Analysis of the structural, spectroscopic, and molecular electrostatic potential (MESP) of (amino)carbonothionyl (nitro)benzamide derivatives

Article abstract of DOI:10.1080/10426507.2021.1920589

This study examined the structural and spectroscopic properties of ten synthesized derivatives of carbonothionylbenzamide. These nitro group based molecules are five meta- (named M) and five para- (named P) compounds. These compounds showed no significant

Full text of DOI:10.1080/10426507.2021.1920589

Phosphorus, Sulfur, and Silicon and the Related Elements
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Analysis of the structural, spectroscopic, and
molecular electrostatic potential (MESP) of
(amino)carbonothionyl (nitro)benzamide
derivatives
Omotola M. Fayomi, Adebayo A. Adeniyi & R. Sha’Ato
To cite this article: Omotola M. Fayomi, Adebayo A. Adeniyi & R. Sha’Ato (2021): Analysis of the
structural, spectroscopic, and molecular electrostatic potential (MESP) of (amino)carbonothionyl
(nitro)benzamide derivatives, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2021.1920589
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2021.1920589
SHORT COMMUNICATION
Analysis of the structural, spectroscopic, and molecular electrostatic potential
(MESP) of (amino)carbonothionyl (nitro)benzamide derivatives
Omotola M. Fayomia , Adebayo A. Adeniyib,c , and R. Sha’Atoa
b
aDepartment of Chemistry, University of Agriculture Makurdi, Makurdi, Benue State, Nigeria; Department of Chemistry, Faculty of Natural
c
and Agricultural Sciences, University of the Free State, Bloemfontein, South Africa; Department of Industrial Chemistry, Faculty of Science,
Federal University Oye Ekiti, Nigeria
ABSTRACT
ARTICLE HISTORY
Received 5 November 2020
Accepted 19 April 2021
This study examined the structural and spectroscopic properties of ten synthesized derivatives of
carbonothionylbenzamide. These nitro group based molecules are five meta- (named M) and five
para- (named P) compounds. These compounds showed no significant difference in their IR spec-
tra from each other despite the positions of their nitro-substituent. The amino substituent has a
long-range effect on the atomic and bond properties associated with C ¼ O and C ¼ S of the car-
bonothionylamide moiety supported by the 13C NMR shielding, IR wavenumber, and bond
strength. The meta-molecules were more thermodynamically stable than the para-molecules,
though with lower band gap difference, they are of higher HOMO and LUMO energy levels. Total
stability energy of the fragment interaction from the meta- to para-molecule was relatively small.
The meta-derivatives have a more electron-rich center than the para-compounds with lower
molecular electrostatic potential values associated with Vmin, Vmax, and VS. Therefore, the order of
the electron-rich center, Vmin in the meta-molecules were: 2M > 5M > 4M > 1M > 3M and were
found close to the C ¼ O group of the carbonothionylamide unit of the fragment 2. The diethylni-
tro groups in molecules 3M or 3P have shown to be more susceptible at fragment 2 to nucleo-
philic attack to enhance their bidentate bonding behavior.
KEYWORDS
Spectroscopy; stability;
fragment interaction; NEDA
analysis; MESP
GRAPHICAL ABSTRACT
Introduction
as halogens causes a shift in the electron distribution of the
compounds, which have enhanced the activity of these com-
pounds.[4] Theoretical calculations of these compounds have
helped in an understanding of the structural–activity rela-
tionship to develop methods for better molecular design.
Carbonothionylbenzamide derivatives coordinate with metal
atoms to form stable metal complexes.[5–10] Most times, car-
bonothionylbenzamide derivatives chelate with the metal
Carbonothionylbenzamide derivatives have been much
researched due to their versatility in different fields such as
biology, medicine,[1] and agriculture.[2] These compounds,
through their donor atoms and the electron density, inhibit
microbial agents, regulate plant growth,[2] and cata-
lyze reactions.[3]
Compounds with additional substituents have been
reported with higher activity. The effect of substituents such atom as bidentate compounds via their donor sites.[11]
CONTACT Omotola M. Fayomi
Makurdi, Benue State, Nigeria; Adebayo A. Adeniyi
of the Free State, Bloemfontein, South Africa.
omotolafayomi@gmail.com, fayomi.omotola@uam.edu.ng
Department of Chemistry, University of Agriculture Makurdi,
ade4krist@gmail.com
Department of Chemistry, Faculty of Natural and Agricultural Sciences, University
Supplemental data for this article can be accessed online at https://doi.org/10.1080/10426507.2021.1920589.
ß 2021 Taylor & Francis Group, LLC

2
O. M. FAYOMI ET AL.
Figure 1. Synthesis of 1P.
Figure 2. Schematic representation of the synthesis of 3P.
