Theoretical and experimental NMR data of 3,5-dinitro-2-(2-phenylhydrazinyl) pyridine and of its 4- and 6-methyl derivatives

Article abstract of DOI:10.1016/j.molstruc.2013.03.052

3,5-Dinitro-2-(2-phenylhydrazinyl)pyridine and its methyl derivatives: 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 6-methyl-3,5-dinitro-2- (2-phenylhydrazinyl)pyridine were synthesized and characterized by ¹H NMR and ¹³C NMR. Calculations were also performed where the above molecules were optimized using the methods of density functional theory (DFT) with 6-31G(d,p) and 6-311G(d,p) basis sets. For all molecules studied, the lowest energy was obtained using the 6-311G(d,p) basis set. The GIAO/DFT (Gauge Invariant Atomic Orbitals/Density Functional Theory) calculations on the 6-311G and 6-311++G and 6-311G^* basis sets were carried out to determine proton and carbon chemical shifts and to find they were close to the experimental values. It has been also found that intramolecular hydrogen bonding exists between hydrogen atom (in 2-NH group) and oxygen atom (pyridine-3-NO₂). Moreover, resonances between pyridine ring and electron withdrawing 3-nitro group as well between that ring and the lone electron pair of NH group favor a co-planarity of the structure; this means a chelate ring created by above-mentioned intramolecular hydrogen bond is almost co-planar with pyridine ring.

Full text of DOI:10.1016/j.molstruc.2013.03.052

Journal of Molecular Structure 1043 (2013) 15–27
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Theoretical and experimental NMR data of 3,5-dinitro-2-(2-phenylhydrazinyl)
pyridine and of its 4- and 6-methyl derivatives
⇑
M. Wandas , Z. Talik
Department of Bioorganic Chemistry, Institute of Chemistry and Food Technology, University of Economics, 53-345 Wrocław, Poland
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
The NMR spectra of 3,5-dinitro-2-(2-phenylhydrazinyl)-pyridine and its methyl derivatives are discussed.
GIAO/DFT procedure is used for calculation of shielding constants.
Correlations between calculated and experimental chemical shifts are demonstrated.
Molecular structures of above pyridine compounds are determined.
a r t i c l e i n f o
a b s t r a c t
Article history:
3,5-Dinitro-2-(2-phenylhydrazinyl)pyridine and its methyl derivatives: 4-methyl-3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine were synthesized and
characterized by 1H NMR and 13C NMR. Calculations were also performed where the above molecules
were optimized using the methods of density functional theory (DFT) with 6-31G(d,p) and 6-311G(d,p)
basis sets. For all molecules studied, the lowest energy was obtained using the 6-311G(d,p) basis set.
The GIAO/DFT (Gauge Invariant Atomic Orbitals/Density Functional Theory) calculations on the 6-311G
and 6-311++G and 6-311Gꢁꢁ basis sets were carried out to determine proton and carbon chemical shifts
and to find they were close to the experimental values.
Received 15 February 2013
Received in revised form 24 March 2013
Accepted 25 March 2013
Available online 6 April 2013
Keywords:
1H and 13C NMR spectra
GIAO
It has been also found that intramolecular hydrogen bonding exists between hydrogen atom (in 2-NH
group) and oxygen atom (pyridine-3-NO2). Moreover, resonances between pyridine ring and electron
withdrawing 3-nitro group as well between that ring and the lone electron pair of NH group favor a
co-planarity of the structure; this means a chelate ring created by above-mentioned intramolecular
hydrogen bond is almost co-planar with pyridine ring.
3,5-Dinitro-2-(2-phenylhydrazinyl)pyridine
derivatives
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
ciency virus (HIV) as well as of hepatitis B virus (HBV), could be
used as therapeutic or preventive agents for hepatitis B and ac-
Pyridine compounds and their derivatives such as N-oxides are
a compound class of great scientific and practical importance. A
vast number of those compounds are used in pharmaceutical re-
search and industry but practical uses in the production of dye-
stuffs, antioxidants or copolymers are also known [1]. Biological
activities of heterocyclic compounds including nitro pyridines,
such as antibacterial or antifungal potency, have been the subject
of many studies [2]. In recent years, ruthenium complexes of o-tol-
ylazopyridine and 4-methyl-2-phenylazopyridine have been syn-
thesized and investigated due to their potential anticancer
activity [3–7]. An invention was reported [8], related to special
3-nitropyridine derivatives and their salts which, due to their
inhibitory activity against the proliferation of human immunodefi-
quired immune deficiency syndrome (AIDS).
Nitration of pyridine as electrophilic aromatic substitution pro-
ceeds with a great difficulty and only low yields of nitro pyridines
can be obtained by this way. However, novel methods developed
by Bakke [9] (using N2O5 dissolved in liquid SO2) and Katritzky
et al. [10] (with nitric acid in trifluoroacetic anhydride) made pos-
sible to generate the desired products with reasonable or even high
yields.
Hydrazinopyridines and their derivatives constitute a subclass
of pyridine compounds which may be interesting from scientific
point of view and, again, may be useful as pharmaceutical interme-
diates. Syntheses of ortho-vanillin-2-hydrazinopyridine (a com-
pound created by condensation of 2-hydroxy-3-methoxy-
benzaldehyde i.e. ortho-vanillin with 2-hydrazinopyridine) and of
organotin(IV) complexes of that compound as a ligand have been
carried out by Sam et al. [11]; those products showed moderate
⇑
Corresponding author. Tel.: +48 71 3680303; fax: +48 71 3680292.
E-mail address: maria.wandas@ue.wroc.pl (M. Wandas).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.03.052

