1H and 13C NMR Study of N-(3-pyridinyl)-2-pyridinecarboxamide and N,N′-bis(2-pyridinyl)-1,3-benzenedicarboxamide

Full text of DOI:10.1016/S1386-1425(97)00046-2

Spectrochimica Acta Part A 53 (1997) 1459–1462
Short Note
1
13
H and C NMR Study of
N-(3-pyridinyl)-2-pyridinecarboxamide and
N,N%-bis(2-pyridinyl)-1,3-benzenedicarboxamide
Netai C. Singha, Jayashree Anand, D.N. Sathyanarayana *
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 27 September 1996; accepted 21 January 1997
Keywords: NMR spectroscopy; NOE; Conformation; N-(3-pyridinyl)-2-pyridinecarboxamide; N,N%-bis(2-pyridinyl)-
1,3-benzene-dicarboxamide
1. Introduction
NaHCO was added to it with stirring and was kept
3
overnight. The product was washed with water,
recrystallized from ethanol and dried in air (m.p.
118°, yield 20%).
Compound (2): A mixture of 1,3-benzenedicar-
boxylic acid chloride (2.5 g) containing 1,3-ben-
zenedicarboxylicacid and 2-aminopyridine (3 g) was
heated at 180°C for 1 h. It was cooled and treated
with excess of saturated aqueous solution of
N-(pyridinyl)carboxamides can theoretically ex-
ist in different tautomeric and rotameric structures.
In this context and in continuation of our previous
studies on pyridinecarboxamides [1,2], a study of
1
13
conformation by H and C NMR spectra of
N-(2-pyridinyl)3-pyridinecarboxamide (1) and
N,N%-bis(2-pyridinyl)-1,3-benzenedicarboxamide
NaHCO and was kept overnight. The product
(
2) (Fig. 1) is reported.
3
obtained was filtered, washed with water and
recrystallized from ethanol (m.p. 178°C, yield 15%).
1
13
The H and C NMR spectra were measured on
2
. Experimental
13
Bruker AC (270 MHz) ( C: 67.89 MHz) spectrom-
eter in CDCl , CD CN and (CD ) CO solutions
3
3
3 2
Compound (1): A mixture of 3-pyridinecar-
using Me Si as an internal calibrant. Steady state
4
boxylicacid (8.6 g) and 2-pyridylamine (4.7 g) was
heated in an oil bath at 180°C for 4 h. The hot
reaction mixture was poured with stirring to 200 ml
of water. Excess of saturated aqueous solution of
1
D NOE experiments were carried out on degassed
13
samples in CDCl . The COSY spectra, C spectra
3
in coupled and decoupled mode and HETCOSY
1
spectra were all recorded in CDCl . H and proton
3
13
coupled C NMR spectra were simulated using the
program LAOCOON-5 [3].
*
Corresponding author. Tel: +91 80 3092382; fax: +91 80
3
341683.
1
386-1425/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved.
PII S1386-1425(97)00046-2

