity in molecules [19,20]. The present study focuses on five (05) Schiff bases derived from

Dapsone that are shown in Fig. 1.

These Schiff bases are obtained by

condensation of Dapsone with benzaldehydes

diversely substituted in ethanol in the presence of the concentrated hydrochloric acid

as a catalyst, were synthesized and tested by S. J. Wadher et al. [7] for their antibacterial and antifungal activities. These molecules presented millimeters. The purpose of this work is to

Compound 1

Fig. 1. Molecular structures and numbering of Schiff’s atoms bases derived from Dapsone

determine theoretically the privileged sites of electrophilic and nucleophilic attacks on the aromatic carbon atoms contained in these Schiff bases, by different quantum methods.

2. MATERIALS AND METHODS

2.1Level of Calculation

The theoretical study of chemical reactivity was conducted on the basis of three theoretical approaches. The first concerns the analysis of surfaces of Molecular Electrostatic Potential (MEP).The second approach is relative to the Frontier Molecular Orbitals (FMO). The latest approach focuses on local indices of reactivity as well as dual descriptors. The geometries of the molecules have been optimized at the DFT calculation level with the functional B3LYP [21,22] in the base 6-311 G (d, p) using the software Gaussian 09 [23]. This hybrid function gives better energies and is in good agreement with ab initio high-level methods [24,25]. Concerning split-Valence and Triple-zeta (6-311G (d, p)) base, it is sufficiently extended and the taking into account of polarization functions

are is important for the explanation of the pairs of electrons of heteroatoms those are not involved in a bound. The geometries are (kept) maintained constant for cationic and anionic systems. Global reactivity indices were obtained from the conceptual DFT model [16]. The

Hierarchical Cluster Analysis (HCA) was

conducted using XLSTAT software [26]. For chemical reactivity indices, they were determined by using electronic populations calculated with the Mulliken Population Analysis (MPA) [27].

2.2 Reactivity Descriptors

2.2.1 Global Descriptors

To predict chemical reactivity, some theoretical descriptors related to the conceptual DFT have been determined. In particular, the Lowest Unoccupied (vacant) Molecular Orbital (LUMO) energy (ELUMO), the Highest Occupied Molecular

Orbital (HOMO) energy (EHOMO), the

electronegativity (χ), the global softness (σ), and the global electrophilicity Index (ω). These descriptors are all determined from the optimized molecules. It should be noted that, the Compound 3

Compound 4

descriptors linked to the frontier molecular orbitals have been calculated in a very simple

way according to the approximation of

Koopmans [28].The LUMO energy characterizes the sensitivity of the molecule to nucleophilic

attack, and concerning HOMO’s one, it

characterizes the susceptibility of a molecule to an electrophilic attack. The electronegativity (χ) is the parameter that translates the ability of a molecule not to let its electrons escape. The global softness (σ) expresses the resistance of a system to the change in its number of electrons. The global electrophilicity index characterizes the electrophilic power of the molecule. These different parameters are calculated from the following equations (1):

= − = −

= − = − 1 2⁄ ( + )

= ( − ) 2⁄ (1)

= 2 = 1⁄

2.2.2 Local descriptors and dual descriptors

In order to differentiate the reactive behaviors of atoms forming a molecule, different indices were used. These are precisely local indices and dual descriptors of reactivity. Local reactivity descriptors, such as function of Fukui [29]

( , ) , local softness ( , ) , local

electrophilic power ( , ), and dual descriptors were proposed to explain the selectivity of electrophilic and nucleophilic attacks of the molecule. It should be recalled (remembered) that the function of Fukui expresses reactivity when the molecule is attacked by a nucleophilic

reagent, whereas the function of

Fukui provides information about the

electrophilic attack on a given site. The value of the highest Fukui function is assigned to the most active site. The condensed indices and express the ability of a site to receive electron density by nucleophilic attack, in

contrast, the and indices express the

ability of a site to yield electron density by electrophilic attack. With regard to the dual descriptor, it is a good tool to predict reactivity and to understand the problem of regioselectivity. Indeed, a dual positive descriptor corresponds to a site which is able to receive electron density, in other words, it is the most electrophilic.

Conversely, a dual negative descriptor

corresponds to a site which is capable to yield

electron density, so it is the most nucleophilic. A site with a value of the dual descriptor close to zero corresponds to a site whose capacity to receive and to yield electron density are equivalent. The different values of the local descriptors are calculated from the equations (2) below [30-33]:

= ( + 1) − ( )

= ( ) − ( − 1)

=

= (2) =

=

Where: _{( )}: Electron population of the atom k in the neutral molecule

( + 1): Electron population of the atom k in the anionic molecule.