16
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
or high activity against such types of bacteria as Bacillus cereus,
Staphylococcus aureus, Escherichia coli and Enterobacter aerogenes.
Pyridines with NHAX substituents in the two-position of the
ring may show tautomerism, i.e. they can exist in both amino
and imino forms [12]. While for NH2 and NH-alkyl groups the ami-
no form is predominant, the importance of imino form increases
considerably for electron-withdrawing X groups, especially such
as NO2 or CN. In the paper cited, the tautomerism and rotamerism
of 2-(2-phenylhydrazinyl)pyridine has been confirmed using NMR
technique.
(D) Synthesis of 3,5-dinitro-2-(2-phenylhydrazinyl)-pyridine (or
4 or 6-methyl derivatives) from 2-fluoro-3,5-dinitropyridine
(or 4 or 6-methyl derivatives).
Syntheses were carried out using 2-aminopyridine or its 4 or 6-
methyl derivatives (Fluka, purum, >99%) as initial compounds. The
product yields, referred to the substrate used in each step and to
the reaction stoichiometry, were as follows (for 2-aminopyridine,
2-amino-4-methylpyridine and 2-amino-6-methylpyridine as pri-
mary compounds, respectively):
In modern investigations of pyridine compounds, GIAO DFT
computational methods in the GAUSSIAN package are widely used
for theoretical calculations of molecules properties to confirm their
experimental NMR data [13–31].
Step (A) 48.3%, 42.1% and 56.1%.
Step (B) 63.0%, 60.1% and 74.1%.
Step (C) 44.3%, 44.3% and 41.1%.
Step (D) 72.1%, 45.3% and 42.6%.
Synthesis and molecular structure investigations of pyridine
compounds were being undertaken by the authors for many years
[32]. In most recent study [33], the molecular structure and 1H and
13C NMR spectra of the 4,40(or 6,60)-dimethyl-3,30-dinitro-2,
20-azo- and hydrazo-pyridine in the solid state and solution have
The last step (D) i.e. syntheses of 3,5-dinitro-2-(2-phenylhydr-
azinyl)pyridine, 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyri-
dine and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
has been carried out as condensations of 2-fluoro-3,5-dinitropyri-
dine or its 4-methyl or 6-methyl derivatives with phenylhydrazine.
0.01 mol of 2-fluoro-3,5-dinitropyridine or its methyl derivative
was dissolved in 10 ml of methanol; to this solution 0.02 mol of
phenylhydrazine (Sigma–Aldrich, purum, >95%) was added. The
reaction mixture was heated for 2 min at 60 °C and then allowed
to stand at room temperature for 24 h. Then, the solvent was dis-
tilled off under reduced pressure and the residue was extracted
with hot chloroform. The chloroform extract was evaporated to ob-
tain a dry residue which, subsequently, was treated with a small
amount of pharmaceutical petrol to remove traces of phenylhydr-
azine. The insoluble reaction product was filtered off, dried and
recrystallized.
been discussed. The present paper shows the results of 1H/13
C
NMR investigations and theoretical studies on the structure of
3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and of its methyl
derivatives.
2. Experimental
2.1. Synthesis
Compounds studied in this work i.e. 3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine and its methyl derivatives were synthesized
by the authors by methods published previously by Talik and Talik
[34,35]. The syntheses included several consecutive steps as pre-
sented in Scheme 1 for the first compound:
The elemental analyses and melting points were:
– For 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (recrystallized
from ethanol): C: 48.40 (calc. 48.00) H: 3.18 (calc. 3.30) N:
25.20 (calc. 25.45) 155 °C.
– For 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (recrys-
tallized from methanol): C: 50.30 (calc. 49.82) H: 3.80 (calc.
3.83) N: 24.48 (calc. 24.21) 131 °C.
– For 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (recrys-
tallized from methanol and acetonitrile): C: 50.20 (calc. 49.82)
H: 3.83 (calc. 3.83) N: 24.21 (calc. 24.21) 164 °C.
(A) Synthesis of 3 or 5-nitro-2-aminopyridine (or 4 or 6-methyl
derivatives) from 2-amino pyridine (or its 4 or 6-methyl
derivatives).
(B) Synthesis of 3,5-dinitro-2-aminopyridine (or 4 or 6-methyl
derivatives) from 5-nitro 2-aminopyridine (or 4 or 6-methyl
derivatives).
(C) Synthesis of 2-fluoro-3,5-dinitropyridine (or 4 or 6-methyl
derivatives) from 3,5-dinitro-2-aminopyridine (or
6-methyl derivatives).
4 or
Scheme 1. Scheme of synthesis of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and atom numbering of the final structure.

M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
17
Fig. 1. (a) 3D-image of the structure of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine with the dipole moment vector marked. (b) 3D-image of the structure of 4-methyl-3,5-
dinitro-2-(2-phenylhydrazinyl)pyridine with the dipole moment vector marked. (c) 3D-image of the structure of 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine with
the dipole moment vector marked.