These metal complexes are widely applied as antifungal,[12] obtained for 4P. The respective meta-structure were less
antibacterial,[13] and herbicidal[14] agents.
shielded as found for 3M [161.87 (C 5 O) and 178.60
(C 5 S)] and 4M [160.52 (C 5 O) and 181.46 (C 5 S)].[17]
A
Considering these activities, this work focuses on the syn-
thesis, characterization, and computational studies of five
meta (M)-nitro and five para (P)-nitro carbonothionylbenza-
mide molecules which will provide insight into their struc-
tures. The interest is to analyze the changes in the
spectroscopic, structural, molecular electrostatic potential
(MESP), and fragment interaction of the molecules as results
of the changes in the type of the substituents and the pos-
ition of the NO2 group (metal or para).
stronger long-range effect on the shielding tensor was
obtained by the nature of the substituents on the N(R1)R2
that defined the derivatives compared to the effect of the
para and meta position of the NO2 as molecule 3P and 3M
had lower shielding compared to 4P and 4M. Also, the sub-
stituent effects of the N(R1)R2 strongly affect the IR vibra-
tions position as the C ¼ O and C ¼ S vibrations of the 3P
[1686 (C ¼ O), 1347 (C ¼ S)] and 3M [1682 (C ¼ O), 1346
(C ¼ S)] was lower in wavenumber compared to that of 4P
[1721 (C ¼ O), 1348 (C ¼ S)] and 4M [1702 (C ¼ O),
1354 (C ¼ S)].[18]
Results and discussion
Synthesis and characterization of the compounds
The synthesis and characterization of 1P, 1M, 2M, and 2P
have been reported earlier by Fayomi.[15] The reaction which
involved condensation of the nitro-benzoylchloride followed
by the addition of an amine is described in Figure 1.
However, the synthesis of 3M–5M and 3P–5P had some
modifications as shown in Figure 2. Both 5P and 5M have
their synthetic and spectroscopic studies reported in previ-
ous work.[16]
The geometrical and spectroscopic properties of the
derivatives of carbonothionylbenzamide
To gain better insight into the spectroscopic and structural
properties of the ten derivatives of carbonothionylbenza-
mide, computational modeling was used and the structures
of the optimized geometries of the molecules are shown in
Figure 4.
The electronic effects of the different chemical units
around the carbonothionylamide unit are presented by frag-
mentation of each of the molecules into three different units
as indicated in Figure 3 and Supplemental Material Figure
S1. The chemistry of the carbonothionylamide unit (frag-
ment 2) is very significant in determining its stability and
coordination with metal atom when acting as a bidentate
ligand.[19] All the optimized geometries were characterized
with zero imaginary frequency indicating their local min-
It is imperative to note that these compounds were
included in this work to study some other properties using
computational methods.
The experimental results of the 13C NMR showed that
the para or meta position of the NO2 has a long-range
shielding effect of the carbon atoms of C ¼ O and C ¼ S on
fragment 2 of the molecules (Figure 3). The para position of
NO2 resulted in high shielding effect of the two C atoms,
shielding tensors of 162.66 (C 5 O) and 179.65 (C 5 S) were
obtained for 3P, and 165.78 (C 5 O) and 183.67 (C 5 S) imum. The molecule 5P had the lowest carbonothionyl

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
Figure 3. Schematic molecular structures of molecules 3P, 4P, 3M, and 4M. The plane represented by dotted lines divides each carbonothionylamide molecule into
fragments and allows interactions. The numbering is for the explanation of their C-NMR.
(C ¼ S) bond distance indicating a stronger bond strength double bonds. The two N ¼ O of the nitro group of frag-
because of the effect of the dipyridyl-amino group (fragment ment 3 had the lowest bond order among all the expected
1) while 3P and its meta derivative, 3M had the longest double bonds besides the imidazoyl N ¼ C bond as a pecu-
liar feature of the 2M and 2P. All the molecules were char-
acterized with some two-bond distance interactions and the
bond distance indicating a weaker strength (Figure 4) as the
effect of diethyl-amino group of its fragment 1.[20,21]
In all the molecules, the meta-substituted (M) as a result O … O interaction of the nitro group of fragment 3 observed
of the para position of the nitro group on the benzyl unit of to be the strongest. The sulfur atom of fragment 2 is also
found to have significant hydrogen bond interaction with
the nitrogen atom of fragment 1 (S … N). The strong reson-
ance effect at N-C bond linking fragment 1 to fragment 2
was observed as this bond order increased by 1.10 in all the
molecules to the stronger two bond distance electron cou-
pling of S … N interaction.
fragment 3 was found to be relatively more thermodynamic-
ally stable than their corresponding para-substituted (P) as
evidenced from the lower energy and Gibbs free energy
(Supplemental Material Table S1). However, the para deriva-
tives had lower HOMO and LUMO energy level with a lon-
ger bandgap compared to the meta-substituted.