( − 1): Electron population of the atom k in the anionic molecule.

The values of the dual descriptors [33-36] are obtained from the equations (3):

∆ = −

∆ = − (3)

∆ = −

3. RESULTS AND DISCUSSION

3.1 Molecular Electrostatic Potentials (MEP)

The surfaces of the electrostatic potentials of studied molecules were drawn after optimization at the level B3LYP/ 6-311G (d,p). They are shown in Fig. 2.These surfaces are associated with a color code which is moving continuously from red indicating the most negative potentials to blue indicating the most positive potentials [37] passing through orange, yellow and green [38].

These maps indicate, on the one hand, that the heteroatoms (S, O, N, Cl et F) are the sites of electrophilic attacks because they have a red proximity area of negative potential with a high electron concentration around the (-SO2-) bond of the Dapsone nucleus. On the other hand, the carbon atoms, except those involved in the

azomethine binding (-CH=N-), are more

Fig. 2. Surfaces of Molecular Electrostatic Potentials of Schiff bases derived from Dapsone

3.2 Analysis of Frontier Molecular Orbitals

The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) called frontier orbitals and they play a fundamental role in the qualitative interpretation of chemical reactivity [39]. The highest occupied molecular orbital (HOMO), which can be considered as the external orbital containing electron, tends to give these electrons as an electron donor. On the other hand, the lowest

unoccupied molecular orbital (LUMO) is

perceived as the lowest orbital containing free places so able to accept electrons [40]. Therefore, while the energy of HOMO is directly related to the ionization potential, that of LUMO is directly related to electron affinity. The energy difference between HOMO and LUMO called Energy Gap, is an important stability factor for the structures [41]. The HOMO-LUMO energy gap helps to characterize the chemical reactivity

and kinetic stability of the molecule [42]. A molecule with a high energy gap (ΔEgap) is less

polarizable and is generally associated with low chemical reactivity and high kinetic stability

[43]. Fig. 3 below represents the molecular orbital of HOMO and LUMO of Dapsone derivatives obtained using the method B3LYP/6-311 G(d,p).

The energetic parameters of the frontier orbitals are gathered in Table 1.

These results show that compound 4 has the smallest energy gap (ΔEgap = 3.910 eV). So it is the most polarizable and possess the highest chemical reactivity and the lowest kinetic stability among all the studied molecules. On the other hand, compound 3 has the greatest value of the energy gap which is 4.154 eV. Thus, molecule 3 is the least polarizable, with low chemical reactivity and high kinetic stability among the five (05) studied molecules.

Table 1. Energetic descriptors of the studied compounds

Compounds EHOMO(eV) ELUMO(eV) ΔEgap (eV) I (eV) A (eV)

1 -6.438 -2,380 4.058 6.438 2.380

2 -6.573 -2.492 4.081 6.573 2.492

3 -6.500 -2.346 4.154 6.500 2.346

4 -6.671 -2.761 3.910 6.671 2.761

5 -6.083 -2.018 4.066 6.083 2.018

3.3 Hierarchical Cluster Analysis (HCA)

Fig. 4. shows the HCA of the studied molecules. The horizontal lines represent the compounds. The vertical lines the similarity values between pairs of compounds, a compound and a group of compounds and among groups of compounds.

We can note from this analysis that the studied compounds were grouped into three categories: the most active compounds are 2 and 4, compound 3, moderately active and less active compounds 1 and 5.

3.4 Reactivity Descriptors

3.4.1 Global reactivity descriptors

The study of the global reactivity of molecules is based on the calculation of the global indices inferred from the electronic properties. The global indices of the reactivity of the studied Schiff bases were calculated from the equations (1) and recorded in Table 2.

The chemical hardness (softness) value of compound 4 (η = 1.955 eV) is the lowest among studied molecules. Thus, it appears that

compound 4 is more reactive than all the studied compounds. Also, we note that compound 4 has its value of electronegativity (χ = 4.716 eV) which is higher than other compounds' value so it is the best electron acceptor. In addition, the electrophilic index value of compound 4 (ω = 5.688 eV) indicates that it is the most electrophilic one.

3.4.2 Local and dual reactivity descriptors

Local indices and dual descriptors of reactivity were also determined for each molecule according to equations (2). The concerned sites are the carbon atoms linked to a hydrogen atom in the different aromatic nuclei of each molecule. These different indices and descriptors of reactivity are grouped in Tables 3-7.