18
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
Table 1
Table 1b
NAHꢃ ꢃ ꢃO geometries and NPA charges in atoms calculated using DFT (6,311Gꢁꢁ
)
Total Energies (TE) and Z-Point Vibration Energies (ZPVE) calculated using DFT (6-
31G(d,p)a and 6-311G(d,p)) methods for 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
(1), 4-methyl-3,5-dinitro -2-(2-phenylhydrazinyl)-pyridine (2) and 6-methyl-3,5-
dinitro -2-(2-phenylhydrazinyl)pyridine (3).
methods and experimental 1H NMR data of 3,5-dinitro-2-(2-phenylhydrazinyl)pyr-
idine (1), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (2) and 6-methyl-3,5-
dinitro-2-(2-phenylhydrazinyl)pyridine (3).
(1)
2.6343
1.01331
1.90738
126.05039
ꢂ7.35528
4.96078
ꢂ0.36978
(2)
(3)
2.63925
1.01424
1.90482
126.68957
ꢂ7.20329
4.76901
ꢂ0.37376
TE (kcal/mol)
ZPVE (kcal/mol)
Frequency calculations
R
Nꢃ ꢃ ꢃO/Å
RNAH/Å
Oꢃ ꢃ ꢃH/Å
2.62243
1.01064
1.90902
1
2
3
141.101a
140.431
159.616a
158.911
130.9170a
130.21191
148.51326a
147.76537
0 Imaginary
Frequencies
R
0 Imaginary
Frequencies
<NAHꢃ ꢃ ꢃO/°
124.96606
ꢂ16.82901
ꢂ25.14051
ꢂ0.390370
<CCNH/°
159.411a
158.626
147.76537a
147.37167
0 Imaginary
Frequencies
<CNOꢃ ꢃ ꢃH/°
N(2)AN(1)
ꢂ0.42668
0.43314
0.39409
ꢂ0.43413
ꢂ0.36440
10.00
ꢂ0.43222
0.42852
0.38728
ꢂ0.42591
ꢂ0.35898
8.19
ꢂ0.42816
0.43167
0.38988
ꢂ0.43570
ꢂ0.36599
9.90
N(2)AN(1)
HN(2)AN(1)H
HN(2)AN(1)H
ONOꢃ ꢃ ꢃHN(2)
The Gauge Invariant Atomic Orbitals (GIAOs) method is one of
the most common approaches for calculating isotropic nuclear
magnetic shielding tensors [13–31,37–43]. For the same basis set
size, GIAO method is often more accurate than those using other
approaches. The calculations reported were performed in chloro-
ONOꢃ ꢃ ꢃHN(2)
d (1H)/ppm
form (e = 4.9) solution using IEF-PCM model (for comparison with
experimental chemical shifts obtained in chloroform [44,45]) as
well as in gas phase.
Calculation of nuclear shielding of C and H atoms were carried
out using the B3LYP density functional theory on 6-311G, 6-
311++G, 6-311Gꢁꢁ basis sets. Theoretical calculations were carried
Table 1a
Selected geometrical parameters of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (1),
4-methyl-3,5-dinitro -2-(2-phenylhydrazinyl)-pyridine (2) and 6-methyl-3,5-dinitro
-2-(2-phenylhydrazinyl)pyridine (3) calculated using DFT (6-31G(d,p)a and 6-
311G(d,p)) methods.
Bond length (Å)
1
2
3
out for the compounds in chloroform (e = 4.9) solution and for the
(N2)A(N1)
1.39165a
1.39061
1.34404a
1.34318
1.42378a
1.42240
1.35802a
1.35516
1.43698a
1.43509
1.38591a
1.38257
1.38681a
1.38441
1.40290a
1.39966
1.32091a
1.31853
1. 24535a
1.23870
1.22766a
1.21990
1.39443a
1.394119
1.35146a
1.35214
1.42336a
1.42178
1.35130a
1.34743
1.43757a
1.43428
1.40931a
1.40478
1.40833a
1.40606
1.40016a
1.39601
1.31846a
1.31679
1.24393a
1.23639
1.22837a
1.22066
1.39219a
1.39087
1.34584a
1.34550
1.42352a
1.42206
1.35156a
1.34852
1.43224a
1.43023
1.38261a
1.37920
1.38883a
1.38626
1.42245a
1.41956
1.33066a
1.32864
1.24575a
1.23898
1.22792a
1.22018
isolated molecules (in gas phase). Charges (Mulliken and NPA) on
the atoms were also calculated using the B3LYP/6-311G(d,p)//6-
311Gꢁꢁ basis.
(N2)A(Cpyridine
(N1)A(Cphenyl
)
)
The calculated isotropic shielding constants
were transformed to chemical shifts relative to TMS using the
equation d(i) = (i). These calculations were accom-
r
for 13C and 1H
(Npyridine)A(C2)
(C2)A(C3)
(C3)-(C4)
r(TMS) ꢂ
r
plished on the same level of theory as other DFT calculations.
The SpinWorks 3 program was used for simulation of the 1H and
13C NMR spectra. The GaussView 4.1.2 program was used for visu-
alization both of the 1H and 13C NMR.
(C4)A(C5)
(C5)A(C6)
3. Results and discussion
(C6)A(Npyridine
(N)A(O)HB
(N)A(O)
)
3.1. Structure
Structures of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, 4-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
and
6-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (Fig. 1a–c) are
determined by two (pyridine and phenyl) rings and the NHANH
bridge between them. Selected structural data are given in
Table 1a.
N(2)AN(1) and CpyridineAN bond lengths (1.390 Å and about
1.35 Å respectively) are relatively low and suggest a coupling of
2.2. NMR spectra
13C NMR spectra of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 6-
the nitrogen lone electron pair of 2-NHNH-group with p-electrons
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, dissolved in
CDCl3, were recorded on a Bruker 500 spectrometer. TMS reference
agent and 2-D z-pulsed field gradient were used. 1H and 13C het-
ero-nuclear multiple bond correlation experiments (HMBC) were
performed to assess the reliability of the 13C NMR spectra.
The 1H NMR spectra were recorded at 300 K using a 300 MHz
Bruker ARX 300 spectrometer. CDCl3 was used as a solvent and
TMS as an internal standard.
of the pyridine ring. The NAN bond of NHANH bridge is almost ‘‘in
plane’’ of the pyridine ring. The bond lengths in the phenyl ring are
close to those in the molecule of unsubstituted benzene and they
are about 1.390 Å. The NACphenyl bond is relatively long: about
1.420 Å. Bond lengths in the pyridine ring differ from those in a
molecule of unsubstituted pyridine i.e. the bonds: NpyridineAC6
and NpyridineAC2 are most shortened (the lengths about 1.316 Å),
whereas the bonds C4AC3 and C4AC5 are most lengthened
(lengths about 1.400 Å).
2.3. Computational method
Different bond lengths: of NAO in 3-NO2 and of NAH in 2-
NHANH were also observed. The NAO bond is lengthened by about
0.019 in comparison with the latter NAO in OANAO; this is due to
an intramolecular hydrogen bond between the oxygen atom of the
3-NO2 group and the hydrogen atom of 2-NH group. The data of
geometry of the hydrogen bond are given in Table 1.
Calculations were based on Gaussian 03 program package [36].
The structures were optimized using the B3LYP/6-31G(d,p) and
B3LYP/6-311G(d,p) approach. Energies and dipole moments were
calculated on the same basis.