The selected bond distances and the bond order of the
optimized geometries for those that involved the N, O, and
S atoms are listed in Supplemental Material Table S2. A
higher twist in the dihedral angle that defined the plane
O ¼ C … S ¼ O in fragment 2 over their linking nitrogen
atom in each molecule (as shown in Figure 2 for 1P) was
noticed in 3P, followed by 3M, while the smallest was found
in 5M then 5P. Generally, there was a relatively greater twist
of this angle in the meta-substituted (M) than in the para-
substituted (P) except for the 2P. The single bonds (-) have
bond orders that are relatively close to the expected value of
1.00 but the double bonds especially the conjugated ones are
significantly lower than the expected value of 2.00. The
The IR spectra of the derivatives of
carbonothionylbenzamide
The computed IR spectra showed a significant correlation
with the experimental IR (Figure 5 and Supplemental
Material Figure S5) as a further confirmation of the experi-
mental structure of the molecules. Both experimental and
theoretical IR clearly showed no significant difference
between the meta nitro (M) and para nitro (P) molecules
(Supplemental Material Figure S5). The details of the types
of all the prominent IR and RAMAN vibrations (ꢀ20.00)
are described in the supplementary Material Table S3. The
C ¼ O bond of fragment 2 had the highest bond order of assigned spectra with the negative percentage contribution
approximately 2.00, the highest among the groups with in Supplemental Material Table S3 were characterized with

4
O. M. FAYOMI ET AL.
Figure 4. The optimized geometries of the ten derivatives of carbonothionylbenzamide molecules and the selected bonds distances and dihedral angle (fragment
2) in the plane as indicated with arrow lines in molecule 1P.
opposite vibrations that reduced the observed frequencies except in both 2P and 2M with three N-H vibrations
obtained at the wavelength. The stretching vibration of because of the presence of imidazole group.[22] Unlike the
C ¼ S in fragment 2 in many of the molecules were not stretching vibration of N-H, the stretching vibration of
found to be prominent. The IR and RAMAN wavelengths C ¼ O appeared stronger in IR spectra than RAMAN and
(in cmꢁ1) for the C ¼ S bonds were observed for the mole- within the range 1837–1910 cmꢁ1 in the molecules.
cules 1M, 2M, 3M, 4M, 5M, 1P, 2P, 3P, 4P and 5P at
803.36, 1145.03, 878.24, 875.03, 804.30, 799.93(781.10),
The UV spectra of the derivatives of
872.98(429.35), 871.61, 879.83 and 805.64, respectively,
carbonothionylbenzamide
where the values in parentheses are the second wavelength
of C ¼ S vibration in the same molecule. The bending vibra-
The computed UV data agreed with the experimental UV
tional angle C-N-C in the fragment 2 appeared at the wave-
length (cmꢁ1) of 184.34(156.83), 173.52, 181.03, 177.76,
193.13, 158.96, 190.36, 173.11, 176.63, 158.96 in the mol-
ecule 1M, 2M, 3M, 4M, 5M, 1P, 2P, 3P, 4P, and 5P, respect-
ively. The frequency of C-N-C bending vibration appeared
at 0.20–5.10 in all the molecules. The stretching vibrations
of the N-H in the fragment 2 in all the molecules appeared
data. However, the computed absorption peaks appeared at
relatively lower wavelength (Figure 6 and Supplemental
Material Figure S6). A significant difference in the excitation
frequency and wavelength was observed between the meta
nitro (M) and para nitro (P) molecules in both the experi-
mental and computational methods.
The experimental absorbance depended mostly on the
at 3538 to 3640 cmꢁ1 having stronger RAMAN peak than IR concentration of the molecules, and can only be explained

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
5
Figure 5. The experimental and theoretical IR with the theoretical Raman spectra for molecules 1M, 1P, 2M, and 2P.
Figure 6. The experimental and theoretical UV spectra for molecules 1M, 1P, 2M, and 2P.
in terms of the theoretical absorbance values. The hyper- of the para molecules 1P, 2P, 4P, 5P, and 5P appeared at
chromic shift to higher molar absorptivity (higher absorb- 467; 420; 476; 433; 410 nm, respectively. Both experimental
ance) occurred in the meta molecules of 1M and 2M than and theoretical clearly showed that 3P or 3M had the lowest
corresponding para-isomers 1P and 2P, possibly because of values of kmax while 4P or 4M had the highest. The observed
the carbonyl group or mono substitution on the nitro. The experimental order of the kmax of P followed the same order
opposite was observed in the molecules with di-substituents as that of M (4M > 2M > 1M > 5M > 3M). This transition in
of the nitro as the molar absorptivity of the meta isomers most of the molecules was from fragment 2 to fragment 3
3M, 4M, and 5M reduced than the para-substituted 3P, 4P, but different in 4M, and its para 4P, from fragment 2 to
and 5P (Supplemental Material Figure S6). The experimental fragment 1 (Supplemental Material Table S4). It was also
kmax for the meta-molecules and para-molecules are not sig- different in 5M and its para 5P where it was from fragment
nificantly different and are found around 300, 430, 360, 350, 1 to fragment 3. The kmax is mostly characterized with the
and 350 nm for molecules 1–5, respectively. The calculated transition from a lower HOMO or HOMO – 1 which are
kmax significantly varied, the values for the 1M, 2M, 3M, predominantly around the S-atom p-bonds (as shown sup-
4M, and 5M were 441; 416; 452; 477; and 422 whereas that plementary Material Table S5) to either LUMO or LUMO þ

6
O. M. FAYOMI ET AL.
Table 1. The contribution of the electrostatic (ES), polarizability (POL), electrical (EL ¼ ES þ POL þ SE), and charge transfer (CT) to the total stability interaction
energy (Etotal) in kcal/mol.