The values of the local and dual descriptors of compound 1 calculated at the level B3LYP/ 6 311G(d,p), show that the carbon atoms C9 and C19with the value Δω = -0.070, are the preferred sites of electrophilic attack. According to this same level of calculation, a nucleophilic attack will take place preferentially on the C35 and C46 atoms.

Table 2. Global descriptors for chemical reactivity of Schiff bases 1-5

Compounds μ (eV) χ (eV) η (eV) σ (eV) ω (eV)

1 -4.409 4.409 2.029 0.493 4.790

2 -4.532 4.532 2.040 0.490 5.034

3 -4.423 4.423 2.077 0.481 4.709

4 -4.716 4.716 1.955 0.511 5.688

5 -4.050 4.050 2.033 0.492 4.035

Table 3. Reactivity descriptors of compound 1 computed using Mulliken population analysis (MPA)

Sites Local descriptors Dual descriptors

f- f+ σ- σ+ η- η+ ω- ω+ Δf Δσ Δω

C5 0.008 0.011 0.004 0.005 0.017 0.022 0.039 0.051 0.002 0.001 0.012

C6 0.010 0.012 0.005 0.006 0.020 0.024 0.047 0.057 0.002 0.001 0.010

C7 0.021 0.024 0.010 0.012 0.042 0.048 0.099 0.114 0.003 0.001 0.014

C9 0.033 0.019 0.016 0.009 0.068 0.038 0.160 0.090 -0.015 -0.007 -0.070

C15 0.008 0.011 0.004 0.005 0.017 0.022 0.039 0.051 0.002 0.001 0.011

C16 0.010 0.012 0.005 0.006 0.020 0.024 0.047 0.058 0.002 0.001 0.011

C17 0.021 0.024 0.010 0.012 0.042 0.048 0.099 0.114 0.003 0.001 0.014

C19 0.033 0.019 0.016 0.009 0.068 0.038 0.160 0.090 -0.015 -0.007 -0.070

C30 0.018 0.021 0.009 0.010 0.036 0.043 0.086 0.101 0.003 0.002 0.015

C32 0.008 0.009 0.004 0.004 0.015 0.017 0.036 0.041 0.001 0.000 0.005

C34 0.010 0.006 0.005 0.003 0.021 0.013 0.050 0.030 -0.004 -0.002 -0.020

C35 0.017 0.032 0.008 0.016 0.035 0.064 0.082 0.152 0.015 0.007 0.070

C41 0.018 0.021 0.009 0.010 0.036 0.043 0.086 0.101 0.003 0.002 0.015

C43 0.008 0.009 0.004 0.004 0.015 0.017 0.036 0.041 0.001 0.000 0.005

C45 0.010 0.006 0.005 0.003 0.021 0.013 0.050 0.030 -0.004 -0.002 -0.020

C46 0.017 0.032 0.008 0.016 0.035 0.064 0.082 0.152 0.015 0.007 0.070

Table 4 . Reactivity descriptors of compound 2 computed using Mulliken population analysis (MPA)

Sites Local descriptors Dual descriptors

f- f+ σ- σ+ η- η+ ω- ω+ Δf Δσ Δω

C5 0.010 0.010 0.005 0.005 0.021 0.021 0.053 0.052 0.000 0.000 -0.001

C6 0.010 0.014 0.005 0.007 0.021 0.028 0.051 0.070 0.004 0.002 0.020

C7 0.020 0.024 0.010 0.012 0.041 0.049 0.102 0.120 0.004 0.002 0.018

C9 0.021 0.016 0.010 0.008 0.042 0.033 0.103 0.082 -0.004 -0.002 -0.021

C15 0.011 0.010 0.005 0.005 0.021 0.021 0.053 0.052 0.000 0.000 -0.001

C16 0.010 0.014 0.005 0.007 0.021 0.028 0.051 0.070 0.004 0.002 0.020

C17 0.020 0.024 0.010 0.012 0.041 0.049 0.102 0.120 0.004 0.002 0.018

C19 0.021 0.016 0.010 0.008 0.042 0.033 0.103 0.082 -0.004 -0.002 -0.021

C30 0.017 0.021 0.008 0.010 0.035 0.042 0.086 0.104 0.004 0.002 0.018

C31 0.016 0.024 0.008 0.012 0.033 0.049 0.081 0.122 0.008 0.004 0.041

C32 0.010 0.010 0.005 0.005 0.020 0.020 0.050 0.050 0.000 0.000 0.000

C34 0.009 0.008 0.004 0.004 0.018 0.016 0.045 0.040 -0.001 0.000 -0.005

C40 0.017 0.021 0.008 0.010 0.035 0.042 0.086 0.104 0.004 0.002 0.018

C41 0.016 0.024 0.008 0.012 0.033 0.049 0.081 0.122 0.008 0.004 0.041

C42 0.010 0.010 0.005 0.005 0.020 0.020 0.050 0.050 0.000 0.000 0.000

C44 0.009 0.008 0.004 0.004 0.018 0.016 0.045 0.040 -0.001 0.000 -0.005

The results of Table 4 predict that the C9 and C19 sites are the most favored sites face to electrophilic attacks. In the case of