M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
19
Fig. 2. Experimental 13C NMR spectra of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (1), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (2) and 6-methyl-3,5-dinitro-
2-(2-phenylhydrazinyl)pyridine (3).
Table 2
Table 3
Experimental 13C and 1H NMR chemical shifts (d, ppm) of 3,5-dinitro-2-(2-
phenylhydrazinyl)pyridinea(1) and 2-(2-phenylhydrazinyl)pyridinea,b(2).
Experimental 13C and 1H NMR chemical shifts (d, ppm) of 4-methyl-3,5-dinitro-2-(2-
phenylhydrazinyl)pyridinea(1), 4-methyl-2-(2-phenylhydrazinyl)pyridinea,c (2) and
2-(2-phenylhydrazinyl)pyridinea,b(3).
d(1)
d(2)
(d(1) ꢂ d(2)
)
d(1)
d(2)
d(3)
(d(1) ꢂ d(2)
)
C2
C3
C4
C5
C6
C10
C20
C30
C40
C50
C60
H3
H4
H5
H6
154.14
126.68
131.67
135.61
151.26
146.95
114.24
129.56
122.5
129.56
114.24
–
160.6
106.3
138.2
120.1
147.8
148.2
112.4
129.3
115.2
129.3
112.4
ꢂ6.46
20.38
ꢂ6.53
15.51
3.46
ꢂ1.25
1.84
0.26
7.3
C2
C3
C4
C5
C6
C10
C20
C30
C40
C50
C60
153.03
131.55
141.02
138.97
148.84
147.21
113.89
129.49
122.18
129.49
113.89
16.16
160.7
106.5
149.4
116.7
147.4
148.4
112.3
129.2
120.0
129.2
112.3
21.2
160.6
106.3
138.2
120.1
147.8
148.2
112.4
129.3
115.2
129.3
112.4
–
ꢂ6.67
25.05
ꢂ7.38
22.27
1.44
ꢂ1.19
1.59
0.29
2.18
0.29
1.59
ꢂ5.04
–
–
–
0.26
1.84
–
6.75
9.22
–
9.27
10
7.45
6.80
8.10
6.30
1.77
–
1.17
3.70
CH3
H3
H4
H5
H6
–
–
–
8.9
8.19
6.64
–
6.52
7.95
6.8
6.75
7.45
6.80
8.10
6.30
N(2)HAN(1)H
6.79
5.87
0.92
0.95
1.39
N(2)HAN(1)H
H20
H30
H40
H50
H60
6.93
7.26
6.98
7.26
6.93
6.76
7.20
6.65
7.20
6.76
0.17
0.06
0.33
0.06
0.17
N(2)HAN(1)H
6.34
5.9
5.87
0.44
N(2)HAN(1)H
H20
H30
H40
H50
H60
6.87
7.24
6.95
7.24
6.87
2.64
6.8–6.9
7.1–.3
6.8–6.9
7.1–7.3
6.8–6.9
2.20
6.76
7.20
6.65
7.20
6.76
–
0.07–0.03
0.14–(ꢂ0.06)
0.15–0.05
0.14–0.06
0.07–0.03
0.44
a
Recorded in CDCl3.
Ref. [12].
b
CH3
a
b
c
Recorded in CDCl3.
Ref. [45].
Ref. [12].
All three compounds studied are polar, showing relatively large
dipole moments of 4.30D, 2.32D and 4.45D for 3,5-dinitro-2-
(2-phenylhydrazinyl)pyridine and its 4-methyl and 6-methyl
derivatives, respectively. The methyl substitution in position 4 of
the pyridine ring significantly reduces the polarity.
upon changing the basis 6-31G for 6-311G for the molecules
studied).
Vibrational frequencies of the molecules studied were calcu-
lated using 6-31G(d,p)//6-31G(d,p) and 6-311G(d,p)//6-311G(d,p)
bases and no negative value for any frequency was encountered.
Thus the reality of optimized structures has been confirmed.
Total Energies and Z-Point Vibration Energies (ZPVE), computed
in basis set 6-31G(d,p)//6-31G(d,p) and 6-311G(d,p)//6-311G(d,p),
are as follows (Table 1b): 141.101 kcal/mol and 130.917 kcal/mol,
140.431 kcal/mol and 130.21191 kcal/mol, respectively, for 3,5-di-
3.2. 13C NMR
The 13C NMR spectra are presented in Fig. 2. Experimental val-
ues of chemical shifts are summarized in Tables 2–4 and compared
with literature data for not nitrated compounds i.e. 4-methyl-2-(2-
phenylhydrazinyl)pyridine and 6-methyl-2-(2-phenylhydrazi-
nyl)pyridine and for 2-(2-phenylhydrazinyl)pyridine itself. Those
values for pyridine ring carbons decrease in the following se-
quences: C2 > C6 > C5 > C4 > C3, C2 > C6 > C4 > C5 > C3 and
C6 > C2 > C5 > C4 > C3 for 3,5-dintro-2-(2-phenylhydrazinyl)pyri-
dine and for its 4-methyl and 6-methyl derivative, respectively.
Least shielded carbon atoms: C2 or C6 are situated between the
nitro-2-(2-phenylhydrazinyl)pyridine,
159.616 kcal/mol
and
148.51326 kcal/mol, 158.911 kcal/mol and 147.76537 kcal/mol
for 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and
159.411 kcal/mol and 147.76537 kcal/mol, 158.626 kcal/mol and
147,37167 kcal/mol for 6-methyl-3,5-dinitro-2-(2-phenylhydrazi-
nyl)pyridine (an energy decrease by about 1 kcal/mol is observed

20
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
Table 4
Experimental 13C and 1H NMR chemical shifts (d, ppm) of 6-methyl-3,5-dinitro-2-(2-
phenylhydrazinyl)pyridinea (1), 6-methyl-2-(2-phenylhydrazinyl)pyridinea,c (2) and
2-(2-phenylhydrazinyl)pyridinea,b (3).
d(1)
d(2)
d(3)
(d(1)-d(2))
C2
C3
C4
C5
C6
C10
C20
C30
C40
C50
C60
151.72
125.44
131.67
136.0
162.38
147.36
114.24
129.48
122.37
129.48
114.24
25.83
160.0
102.9
138.5
114.7
156.8
148.1
112.2
129.2
120.0
129.2
112.2
24.0
160.6
106.3
138.2
120.1
147.8
148.2
112.4
129.3
115.2
129.3
112.4
–
ꢂ8.28
22.54
ꢂ6.83
21.30
5.58
ꢂ0.64
2.04
0.28
2.37
0.28
2.04
1.83
CH3
H3
H4
H5
H6
–
9.23
–
–
9.9
6.58/6.59
7.37
6.58/6.59
–
6.75
7.45
6.80
8.10
6.30
–
1.86
–
–
3.5
6.4
N(2)HAN(1)H
6.85
5.8
5.87
1.05
N(2)HAN(1)H
H20
H30
H40
H50
H60
6.97
7.27
6.94
7.27
6.97
2.8
6.8–6.9
7.1–7.3
6.8–6.9
7.1–7.3
6.8–6.9
2.4
6.76
7.20
6.65
7.20
6.76
–
0.17–(0.07)
0.17–(ꢂ0.03)
0.14–0.04
0.17–(ꢂ0.03)
0.17–0.07
0.04
CH3
a
b
c
Recorded in CDCl3.
Ref. [45].
Ref. [12].
Table 5
Effects of methyl groups on 13C NMR resonances in 4-methyl- and 6-methyl-3,5-
dinitro-2-(2-phenylhydrazinyl)pyridine.
Carbons
(d(1) ꢂ d(2))a/ppm
(d(3) ꢂ d(2))a/ppm
C2
C3
C4
C5
C6
C10
C20
C30
C40
C50
C60
ꢂ1.11
ꢂ2.42
ꢂ1.24
0.0
0.39
11.12
0.41
4.87
9.35
3.36
ꢂ2.42
0.26
ꢂ0.35
ꢂ0.07
ꢂ0.32
ꢂ0.07
ꢂ0.35
0.0
ꢂ0.08
ꢂ0.013
ꢂ0.08
0.0
a
(1) 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
(2) 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
(3) 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl) pyridine.
Fig. 3. (a) Experimental 1H NMR spectra of 3,5-dinitro-2-(2-phenylhydrazinyl)
pyridine. (b) Experimental 1H NMR spectra of 4-methyl-3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine. (c) Experimental 1H NMR spectra of 6-methyl-3,5-dinitro-2-
(2-phenylhydrazinyl)pyridine.
pyridine nitrogen and an electron-withdrawing NO2 group. Shield-
ing of C3 carbon in all compounds studied is the greatest shielding
among carbons in the pyridine ring; comparing the C3 chemical
shifts in those three compounds, the lowest one can be found for
the 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine. Chemi-
cal shifts of carbons in the phenyl ring of the three compounds
respectively. According to the literature [47], carbon resonance
for methyl groups in 4-methyl-2-(2-phenylhydrazinyl)pyridine is
at 21.2 ppm and in 6-methyl-2-(2-phenylhydrazinyl)pyridine at
24.0 ppm. The unexpected shift (by about 5 ppm) of resonance line
towards higher fields for 4 methyl derivative can be explained as a
result of increased steric interaction between the methyl group
and two neighboring nitro groups: 3-NO2 and 5-NO2.
As it results from the comparison of experimental chemical
shifts of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, 4-methyl-
3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 6-methyl-3,5-di-
nitro-2-(2-phenylhydrazinyl)pyridine with those of their counter-
parts without nitro groups, the largest differences can be
observed for carbons C5 and C3; they are in the range of 15–
22 ppm and of 20–25 ppm, respectively (Tables 2–4). This is
investigated show
a similar pattern decreasing as follows:
C10 > C30@C50 > C40 > C20@C60. The carbon atom in position 2 (ortho
to the NH substituent) is most shielded, followed by carbon in the
position 4 (para to the NH), which can be explained by a coupling
of lone electron pair of nitrogen of the NH group with the
p elec-
tron sextet of the phenyl ring. Similar shifts pattern was observed
in aminobenzene where according to literature [46] the shifts were
as follows: 146,7(C1), 129,3 (C3, C5), 118,5(C4) and 115,1 (C2, C6).
The chemical shift of the methyl group is 16.16 and 25.83 ppm
for the 4-methyl derivative and the 6-methyl derivative,