Molecule
Total SCF energy
Energy change
Energy of deletion
ES
POL
EL
CT
ETotal
1M
1P
2M
2P
3M
3P
4M
4P
–1316.82
–1316.82
–1579.49
–1579.49
–1246.14
–1246.14
–1549.29
–1549.29
–1581.35
–1581.36
–1319.00
–1319.00
–1581.70
–1581.70
–1248.49
–1248.49
–1551.43
–1551.43
–1583.42
–1583.42
2.18
2.18
2.22
2.21
2.35
2.35
2.14
2.14
2.07
2.06
–945.37
–941.66
–952.53
–938.51
–955.66
–951.13
–871.03
–867.33
–856.09
–851.95
36.57
36.39
–1.31
–19.62
–44.01
–45.46
–50.97
–52.30
–52.16
–45.85
–891.83
–888.06
–913.32
–906.02
–924.41
–920.12
–851.27
–847.99
–840.71
–834.17
–1368.57
–1366.80
–1392.01
–1386.42
–1476.20
–1474.71
–1341.76
–1341.77
–1298.69
–1289.59
–758.91
–754.92
–774.00
–764.58
–788.99
–785.17
–721.06
–717.20
–702.35
–698.30
5M
5P
1 that are also predominantly p-bonds. Therefore, this kmax nature of the fragment. A higher dipole moment of a fragment
ꢂ
absorption transition can be defined as p ! p transition in will have higher polarizability that will allow significant pene-
the ligands.[23]
tration of the electron from donor or acceptor depending on
whether it is positively or negatively charged. The higher the
value of induced dipole moment of a fragment that is nega-
tively charged, the higher its level of is being available for to
make a nucleophilic attack. In all the molecules (both P and M
molecules), the fragment 2 became more available for nucleo-
philic attack than other fragments except in the para-molecule
of imidazoyl derivative (2P) where the induced dipole of the
fragment 1 significantly increased more than other fragments.
This provided further insight into the reason for exaltation fre-
The highest wavelength toward the visible region in each
of the ligands was characterized mostly with HOMO to
LUMO except in 2M (HOMO ! L þ 1), 5M (H –
1!LUMO) and 2P (H – 1!LUMO). The highest wave-
length absorption was the predominant transfer of an elec-
tron from fragment 2 to fragment 3 in all the M and P
molecules except for the 5M and para form, 5P that was
predominantly from fragment 1 to fragment 3. The HOMO
and H þ 1 were predominantly from fragment 2 except in
5M and 5P where the H þ 1 is fragment 1 while LUMO in
all the molecules was fragment 3 as shown in Supplemental
Material Table S6. The explanation agreed with the highest
wavelength transition in 5M and 5P because of their signifi-
ꢂ
quency of the p–p transition (to 257.45 nm) in 2P which sig-
nificantly got higher than the 2M and other molecules. The
availability of fragment 2 for a nucleophilic attack made it
important for metal coordination with the expected reaction
cant transition from fragments 1 through to 3, contrary to for these kinds of bidentate ligands. The values of the induced
other molecules of which their transition is from fragment 2 dipole for fragment 2 were relatively in a close range in all the
to 3. Details of each fragment contribution to the first six molecules but that of the molecule 3M and 3P have the highest
HOMO and LUMO energy levels are presented in tendency for the nucleophilic attack and the highest induced
Supplemental Material Table S6. The HOMO to LUMO energy besides the fragment of the para imidazoyl molecule 2P.
transition from the table had the smallest absorptivity and
No significant changes were observed in the induced dipole of
ꢂ
can therefore be assigned as the n!p electron transition. the fragments in each molecule from its meta- to para-substi-
This is presented from the features of the orbitals in the tuted compounds except only in 2P as previously explained.
Supplemental Material Table S5, where the HOMO predom- The predicted positive sign on fragment 2 showed that it acted
inantly is present around the S atom lone pair and the as the strong electrophilic center and well predisposed to
LUMO at the fragment 3 benzene p-bonds.
strong nucleophilic attack in all the ligands.
The total stability energy of intra-fragment interaction
and the contribution of the electrostatic (ES), polarizability
(POL), electrical, and charge transfer (CT) are shown in
Table 1. The level of contributions of different factors to the
stability of the intra-fragment interactions is in the order of
CT > ES > EL > POL. In all the molecules, there is a rela-
tively small decrease in the total stability energy of the frag-
ment interaction from the meta-substituted (M) to para-
substituted compounds (MOF) which furthers the insight
into the reason. Whereas, the M compounds appeared
thermodynamically more stable. Both the 3M and 3P, which
had the highest values of the induced dipole for fragment 2,
were relatively stable for inter-fragment interactions com-
pared to other molecules.
Fragment interactions
The natural energy decomposition analysis (NEDA) analysis
was used to compute the contribution of each of the frag-
ments to the stability of the molecules and natural bond order
(NBO)[24] method was used for the nature of the intramolecu-
lar charge transfer. The data generated for each of the frag-
ment energy and dipole in the absence of the other fragments
(def), in the presence of other fragments (cp), and the differ-
ence between the two states (ind) for each of the molecules
are shown in Supplemental Material Table S6. The contribu-
tion of the electrostatic (ES), polarizability (POL), electrical
(EL ¼ ES þ POL þ SE), and charge transfer (CT) to the total
stability energy (Etotal) of the intra-fragment interaction
within each of the molecules are shown in Table 1.