Table 5 gathers the results of local index calculations and dual reactivity descriptors, using MPA population analysis at the computation level B3LYP/6 311G(d,p). It emerges that an electrophilic attack probably occurs on the C9 and C19 atoms, because the dual descriptors take negative values for these latter sites. However, C31 and C41 sites are more favorable to nucleophilic attacks.

As shown in the previous tables, the local indices as well as the dual descriptors derived from the MPA analysis predict a maximum value for the C9 and C19 atoms by promoting them for an

electrophilic attack. Moreover, based on the values of the various indices, we can conclude the nucleophilic attack occurs primarily on carbon C34 and C45.

At the end of our study, we can note that the local and dual reactivity descriptors computed using the B3LYP method with the 6-311G (d, p) base suggest that it is the C32 and C42 carbons that are the most favorable sites for electrophilic attacks. This results disagree with those previously obtained with compounds 1 to 4 for which, the C9 and C19 sites are the most privileged for the electrophilic attack.

Table 5. Reactivity descriptors of compound 3 computed using Mulliken population analysis (MPA)

Sites Local descriptors Dual Descriptors

f- f+ σ- σ+ η- η+ ω- ω+ Δf Δσ Δω

C5 0.011 0.012 0.005 0.006 0.022 0.024 0.051 0.055 0.001 0.000 0.004

C6 0.011 0.015 0.005 0.007 0.022 0.031 0.050 0.070 0.004 0.002 0.021

C7 0.021 0.024 0.010 0.012 0.044 0.050 0.099 0.114 0.003 0.002 0.016

C₉ 0.021 0.017 0.010 0.008 0.044 0.035 0.100 0.079 -0.005 -0.002 -0.021

C15 0.011 0.012 0.005 0.006 0.022 0.024 0.051 0.055 0.001 0.000 0.004

C16 0.011 0.015 0.005 0.007 0.022 0.031 0.050 0.070 0.004 0.002 0.021

C17 0.021 0.024 0.010 0.012 0.044 0.050 0.099 0.114 0.003 0.002 0.016

C19 0.021 0.017 0.010 0.008 0.044 0.035 0.100 0.079 -0.005 -0.002 -0.021

C30 0.018 0.022 0.009 0.011 0.038 0.046 0.086 0.103 0.004 0.002 0.017

C31 0.017 0.025 0.008 0.012 0.036 0.052 0.082 0.118 0.008 0.004 0.036

C32 0.011 0.007 0.005 0.004 0.023 0.015 0.052 0.035 -0.004 -0.002 -0.017

C34 0.010 0.006 0.005 0.003 0.020 0.012 0.045 0.028 -0.004 -0.002 -0.017

C40 0.018 0.022 0.009 0.011 0.038 0.046 0.086 0.103 0.004 0.002 0.017

C41 0.017 0.025 0.008 0.012 0.036 0.052 0.082 0.118 0.008 0.004 0.036

C42 0.011 0.007 0.005 0.004 0.023 0.015 0.052 0.035 -0.004 -0.002 -0.017

C44 0.010 0.006 0.005 0.003 0.020 0.012 0.045 0.028 -0.004 -0.002 -0.017

Table 6. Reactivity descriptors of compound 4 computed using Mulliken population analysis (MPA)