M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
21
ꢂ7 ppm, which means that these carbons are more shielded. How-
ever, resonance lines of carbon C6 are shifted towards lower fields
(the differences in chemical shifts of up to 5 ppm).
To demonstrate the effect of methyl groups on carbon reso-
nances of the compounds tested, differences of corresponding
chemical shifts of carbons in the respective pairs of compounds:
4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 3,5-di-
nitro-2-(2-phenylhydrazinyl)pyridine, and 6-methyl-3,5-dinitro-
2-(2-phenylhydrazinyl)pyridine and 3,5-dinitro-2-(2-phenylhydr-
azinyl)pyridine, have been calculated. The results are summarized
in Table 5. Greatest changes are observed for the ipso carbons (di-
rectly bound to the methyl group); they reach 11 ppm.
3.3. 1H NMR
The spectra of compounds studied are presented in Fig. 3a–c.
Experimental spectral data are summarized in Tables 2–4. The pyr-
idine ring only embodies H4 and H6 protons or H6 or H4 protons
for molecules of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, 4-
Fig. 4. Experimental 1H NMR chemical shifts vs. experimental 13C NMR chemical
shifts for 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (1), 4-methyl-3,5-dinitro-2-
(2-phenylhydrazinyl)pyridine (2) and 6-methyl-3,5-dinitro-2-(2-phenylhydrazi-
nyl)pyridine (3).
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
and
6-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, respectively.
H4 proton resonances are in relatively very low fields (the
chemical shifts are about 9.2 ppm for two molecules studied). This
can be explained by the effect of two ortho-nitro groups: 3-NO2
and 5-NO2. For mono substituted 3-nitro pyridine, Badgujar et al.
[2] found a resonance of H4 at 8.99 ppm. The proton resonances
consistent with electron withdrawing properties of the nitro
groups. The presence of nitro groups in the pyridine ring also af-
fects the resonances of C2 and C4 carbons (ortho to 3-nitro and
5-nitro groups), for which the chemical shift differences are about
Table 6
Calculated and experimental 13C and 1H NMR chemical shifts (ppm) of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
6-31G(d,p)//6-311G
6-31G(d,p)//6-311++G
6-311G(d,p)//6-311G
6-311G(d,p)//6311++G
6-311G(d,p)//6311Gꢁꢁ
EXP
C2
155.01
155.67
134.20
135.89
135.48
136.33
142.67
144.28
156.34
157.56
153.66
154.09
116.54
116.82
136.10
136.14
129.03
128.94
135.80
136.05
120.30
120.74
9.32
155.75
156.49
134.48
136.42
136.82
137.89
142.61
144.38
157.32
158.75
154.63
155.09
117.60
117.96
136.57
136.58
129.00
128.89
136.55
136.78
120.87
121.37
9.52
153.91
154.55
134.78
136.43
134.77
135.54
143.05
144.64
155.57
156.72
153.23
153.65
116.32
116.59
135.91
135.95
128.80
128.72
135.59
135.83
120.19
120.63
9.28
154.65
155.37
135.02
136.92
136.14
137.12
143.03
144.77
156.54
157.89
154.12
154.57
117.49
117.86
136.46
136.46
128.82
128.71
136.38
136.62
120.75
121.25
9.07
156.75
157.36
132.66
134.00
137.38
138.08
141.58
142.71
157.79
159.01
154.09
154.56
115.26
115.51
135.68
135.70
127.69
127.55
135.33
135.56
119.36
119.84
9.32
154.14
C2a
C3
126.68
131.67
135.61
151.26
146.95
114.24
129.56
122.5
129.56
114.24
9.22
C3a
C4
C4a
C5
C5a
C6
C6a
C10
a
C10
C20
C20
C30
C30
C40
C40
C50
C50
C60
C60
H4
a
a
a
a
a
H4a
H6
9.43
9.44
9.63
9.65
9.59
9.80
9.39
9.42
9.60
9.20
9.15
9.36
9.43
9.27
9.43
9.27
H6a
9.98
10.01
9.84
9.46
10.17
10
N(2)HAN(1)H
N(2)HAN(1)Ha
N(2)HAN(1)H
10.13
6.92
7.41
10.17
7.31
7.83
10.00
7.07
7.51
9.64
7.03
7.51
10.30
7.18
7.60
6.79
N(2)HAN(1)Ha
H20
6.79
6.93
7.31
7.52
7.02
7.21
7.02
7.56
6.81
7.11
6.90
7.05
7.32
7.54
7.02
7.23
7.21
7.45
6.95
7.28
6.81
6.94
7.33
7.53
7.02
7.21
7.34
7.57
6.82
7.12
6.53
6.69
6.93
7.15
6.65
6.85
6.81
7.04
6.56
6.88
7.04
7.16
7.48
7.66
7.14
7.31
7.48
7.68
7.03
7.30
6.93
7.26
6.98
7.26
6.93
a
H20
H30
a
H30
H40
a
H40
H50
a
H50
H60
a
H60
a
In chloroform.