The MESP analysis
The induced dipole of each fragment in Supplemental
Material Table S7 shows the level of its predisposition to The only possible existence of Vmax is those associated with
nucleophilic attack or electrophilic attack depending on the the nuclei as it has been pointed out that Vmax does not

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
7
position Vmin was found closely positioned to the C ¼ O
group of the carbonothionylamide unit of the fragment 2 and
Vmax directly on top of the hydrogen atom of the N-H group
of the amide unit of fragment 2 as depicted for 1P in the
MESP surface plot (Figure 8).
Atomic electron susceptibility
The relative ability of each of the atoms in a molecule to act
as electrophilic (–ve), nucleophilic (þve), and radical attack
site can best be understood using Fukui indices. The expres-
sion for the Fukui indices usually is derived from the elec-
tronic density v(r) for the change in the number of the
electrons (N) under a constant external potential v(r):[33]
Figure 7. The change in the computed MESP values of DVmin, DVmax, and low-
est value of the DVatom of the molecules from that of the 1M (all in kcal/mol).
ꢀ
ꢁ
dq
FðrÞ
¼
dN
v
Table 2. The computed MESP values of Vmin, Vmax and that of the sulfur
atom, VS of the molecules.
The highly nucleophilic or electrophilic or radical sites
are expected to have a higher value of Fukui function (fj).[34]
The condensed expression of the atomic Fukui functions for
jth atom site can be calculated from the atomic charges q(N)
for the electrophilic (fj–) or nucleophilic (fjþ) or radical (fj0]
as follows:
Molecules
Vmin
Vmax
VS
1M
1P
2M
2P
3M
3P
4M
4P
5M
5P
–42.04
–41.00
–49.44
–47.47
–28.67
–28.88
–43.92
–42.65
–46.78
–43.59
58.50
60.99
58.29
59.62
39.94
42.50
43.32
46.44
42.60
46.50
–37202.05
–37200.34
–37212.71
–37209.24
–37209.64
–37208.25
–37206.68
–37204.84
–37204.10
–37199.03
fjꢁ
¼
¼
qjðNÞ ꢁ qj N ꢁ 1
ð
Þ
fjþ
qj N þ 1 ꢁ qjðNÞ
ð
Þ
ꢂ
ꢃ
1
All the values in kcal/mol.
fj0
¼
ð Þ
ð Þ
qj N þ 1 ꢁ qj N ꢁ 1 %
2
exist in the three dimensions of the MESP surface.[25–28]
The values of the electrophilic (fj–), nucleophilic (fjþ),
Therefore, the Vmax reported in this work represent only the and radical (fj0] Fukui indices for the sulfur, oxygen, nitro-
most positive or highest values of the MESP surface.[29–31] gen, and carbon atoms in each of the molecules are pre-
The importance of application of MESP for the analysis of sented in the supplementary Material Table S8 while their
the effect of para-substitution on benzene has been reported MESP surfaces (MEPS) mapping showing the atomic sites
for electrophilic, nucleophilic, and radical reactions are
The significance of the Vmin and Vmax was that a more shown in Figure 9 and Supplemental Material Figure S7.
negative value of Vmin indicated a higher electron density The atomic charges from the natural population analysis
in the literature.[32]
whereas more positive values of Vmax implied a more elec- (NPA) were used to compute all the Fukui indices because of
tron-deficient positions in the molecule. The change in the the ability to differentiate the reactive site[35] and its insensitive
computed MESP analysis: DVmin, DVmax, and lowest value of to basis set because of the use of the occupancy-weighted sym-
the DVatom, were obtained by subtracting the values obtained metric orthogonalization procedure to transform the non-
for 1M from each of the other molecules as shown in Figure 7. orthogonal atomic orbitals into an orthonormal set.[36]
The respective values of Vmin, Vmax, and Vatom for each of the Therefore, the orbitals of highest occupancy were strongly pre-
molecules are itemized in Table 2. The values of the reported served while those of negligible occupancy can be distorted
V
atom are the highest magnitude obtained among all the atoms freely to achieve orthogonality.[35] However, NPA tends to
which were found to correspond to that of the sulfur atom.
overestimating the ionicity.[37] All the negative values of Fukui
All the meta derivatives had more electron-rich centers indices are usually disregarded and the site with the highest
compared to their para molecules as evident from the lower value of Fukui indices indicates a high reactivity but in some
energy values of Vmin, Vmax, and VS (Figure 7, Table 2). The cases does not necessarily be the most reactive site.[35,38,39]
molecules with di-substituent on the nitro unit (3P–5P or
As clearly shown in both Figure 9 and Supplemental
3M–5M derivative) had less electron-deficient center than the Material Figure S7, the strongest mapped area as the electro-
mono-substituted or carboxylic containing nitro unit (1P–2P philic site is fragment 1 while fragments 2 and 3 act as the
or 1M–2M derivatives) as evident from their Vmax values. The strong nucleophilic sites. A closer look at the atomic contri-
order of the electron-rich center Vmin in the molecules using butions according to their Fukui indices (Supplemental
the meta-substituted derivatives was 2M > 5M > 4M > Material Table S8) shows that the main electrophilic center
1M > 3M. Though 3M or 3P were found to have less electron- happened to be the nitro group (NO2) while the S atom, the
rich center Vmin, yet had a very significant atomic potential of most significant nucleophilic center. An agreement with the
the sulfur atom VS in comparison to 4M, 5M, and 1M. The predominance of the HOMO in the S atom of fragment 2,

8
O. M. FAYOMI ET AL.
Figure 8. The MESP surface, showing the position of the potential of the sulfur atom (Vs), minimum (Vmin), maximum (Vmax) potential of molecule 1M and 1P. The
values are in kcal/mol.