Sites Local descriptors Dual descriptors

f- f+ σ- σ+ η- η+ ω- ω+ Δf Δσ Δω

C5 0.007 0.006 0.004 0.003 0.015 0.011 0.042 0.031 -0.002 -0.001 -0.011

C6 0.011 0.008 0.006 0.004 0.022 0.016 0.064 0.045 -0.003 -0.002 -0.018

C7 0.021 0.019 0.011 0.010 0.040 0.038 0.117 0.110 -0.001 -0.001 -0.007

C9 0.041 0.018 0.021 0.009 0.081 0.035 0.236 0.103 -0.023 -0.012 -0.133

C15 0.007 0.006 0.004 0.003 0.014 0.011 0.042 0.031 -0.002 -0.001 -0.011

C16 0.011 0.008 0.006 0.004 0.022 0.016 0.064 0.045 -0.003 -0.002 -0.019

C17 0.021 0.019 0.011 0.010 0.040 0.038 0.117 0.110 -0.001 -0.001 -0.007

C19 0.042 0.018 0.021 0.009 0.081 0.035 0.236 0.103 -0.023 -0.012 -0.133

C30 0.014 0.012 0.007 0.006 0.028 0.023 0.080 0.066 -0.003 -0.001 -0.014

C32 0.009 0.018 0.005 0.009 0.018 0.035 0.052 0.101 0.009 0.004 0.049

C34 0.004 0.035 0.002 0.018 0.007 0.069 0.021 0.201 0.032 0.016 0.180

C35 0.015 0.025 0.008 0.013 0.030 0.049 0.086 0.142 0.010 0.005 0.056

C41 0.014 0.012 0.007 0.006 0.028 0.023 0.080 0.066 -0.003 -0.001 -0.014

C43 0.009 0.018 0.005 0.009 0.018 0.035 0.052 0.101 0.009 0.004 0.049

C45 0.004 0.035 0.002 0.018 0.007 0.069 0.021 0.201 0.032 0.016 0.180

Table 7. Reactivity descriptors of compound 5 computed using Mulliken population analysis (MPA)

Sites Local descriptors Dual descriptors

f- f+ σ- σ+ η- η+ ω- ω+ Δf Δσ Δω

C5 0.009 0.013 0.005 0.006 0.019 0.027 0.038 0.053 0.004 0.002 0.014

C6 0.006 0.015 0.003 0.007 0.013 0.030 0.025 0.059 0.008 0.004 0.034

C7 0.016 0.024 0.008 0.012 0.033 0.048 0.065 0.095 0.007 0.004 0.030

C9 0.018 0.015 0.009 0.008 0.036 0.031 0.071 0.062 -0.002 -0.001 -0.009

C15 0.009 0.013 0.005 0.006 0.019 0.027 0.038 0.053 0.004 0.002 0.015

C16 0.006 0.015 0.003 0.007 0.013 0.030 0.026 0.059 0.008 0.004 0.033

C17 0.016 0.024 0.008 0.012 0.033 0.048 0.065 0.095 0.007 0.004 0.030

C19 0.018 0.015 0.009 0.008 0.036 0.031 0.071 0.062 -0.002 -0.001 -0.009

C30 0.020 0.024 0.010 0.012 0.040 0.050 0.080 0.099 0.005 0.002 0.019

C31 0.017 0.020 0.008 0.010 0.035 0.040 0.070 0.079 0.002 0.001 0.009

C32 0.014 0.001 0.007 0.001 0.028 0.003 0.056 0.005 -0.012 -0.006 -0.050

C34 0.013 0.006 0.007 0.003 0.027 0.011 0.054 0.023 -0.008 -0.004 -0.031

C40 0.020 0.024 0.010 0.012 0.040 0.050 0.080 0.099 0.005 0.002 0.019

C41 0.017 0.020 0.008 0.010 0.035 0.040 0.070 0.079 0.002 0.001 0.009

C42 0.014 0.001 0.007 0.001 0.028 0.003 0.056 0.006 -0.012 -0.006 -0.050

C44 0.013 0.006 0.007 0.003 0.027 0.011 0.054 0.023 -0.008 -0.004 -0.031

Local indices of reactivity ( , and ) as well as the dual descriptors ( ∆ , ∆ and ∆ ), provide the highest value at the C6 and C16 sites. Thus the latter should be the most reactive sites with regard to a nucleophilic attack.

4. CONCLUSION

The maps of electrostatic potentials showed that areas of high electron densities are located around the heteroatoms. The environments of the carbon atoms are globally positive. The global and local indices and the dual reactivity descriptors were calculated. The analysis of the frontier molecular orbitals and the global reactivity indices showed that compound 4 is the most polarizable, has the highest chemical reactivity and the lowest kinetic stability among the studied molecules. In contrast, compound 5 is shown to be the least polarizable with the lowest chemical reactivity and high kinetic stability. Local descriptors obtained by the Mulliken population analysis method indicate that the C9 and C19 atoms for compounds 1 to 4 or C32 and C42 of compound 5 are the preferred sites of electrophilic attack. These interesting results can be used as a precursor for the synthesis of new Schiff bases derived from Dapsone.

COMPETING INTERESTS

Authors have declared that no competing interests exist.

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