22
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
Table 7
Calculated and experimental 13C and 1H NMR chemical shifts (ppm) of 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
6-31G(d,p)//6-311G
6-31G(d,p)//6-311++G
6-311G(d,p)//6-311G
6-311G(d,p)//6-311++G
6-311G(d,p)//6-311Gꢁꢁ
EXP
C2
157.40
158.01
138.03
139.35
155.78
156.58
147.46
148.76
156.62
157.68
154.81
155.28
116.91
117.17
135.76
135.84
128.33
128.20
135.59
135.86
119.98
120.33
22.90
158.24
158.95
139.30
140.80
157.15
158.16
148.13
149.56
157.51
158.75
156.12
156.62
117.93
118.30
136.23
136.29
127.64
127.48
136.51
136.80
119.99
120.41
23.28
156.34
156.96
138.73
139.96
154.14
154.91
148.14
149.38
155.60
156.65
154.62
155.07
116.77
117.03
135.52
135.60
128.00
127.88
135.35
135.61
119.74
120.09
22.36
157.16
157.87
140.07
141.47
155.49
156.45
148.87
150.23
156.51
157.74
155.73
156.20
117.84
118.22
135.94
136.01
127.37
127.21
136.30
136.58
119.78
120.18
22.74
158.83
159.48
136.58
137.53
155.13
155.86
146.43
147.29
157.58
158.70
155.48
155.98
115.70
115.94
135.33
135.38
126.96
126.78
135.04
135.29
118.96
119.35
21.79
153.03
C2a
C3
131.55
141.02
138.97
148.84
147.21
113.89
129.49
122.18
129.49
113.89
16.16
C3a
C4
C4a
C5
C5a
C6
C6a
C10
a
C10
C20
C20
C30
C30
C40
C40
C50
C50
C60
C60
a
a
a
a
a
CH3
a
22.82
23.26
22.25
22.68
21.66
CH3
H6
9.28
9.44
9.51
9.45
9.64
9.56
9.22
9.39
9.17
8.99
9.18
8.83
9.01
9.22
9.45
8.9
H6a
8.19
N(2)HAN(1)H
N(2)HAN(1)Ha
N(2)HAN(1)H
9.67
6.38
6.89
9.73
6.82
7.36
9.35
6.47
6.92
9.02
6.48
6.95
9.61
6.59
7.01
6.34
N(2)HAN(1)Ha
H20
6.67
6.82
7.23
7.43
6.91
7.11
7.27
7.49
6.78
7.09
3.44
3.37
2.48
2.55
2.73
2.72
6.79
6.95
7.14
7.36
6.93
7.13
7.02
7.25
6.87
7.20
3.53
3.47
2.59
2.66
2.86
2.86
6.70
6.86
7.23
7.44
6.91
7.10
7.28
7.50
6.78
7.08
3.43
3.36
2.40
2.47
2.64
2.64
6.41
6.59
6.74
6.96
6.53
6.73
6.61
6.84
6.48
6.80
3.11
3.04
2.10
2.17
2.35
2.35
6.92
7.06
7.39
7.57
7.04
7.21
7.41
7.61
6.99
7.26
3.06
3.02
2.34
2.41
2.57
2.57
6.87
7.24
6.95
7.24
6.87
2.64
a
H20
H30
a
H30
H40
a
H40
H50
a
H50
H60
a
H60
1H(CH3)
1H(CH3)a
2H(CH3)
2H(CH3)a
3H(CH3)
3H(CH3)a
a
In chloroform.
of H6 in 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 4-methyl-
3,5-dinitro-2-(2-phenylhydrazinyl)pyridine are observed at 9.27
and 8.90 ppm, respectively.
Chemical shifts for protons of the phenyl ring are similar for all
tested compounds. The sequences of resonances towards increas-
ing fields are as follows: H30@H50 > H40 > H20@H60 for 3,5-dinitro-
2-(2-phenylhydrazinyl)pyridine and 4-methyl derivative but
H30@H50 > H20@H60 > H40 for 6-methyl derivative.
A notable effect of nitro groups in the pyridine ring can be ob-
served not only for proton of NH adjacent to this ring but also of
the latter NH (bound to the phenyl ring). Oniciu et al. [12] found
resonances for the former and the latter NH in unsubstituted 2-
(2-phenylhydrazinyl)pyridine dissolved in CDCl3 at 6.30 and
5.87 ppm, respectively.
3.4. Correlation between experimental 1H and 13C chemical shifts
For hydrazino group: (pyridine)AN(1)HAN(2)HA(benzene) the
following pairs of resonances have been observed (ppm): 10.0
and 6.79, 8.19 and 6.34 and 9.9 and 6.85 for 3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine and for its 4-methyl- and 6-methyl-deriva-
tives, respectively. The shifts for protons of NH adjacent to the
pyridine ring are much higher which obviously results from the
vicinity of two nitro groups and the presence of intramolecular
hydrogen bond with oxygen of 3-NO2 group. The lowered (by
about 2 ppm) chemical shift for 4-methyl-3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine as compared to the other compounds is
due to the presence of methyl group in position 4 as a steric
hindrance.
In Fig. 4, correlations between experimental chemical shifts of
hydrogen and carbon atoms for all three compounds studied have
been presented. The best correlation has been obtained for 4-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (the correla-
tion coefficient R2 = 0.9802).
3.5. Results of theoretical calculations
3.5.1. Shielding constants
In Tables 6–8, chemical shifts of carbon and hydrogen atoms,
calculated in a variety of bases excluding or including the impact