Figure 9. The MESP surfaces (MEPS) of the molecules in their neutral, electrophilic (–) and nucleophilic (þ) states for molecules 1M, 2P, 2M, and 2P.
and the LUMO predominantly in the nitro group of frag- histidine were purchased from Sigma-Aldrich. Diethylamine,
ment 3. The S atom in all the molecules also had a high ten- diphenylamine, 2,2-dipyridylamine, and ammonium thio-
dency of acting as a point for a radical attack in addition to cyanate were obtained and used as supplied.
Ethanol was distilled with Mg ribbon/iodine (which
remove the impurities), and stored with molecular sieve 3 Å.
Other solvents, such as methanol, ethyl acetate, n-hexane,
acetone, diethyl ether, and dichloromethane, were stored
undistilled with molecular sieve 3 Å. Chloroform, and dis-
tilled water were used without further purification. Besides,
its properties as the nucleophilic center.
Synthetic and computational methods
Experimental materials
Analytical grade reagents were used for synthesis. 3-Nitro
benzoyl chloride, 4-nitro benzoyl chloride glycine, and dimethyl sulfoxide and deuterated chloroform (CDCl3) were

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
9
purchased from Sigma-Aldrich and deuterated dimethyl sulf- 1.26 (s, 3H, J ¼ 10.2 Hz, H-10), 1.26 (s, 3H, J ¼ 7.0 Hz, H-
12). 13C NMR (DMSO-d6), ppm: d 122.96 (C-1), 178.60 (C-
oxide
(DMSO-d6)
was
purchased
from
Merck
8), 161.87 (C-7), 148.36 (C-2), 137.37 (C-6), 133.61 (C-5),
130.17 (C-4), 127.23 (C-3), 47.92 (C-9), 47.92 (C-11), 13.43
(C-10), 13.43 (C-12). IR, ꢀ (cmꢁ1): 3275 (N-H), 1682
(C ¼ O), 1346 (C ¼ S), 1659 (C ¼ C). (TOF-ESI MS) m/z
(%): Calculated 280.0834. Found [M-H]– 280.0846 (100).
Chemical Limited.
Experimental equipment and methods
StuartTM Scientific apparatus SMP 3 was used without cor-
rection to determine the melting point of the compounds.
Waters Micromass LCT Premier MS instrument equipped
with an electrospray ionization (ESI) source and a time-of-
flight (TOF) mass analyzer was for mass of the molecular
ions and fragments. The infrared spectroscopy was measured
by ATR Perkin Elmer Spectrum 100 spectrometer. Likewise,
both 1H and 13C NMR were recorded on BRUKER
400 MHz spectrometer (AVANCEIII 400) in DMSO-d6 and
CDCl3 with TMS as an internal standard. NMR data were
expressed in ppm. The UV/visible spectra were taken on a
Shimadzu NIS-3600 containing quartz cuvettes having a
path length of 1 cm in the range 200–400 nm for UV and
400–900 nm for the visible region.
4P: N,N-(diphenyl-2-thiocarbamoyl)-4-(4-nitro phenyl
carboxamide)
Appearance: Yellow solid. Yield: 5.97 g (79%); Melting point
1
(144–146 ꢃC). H NMR, 400 MHz (DMSO-d6), ppm: d 10.15
(d, 1H, 2-NHCO), 8.25 (d, 1H, J ¼ 8.8 Hz, H-5), 8.25 (d, 1H,
J ¼ 8.8 Hz, H-7), 8.15 (d, 1H, J ¼ 5.0 Hz, H-4), 8.15 (d, 1H,
J ¼ 5.0 Hz, H-8), 7.73 (m, 1H, J ¼ 8.5 Hz, H-11), 7.73 (m,
1H, J ¼ 8.5 Hz, H-13), 7.73 (m, 1H, J ¼ 7.8 Hz, H-17), 7.73
(m, 1H, J ¼ 7.8 Hz, H-19), 7.60 (m, 1H, J ¼ 8.5 Hz, H-12),
7.60 (m, 1H, J ¼ 8.5 Hz, H-18), 6.95 (d, 1H, H-10), 6.95 (d,
1H, H-14), 6.95 (d, 1H, H-16), 6.95 (d, 1H, H-20),. 13C
NMR (DMSO-d6), ppm: d 183.67 (C-1), 165.78 (C-2),
149.48 (C-6), 143.36 (C-9), 143.36 (C-15), 139.20 (C-3),
130.02 (C-11), 130.02 (C-19), 130.02 (C-13), 130.02 (C-17),
128.87 (C-4), 128.87 (C-8),123.24 (C-5), 123.24 (C-7), 119.60
(C-10), 119.60 (C-14), 119.60 (C-16), 119.60 (C-20), 116.67
(C-12), 116.67 (C-18). IR, ꢀ (cmꢁ1): 3382 (N-H), 1721
(C ¼ O), 1348 (C ¼ S), 1697 (C ¼ C). (TOF-ESI MS) m/z
(%): Calculated 376.0834. Found [M-H]– 376.1066 (6).