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N.C. Singha et al. / Spectrochimica Acta Part A 53 (1997) 1459–1462
3. Results and discussion
In concentrated solution, the N –H proton
shows high frequency shifts by 1.26 ppm com-
pared with that in dilute solution (Table 1) sug-
gesting intermolecular association through
hydrogen bonding. The ring protons experience
low frequency shifts in concentrated solution
compared to those in dilute solution. In dilute
solution (about 1 mg ml ), NOEs were observed
when the NH proton was saturated at H2 (3.3%)
and H4 (2.1%), while in the concentrated solution,
the NOEs were observed at H3% (1.0%), H6%
(2.3%) and H6 (0.6%) in addition to that at H2
(6.1%) and H4 (3.3%). To use the method de-
scribed by Bell and Saunders [6] to obtain infor-
mation on distances, it is necessary that the
important relaxation process should be dipolar. In
the case of (1), the aromatic protons will also
relax by spin rotation because of the rapid rota-
tion about the C –C bond. Hence distance infor-
mation could not be reliably obtained.
The chemical shift assignments for (1) and (2)
as verified by COSY experiments and literature
data for related systems are presented in Table 1
and the COSY spectrum of (2) in CDCl is shown
3
in Fig. 2. The spectra were also simulated in good
agreement with the experimental spectra.
Very recently Katritzky and Ghiviriga [4] utiliz-
ing the technique of SIMPLE have shown that
N-(2-pyridyl)acetamide (2NPA) and N-(2-
pyridyl)benzamide (2NPB) in CDCl3 and
−
1
(
CD ) CO exist in the following tautomeric-ro-
3 2
tamer form
R =CH 2NPA
3
R =C H 2NPB
6
5
In this rotamer, H3 experiences strong deshielding
l value 8.29 ppm for 2NPA) from the carbonyl
(
A dimer structure (Fig. 3) may be proposed for
the associated species of (1) in concentrated solu-
tion to account for the concentration dependence
of the H NMR spectra and the NOEs. The N –H
proton of one molecule is hydrogen bonded to the
group compared with 6.49 ppm in 2- aminopy-
ridine and 7.29 ppm in N,N-diacetyl-2-aminopy-
ridine [5]. It has been attributed to the coplanar
proximity of the carbonyl group. A comparison of
the chemical shifts of (1) and (2) with those of
1
2
-pyridyl nitrogen of another molecule. The dis-
2NPA and 2NPB shows that for N-(2-pyridyl)-
tance of N –H proton from H3% and H6% is respec-
CONH- part of (1) and (2), a planar trans struc-
ture could be suggested. Although it is possible to
conceive other planar conformations for example
by ‘isolated molecule’ MM1 calculations, because
of the low energy barrier for rotation over the
single bond, the chemical shift of H3% clearly
supports the conformation in which H3% is closer
to the CꢀO group (see Fig. 1). This was confirmed
by the l value of 7.0 ppm for H3 of N-(2-pyridyl),
N%-(aryl)ureas [1] where the intramolecular hydro-
gen bonding renders the H3 proton to move away
from the CꢀO group as shown below. However,
the 3-pyridyl ring in (1) can undergo free rotation
about OꢀC –C3 (pyridyl) bonds because of the
low energy barrier and the chemical shifts thus
refer to the average values [1].
tively 3.89 and 4.19 A, while the observed NOE is
1
.0 and 2.3% respectively. It suggests that as a
result of association, the N –H proton comes
closer to H6% when compared with its distance in
the monomer. In the dimer, the N –H proton of
one molecule is only 3.03 A away from H6% of the
other molecule. The distances were obtained from
molecular modeling of the dimer assuming for
simplicity linear intermolecular N –H –N hydro-
Fig. 1. N-(2-pyridinyl)-3-pyridinecarboxamide (1). N,N%-bis(2-
pyridinyl)3-pyridinecarboxamide (2).