M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
23
Table 8
Calculated and experimental 13C and 1H NMR chemical shifts (ppm) of 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
6-31G(d,p)//6-311G
6-31G(d,p)//6-311++G
6-311G(d,p)//6-311G
6-311G(d,p)//6-311++G
6-311G(d,p)//6-311Gꢁꢁ
EXP
C2
153.32
153.91
133.74
135.36
138.00
138.53
142.97
144.47
171.11
171.92
154.19
154.56
116.82
117.03
136.11
136.00
128.76
128.73
135.70
136.00
120.13
120.61
32.20
153.77
154.44
134.21
136.06
138.96
139.72
143.28
144.97
172.70
173.73
155.01
155.40
117.69
117.98
136.45
136.44
128.63
128.60
136.24
136.53
120.73
121.30
31.98
152.71
153.27
134.30
135.86
137.20
137.67
143.47
144.94
170.36
171.11
153.89
154.26
116.57
116.77
135.92
135.94
128.49
128.45
135.49
135.79
119.89
120.37
32.08
153.16
153.79
134.752
136.54
138.17
138.86
143.81
145.48
171.94
172.91
154.72
155.11
117.48
117.76
136.26
136.24
128.36
128.32
136.08
136.36
120.48
121.04
31.84
155.48
157.05
132.13
133.28
140.09
141.78
141.56
142.54
171.89
174.00
154.74
155.82
115.49
116.33
135.68
136.28
127.41
128.02
135.23
136.13
119.07
120.24
31.31
151.72
C2a
C3
125.43
131.67
135.99
162.38
147.36
114.24
129.47
122.36
129.47
114.24
25.83
C3a
C4
C4a
C5
C5a
C6
C6a
C10
a
C10
C20
C20
C30
C30
C40
C40
C50
C50
C60
C60
a
a
a
a
a
CH3
CH3
H4
a
32.21
9.53
9.57
32.02
9.74
9.79
32.06
9.49
9.52
31.87
9.29
9.34
31.83
9.55
9.67
9.23
H4a
9.83
9.86
9.70
9.31
10.02
9.9
N(2)HAN(1)H
N(2)HAN(1)Ha
N(2)HAN(1)H
9.97
6.78
7.18
10.02
7.17
7.59
9.85
6.79
7.17
9.48
6.78
7.18
10.35
6.94
7.34
6.85
N(2)HAN(1)Ha
H20
6.79
6.92
7.30
7.51
7.00
7.20
7.33
7.57
6.80
7.11
3.36
3.32
3.39
3.37
2.56
2.62
6.94
7.09
7.34
7.56
6.95
7.16
7.25
7.49
6.90
7.24
3.39
3.37
3.45
3.43
2.62
2.69
6.80
6.93
7.31
7.52
7.00
7.20
7.34
7.57
6.80
7.11
3.34
3.31
3.40
3.38
2.55
2.62
6.54
6.69
6.94
7.16
6.55
6.76
6.84
7.08
6.49
6.83
2.97
2.94
3.05
3.03
2.20
2.28
7.02
7.19
7.46
7.69
7.12
7.36
7.47
7.73
7.02
7.36
3.14
3.18
3.21
3.24
2.42
2.55
6.97
7.27
6.94
7.27
6.97
2.8
a
H20
H30
a
H30
H40
a
H40
H50
a
H50
H60
a
H60
1H(CH3)
1H(CH3)a
2H(CH3)
2H(CH3)a
3H(CH3)
3H(CH3)a
a
In chloroform.
of the solvent (CHCl3,
e
= 4.9), have been given. Correlations be-
3.5.2. NPA (Natural Populations Analysis) and Mulliken charges
tween experimental chemical shifts of particular atoms and calcu-
lated shielding constants are represented by Figs. 5 and 6.
Calculations were carried out in the system databases 6-
311G(d,p)//6-311Gꢁꢁ. The results (charge values) are given in Ta-
bles 9 and 10 and presented as correlations with the experimental
chemical shifts of carbon and hydrogen atoms (Figs. 7 and 8,
respectively).
Best results were obtained for 6-methyl-3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine where correlation coefficients R2 for carbons
are greater than 0.99. For two other compounds tested R2 ranges
from 0.96 to 0.98. Of the five possible options for database sys-
tems: 6-31G(d,p)//6-311G, 6-31G(d,p)//6-311++G, 6-311G(d,p)//
6-311G, 6-311G(d,p)//6-311++G and 6-311G(d,p)//6-311Gꢁꢁ, the
The best correlation results were found for charges com-
puted by NPA method for carbon atoms, however R2 is not
greater than 0.86. For hydrogen atoms,
a better correlation
best results were mostly obtained for the 6-311G(d,p)//6-311Gꢁꢁ
.
has been obtained for Mulliken charges (R2 of about 0.50 at a
maximum).
Calculations were performed in two versions: with and without
taking into account CHCl3 as a solvent; no significant changes were
observed in correlation diagrams.
For 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine, NPA charges of
atoms
H4 > H6 > H20 > H60 > H40 > H50 > H30, C2 > C6 > C3 > C5 > C4, C10 >
C3 > C50 > C40 > C60 > C20.
Whereas, those sequences are:
decrease
in
the
following
sequences:
For hydrogen atoms, best results of the correlation (R2 above
0.99) have been also obtained for 6-methyl-3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine but similarly for 3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine too. For different variants of calculations,
the base 6-311G(d,p)//6-311Gꢁꢁ proved to be the best one in most
cases.
H6 > H20 > H40 > H60 > H50 > H30, C2 > C6 > C4 > C3 > C5, C10 > C30 >
C50 > C40 > C60 > C20 for 4-methyl derivative and H4 > H20 > H40 >
H60 > H30 > H50, C2 > C6 > C3 > C5 > C4, C10 > C30 > C50 > C40 > C60
> C20 for 6-methyl derivative.

24
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
Fig. 5. Plots of experimental 13C chemical shifts vs. calculated/(1) 6-31G(d,p)//6-311G, (2) 6-31G(d,p)//6-311++G/, (3) 6-311G(d,p)//6-311G, (4) 6-311G(d,p)//6-311++G, (5)
6-311G(d,p)//6-311Gꢁꢁ/ absolute shielding constants for 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (3,5DN2PHP), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
(4M3,5DN2PHP) and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (6M3,5DN2PHP); (upper plots
chloroform).
– for isolated molecules; lower plots – for molecules in
Fig. 6. Plots of experimental 1H chemical shifts vs. calculated/(1) 6-31G(d,p)//6-311G, (2) 6-31G(d,p)//6-311++G,/(3) 6-311G(d,p)//6-311G, (4) 6-311G(d,p)//6-311++G, (5) 6-
311G(d,p)//6-311Gꢁꢁ
absolute shielding constants for 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (3,5DN2PHP), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
/
(4M3,5DN2PHP) and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (6M3,5DN2PHP); (upper plots
chloroform).
– for isolated molecules; lower plots – for molecules in