Experimental structural elucidation
We analyzed five meta nitro (M) and five para nitro (P)
benzamide carbonothionyl derivatives (see Supplementary
Material Figure S1). All the ten ligands tagged 1P, 1M, 2P,
2M, 3P, 3M, 4P, 4M, 5P, and 5M were synthesized and
characterized experimentally. Only the experimental charac-
terization of 3P, 3M, 4P, and 4M were reported in this work
while the rest were already reported by some of the authors
in the literature.[15,16] The 1H NMR, 13C NMR, and the
mass spectra for the molecule 3P, 3M, 4P, and 4M were part
of the supplementary (Supplemental Material Figures S2–S4)
and the characterization data are presented in the follow-
ing sections.
4M: N,N-(diphenyl-2-thiocarbamoyl)-4-(3-nitro phenyl
carboxamide)
Appearance: Yellow solid. Yield: 2.25 g (29.70%); Melting
1
point (110–112 ꢃC). H NMR, 400 MHz (DMSO-d6), ppm: d
8.67 (d, 1H, J ¼ 2.0 Hz, H-4), 8.32 (d, 1H, J ¼ 2.0 Hz, H-6),
7.91 (d, 1H, J ¼ 2.0 Hz, H-8), 7.54 (d, 1H, J ¼ 2.0 Hz, H-7),
7.31 (m, 1H, J ¼ 7.7 Hz, H-13), 7.32 (m, 1H, J ¼ 1.3 Hz, H-
11), 7.29 (m, 1H, J ¼ 7.7 Hz, H-17), 7.28 (m, 1H, J ¼ 1.3 Hz,
H-19), 7.23 (d, 1H, J ¼ 7.8 Hz, H-10), 7.21 (d, 1H, H-14),
7.19 (d, 1H, J ¼ 1.4 Hz, H-16), 7.17 (d, 1H, J ¼ 8.0 Hz, H-
20), 7.01 (m, 1H, J ¼ 7.3 Hz, H-18), 6.98 (m, 1H, J ¼ 1.1 Hz,
H-12). 13C NMR (DMSO-d6), ppm: d 181.46 (C-1), 160.52
(C-2), 148.22 (C-5), 143.13 (C-9), 143.13 (C-15), 134.44 (C-
3), 133.57 (C-8), 130.12 (C-17), 130.28 (C-7), 130.12 (C-11),
130.12 (C-13), 130.12 (C-19), 128.02 (C-6), 122.47 (C-4),
120.99 (C-10), 120.99 (C-14), 120.99 (C-16), 120.99 (C-20),
117.81 (C-12), 117.81 (C-18). IR, ꢀ (cmꢁ1): 3152 (N-H),
1702 (C ¼ O), 1354 (C ¼ S), 1591 (C ¼ C). (TOF-ESI MS)
3P: N,N-(diethyl-2-thiocarbamoyl)-4-(4-nitro phenyl
carboxamide)
Appearance: Yellow solid. Yield: 2.22 g (39.50%); Melting
1
point (147–149 ꢃC). H NMR, 400 MHz (DMSO-d6), ppm: d
10.95 (s, 1H, 7-NHCO), 8.32 (d, 1H, H-2), 8.32 (d, 1H, H-
4), 8.12 (d, 1H, H-1), 8.12 (d, 1H, H-5), 3.57 (m, 2H, H-11),
3.57 (m, 2H, H-9), 1.21 (s, 3H, H-10), 1.21 (s, 3H, H-12).
13C NMR (DMSO-d6), ppm: d 179.65 (C-8), 162.66 (C-7),
149.47 (C-3), 136.64 (C-6), 129.50 (C-1), 129.50 (C-5),
129.41 (C-4), 123.41 (C-2), 47.22 (C-9), 47.22 (C-11), 13.30
(C-10), 13.30 (C-12). IR, ꢀ (cmꢁ1): 3279 (N-H), 1686
(C ¼ O), 1347 (C ¼ S), 1645 (C ¼ C). (TOF-ESI MS) m/z
(%): Calcld 280.0834. Found [M-H]– 280.0965 (100).
m/z
(%):
Calculated
376.0834.
Found
[M-H]–
376.0934 (100).