M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
25
Table 9
Natural charges (NPA) and Mulliken charges (M) for carbons in 3,5-dinitro-2-(2-phenyl-hydrazinyl)pyridine(1), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine(2) and 6-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine(3).
(1)/NPA
(1)/M
0.469687
0.045580
0.082398
0.001385
0.149983
(2)/NPA
(2)/M
0.487006
0.016435
0.103130
(3)/NPA
(3)/M
0.480747
0.038148
0.084146
0.038833
0.154461
C-2
C-3
C-4
C-5
C-6
C-10
C-20
C-30
C-40
C-50
C-60
0.41763
ꢂ0.01131
ꢂ0.11322
ꢂ0.02331
0.143309
0.16467
0.42595
ꢂ0.01198
0.08129
0.42897
ꢂ0.01714
ꢂ0.10831
ꢂ0.02340
0.32343
ꢂ0.01911
ꢂ0.018322
0.14167
0.161875
0.121713
0.16967
0.124569
0.16686
0.122788
ꢂ0.25789
ꢂ0.17167
ꢂ0.22355
ꢂ0.17565
ꢂ0.23759
ꢂ0.066534
ꢂ0.098796
ꢂ0.090676
ꢂ0.096481
ꢂ0.085866
ꢂ0.25628
ꢂ0.17293
ꢂ0.22659
ꢂ0.17636
ꢂ0.24057
ꢂ0.060557
ꢂ0.097844
ꢂ0.092894
ꢂ0.097383
ꢂ0.090886
ꢂ0.25719
ꢂ0.17199
ꢂ0.22498
ꢂ0.17618
ꢂ0.23958
ꢂ0.064932
ꢂ0.098650
ꢂ0.091647
ꢂ0.096913
ꢂ0.089167
Table 10
shifts (Tables 1–4). In that group, an increased positive charge is
on hydrogen bound by the intramolecular hydrogen bond with
oxygen of the 3-NO2 group (in comparison with the latter hydro-
gen), thus that proton is more deshielded giving resonances in low-
er fields. Amongst the compounds studied, the highest positive
charge on hydrogen of N(1)HAN(2)H has been found for 3,5-dini-
tro-2-(2-phenylhydrazinyl)pyridine and the lowest for 4-methyl-
3,5-dinitro-2-(2-phenylhydrazinyl)pyridine.
Natural charges (NPA) and Mulliken charges (M) for protons in 3,5-dinitro-2-(2-
phenyl-hydrazinyl)pyridine(1), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyri-
dine(2) and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine(3).
(1)/NPA
(1)/M
(2)/NPA
(2)/M
(3)/NPA
(3)/M
H-4
H-6
H-20
H-30
H-40
H-50
H-60
0.27515
0.22185
0.20908
0.20343
0.20389
0.20358
0.20453
0.175641
0.160484
0.096023
0.099497
0.096166
0.098877
0.097855
–
–
0.27676
–
0.176490
–
0.21953
0.20852
0.20220
0.20281
0.20243
0.20265
0.156971
0.092116
0.097430
0.094019
0.096794
0.094636
0.20958
0.20303
0.20346
0.20297
0.20331
0.095913
0.098895
0.095315
0.097820
0.095796
The Mulliken charges for 3,5-dinitro-2-(2-phenylhydrazi-
nyl)pyridine
decrease
as
follows:
H4 > H6 > H30 > H50 >
H60 > H40 > H20, C2 > C6 > C4 > C3 > C5, C10 > C20 > C60 > C40 > C50 >
C30. Whereas, the sequences are: H6 > H30 > H50 > H60 > H40 > H20,
C2 > C6 > C4 > C3 > C5, C10 > C20 > C60 > C40 > C50 > C30 for 4-methyl
derivative and H4 > H30 > H50 > H20 > H60 > H40, C2 > C6 > C4 > C5 >
C3, C10 > C20 > C60 > C40 > C50 > C30 for 6-methyl derivative. Mullik-
en charges of protons of phenyl ring are notably lower than those
of protons of pyridine ring.
NPA charges of C5 and C4 atoms correlate very well with chem-
ical shifts for all compounds studied; a higher value of chemical
shift corresponds to a higher positive charge on C5 (greater desh-
ielding) as compared with C4. However, NPA charges on the atoms
C2 and C6 correlate well with the experimental chemical shifts for
molecules of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine and 4-
methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine only.
With regard to carbon atoms, the charges on C2 and C6 corre-
late very well with chemical shifts for 3,5-dinitro-2-(2-phen-
ylhydrazinyl)pyridine and its 4-methyl derivative;
a more
NPA charges on carbons of phenyl ring correlate well with
chemical shifts. The most positive charge for C10 corresponds to
the highest value of chemical shift of about 147 ppm. Only for
the pairs of carbons C30 and C50 and C60 and C20, calculated values
of NPA charges are different, whereas experimental chemical shift
are identical; this can be explained by the rotation of the benzene
ring, resulting in a mean resonance signal observed.
The calculated NPA charges of nitrogen and hydrogen atoms in
hydrazino group AN(1)HAN(2)HA as well as of oxygen atoms in 3-
NO2 correlate very well with experimental values of chemical
positive charge on C2 corresponds to a resonance in the lower field
(C2 is more deshielded than C6). Also Mulliken charges on C4 and
C3 atoms correlate well with chemical shifts for all three com-
pounds studied; the more ‘‘positive’’ C4 shows a resonance in a
lower field than C3.
As regards 1H NMR resonances, only Mulliken charges of some
hydrogen atoms show relatively good correlations with chemical
shifts. For example, in 6-methyl-3,5-dinitro-2-(2-phenylhydrazi-
nyl)pyridine, more ‘‘positive’’ H4 is clearly more deshielded (chem-
ical shift 9.24 ppm) than less ‘‘positive’’ H20 or H60 (chemical shifts
Fig. 7. Plots of calculated NPA and Mulliken (M) charges/6-311G(d,p)//6-311Gꢁꢁ/ vs. experimental chemical shifts for carbon atoms of 3,5-dinitro-2-(2-phenylhydraz-
inyl)pyridine
(3,5DN2PHP),
4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
(4M3,5DN2PHP)
and
6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
(6M3,5DN2PHP).

26
M. Wandas, Z. Talik / Journal of Molecular Structure 1043 (2013) 15–27
Fig. 8. Plots of calculated NPA and Mulliken (M) charges/6-311G(d,p)//6-311Gꢁꢁ/ vs. experimental chemical shifts for protons of 3,5-dinitro-2-(2-phenylhydrazinyl)pyridine
(3,5DN2PHP), 4-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (4M3,5DN2PHP) and 6-methyl-3,5-dinitro-2-(2-phenylhydrazinyl)pyridine (6M3,5DN2PHP).
6.97 ppm). However, general correlations between the NPA and
Mulliken charges and chemical shifts for protons in the compounds
studied are poor.
nitrogen lone electron pair with p-electrons of the pyridine ring.
All three compounds are clearly polar, however the methyl substi-
tution in position 4 of the pyridine ring significantly reduces the
polarity.
4. Conclusions
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Three pyridine compounds, i.e.: 3,5-dinitro-2-(2-phenylhydrazinyl)
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