Computational methods
3M: N,N-(diethyl-2-thiocarbamoyl)-4-(3-nitro phenyl
carboxamide)
The optimization of the molecules was carried out using the
hybrid DFT functional M062X that is known to be good for
thermodynamic and kinetic calculations[40] and basis set 6-
311G(d,p) in the Gaussian 09 (G09) package.[41] The associ-
Appearance: Brown solid. Yield: 1.00 g (58%); Melting point
1
(110–112 ꢃC). H NMR, 400 MHz (DMSO-d6), ppm: d 8.61
(d, 1H, J ¼ 8.2 Hz, H-1), 8.37 (d, 1H, J ¼ 7.4 Hz, H-3), 8.13
(d, 1H, J ¼ 1.8 Hz, H-5), 7.63 (d, 1H, J ¼ 8.0 Hz, H-4), 3.96 ated properties with the natural bond orbital (NBO) ana-
(m, 2H, J ¼ 7.6 Hz, H-9), 3.96 (m, 2H, J ¼ 7.6 Hz, H-11), lysis[42] and natural energy decomposition analysis

10
O. M. FAYOMI ET AL.
(NEDA)[43] were obtained using NBO 6.0G program[44] as was found close to the C ¼ O group of the carbonothionyla-
implemented in the FIREFLY 8.1.G[45] which is partially
mide unit of the fragment 2.
based on the GAMESS (US)[46] source code. The IR and
The presence of carboxylic or the mono-substitution of
RAMAN spectra assignments were carried out by the poten-
tial energy distribution (PED) analysis as implemented in
VEDA package.[47]
The MESP was computed from a standard equation at a
point r as:
the nitro group in the meta-substituted molecule 1M and
2M resulted in a hyperchromic shift to higher UV molar
absorptivity compared to their para-substituted molecule in
contrast to the di-substituted nitro compounds as the molar
absorptivity of the meta-substituted ꢁ 3M, 4M, and 5M is
lower than the para-substituted 3P, 4P, and 5P.
The longest wavelength toward the visible region in each
of the ligands was characterized mostly with HOMO
to LUMO.
N
0
3
0
X
ð Þ
ZA
q r d r
jr ꢁ r0j
V r ¼
ð Þ
ꢁ
jr ꢁ RAj
A
where ZA, RA, q(r0), and N represent the charge of nucleus
A, its position, electron density, and the total number of
nuclei, respectively. The critical points (CP) corresponding
The presence of the diethylnitro group in molecule 3M
or 3P resulted in a more susceptible fragment 2 to nucleo-
to (3, þ3) and by (3, ꢁ3) represent the MESP minima philic attack which enhanced their bidentate properties as
(Vmin) and MESP maxima (Vmax) on the MESP topology
analysis while the saddle points are represented with (3, þ1)
and (3, ꢁ1).[48]
ligand and also resulted in better fragment inter-
action energy.
The results of the Fukui indices show that the main elec-
trophilic center in the molecules was located on the nitro
group (NO2) while the S atom was the most significant
nucleophilic center. This justified for the S atom predomin-
antly to be HOMO and the LUMO was predominantly the
nitro group.
The molecular rendering was achieved using programs:
Chimera,[49] MarvinSketch,[50] Gnuplot,[51] and VMD.[52]
Conclusion
The experimental synthesis and computational study of five
meta nitro and five para nitro with carbonothionylbenza-
mide unit were carried out. Each of the ten molecules was
fragmented into three to gain better insight into the elec-
tronic communication, nucleophilicity, and stability. The
chemistry of the carbonothionylamide unit (fragment 2)
became very significant as it can determine its stability and
coordination with metal when acting as a bidentate ligand.
No significant difference was observed between the IR
spectra of meta-nitro (M) and para nitro (P) substituted
molecules according to the result obtained from both experi-
mental and theoretical methods.
Among all the atoms in the molecules, the sulfur atom
had the lowest atomic potential energy (Vatom) and more
pronounced
in
molecules
2M
and
3M
than
other compounds.
Acknowledgment
Authors thank CHPC for the simulation facilities.
Ethical statement/conflict
This study does not require any ethical clearance and also there is no
conflict of interest.
The type of the substituent on the amino group of frag-
ment 1 have a long-range effect on the 13C NMR shielding
and IR wavenumber as it resulted in higher shielding tensor
of the carbon atoms in C ¼ O and C ¼ S and also higher
wavenumber for the vibration C ¼ O and C ¼ S in molecule
Funding
The authors acknowledge the University of KwaZulu Natal Durban,
4P or 4M because of the presence of dibenzylamino group University of the Free State, and the NRF in South Africa for finan-
cial support.
compared to that of 3P or 3M that have the lowest because
of the presence of diethylamino group.
The presence of dipyridylamino group in 5P and 5M
resulted in stronger carbonothionyl (C ¼ S) bond while
ORCID
diethylamino group led to weaker bond as found in 3P
Omotola M. Fayomi
Adebayo A. Adeniyi
http://orcid.org/0000-0001-7971-605X
http://orcid.org/0000-0003-2421-1382
and 3M.
The meta position of the nitro unit (M) resulted in more
thermodynamically stable structures but has higher
a
HOMO and LUMO energy levels with lower band-gap com-
pared to the para (P) compounds. There was a little relative
reduction in the total stability energy of the fragment inter-
action from the meta- to para-substituted compounds.
All the meta derivatives had more electron-rich center
than the para-substituted compounds as evident from the
lower energy values of Vmin, Vmax, and VS. The order of the
electron-rich center Vmin in the molecules for the meta-sub-
stituted compounds was 2M > 5M > 4M > 1M > 3M, which
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