N.C. Singha et al. / Spectrochimica Acta Part A 53 (1997) 1459–1462
1461
Table 1
1
13
a
H and C Chemical shifts (in l ppm) of (1) and (2)
b
c
Compound
1)
Solvent
Group
3-py
H2, H3%
H4, H4%
H5, H5%
H6%
8.81
8.31
8.74
8.04
8.76
8.29
7.95
NH
8.67
1
(
CDCl3 (1 mg ml−
)
9.18
8.38
9.16
8.35
9.03
8.29
8.40
8.25
7.79
8.21
7.72
8.18
7.72
7.64
7.47
7.07
7.37
7.00
7.43
7.05
6.91
2
-py
3-py
-py
CDCl3 (25 mg ml−
1
)
9.86
2
3
2
2
PCA
NPA
NPB
CDCl3
CDCl3
CDCl3
3-py
2-py
2-py
10.39
10.38
(1)
(CD ) CO
3-py
9.33
8.42
9.11
8.28
8.50
7.92
8.26
7.83
7.62
7.23
7.49
7.15
8.85
8.41
8.75
8.34
9.90
9.24
3
2
2
-py
3-py
-py
CD CN
3
2
(
2)
1)
CDCl3
2-py
ph
8.39
8.59
CO/C1
7.77
8.16
C2%
7.08
7.63
C3%
8.25
8.16
C4%
9.08
C5%
C6%
(
3
CDCl3
CDCl3
3-py
3-py
164.41
170.6
148.67
152.5
130.20
129.6
135.40
137.0
123.58
124.9
152.79
148.3
PCA
2
2-py
-py
151.52
151.8
114.78
114.4
138.78
138.1
120.32
119.1
147.79
146.9
2
NPA
CDCl3
CDCl3
169.0
(2)
2-py
134.78
151.63
115.06
139.25
120.64
148.26
CDCl3
CDCl3
CDCl3
ph
2-py
ph
134.78
166.0
134.30
126.54
151.6
127.40
134.78
114.4
128.20
131.20
138.3
131.20
130.04
119.4
128.20
131.68
147.1
127.40
2
NPB
Benzamide
a
Numbering follows from Fig. 1.
b
c
2
NPA, 2NPB [4], 3PCA (N.C. Singha and D.N. Sathyanarayana, unpublished results), benzamide [7].
ph, 1,3-disubstituted phenyl group.
gen bonds and using standard N –H –N distance
3.10 A). The calculated NOE at H6% for the
relative to that of H5% (7.07 ppm) also suggests
the coplanarity of the 2-pyridyl ring with the
amide group to which it is bonded as in (1).
(
dimer is 2.8% when the N –H proton is satu-
rated, which is in satisfactory agreement with
that observed (2.3%) in the concentrated CDCl3
solution. The structure of the dimer seems to get
further support from the appearence of NOE at
H2 in the concentrated solution, when H6% was
saturated. In the monomer, H2 is 6.5 A away
from H6% and at such large distances,it is very
unlikely to observe NOE. In very dilute solu-
tions, only the monomeric form is predominant.
For (2) in CDCl when the N –H protons are
3
saturated, the NOEs are observed at H2 (7.8%)
and at H4 and H6 (2.1%) which are equivalent.
A small amount (0.5%) of NOE is also observed
at H6% and H6¦, which are equivalent. The
NOEs at H2 and H4 indicate that the distance
of NH1 proton from H4 is greater than that of
NH1 from H2. The molecular conformation of
(2) inferred from the above discussion is as
shown in Fig. 1. It finds support from the fact
that H4 and H6 are equivalent and the protons
of the ring B1 (H3% to H6%) are equivalent to the
corresponding protons of the ring B2 (H3¦ to
H6¦).
1
The H NMR spectrum of (2) was simulated
in good agreement with the experimental spec-
1
trum. H NMR spectrum in CDCl shows that
3
it exists only in one conformation. The large
down field shift (1.31 ppm) of H3% (8.38 ppm)

1
462
N.C. Singha et al. / Spectrochimica Acta Part A 53 (1997) 1459–1462
Fig. 3. Dimer structure of (1).
ring while in the diacylated compounds, it is not.
This, together with the deshielding of H3 proves
that diacylamino group adopts a less sterically
hindered conformation with the carbonyl group
out of the plane of the pyridine ring, while the
other compounds cited adopt a planar conforma-
tion.
Fig. 2. COSY contour plot of (2) in CDCl3.
1
3
The C chemical shifts of (1) and (2) (Table 1)
for the 2-pyridyl and CꢀO groups compare well
with those of 2NPA, 2NPB [2] and 3PCA (N-(3-
pyridinyl)carboxamide) (N.C. Singha and D.N.
Sathyanarayana, unpublished results) suggesting
that the conformation of the 2-pyridyl ring and
the amide group is similar in (1) and (2) consistent
References
[1] N.C. Singha and D.N. Sathyanarayana, J. Chem. Soc.
Perkin Trans. 2 (1996) in press.
[2] D.N. Sathyanarayana, S.V.K. Raja, J. Mol. Struct. 128
(
1987) 399.
[3] S. Castellano, A.A. Bothner-By, J. Chem. Phys. 41 (1964)
863.
4] A.R. Katritzky, I. Ghiviriga, J. Chem. Soc. Perkin Trans.
1
with H NMR studies. Comparison of the C3
values in (1) and (2) with those of 2-aminopy-
3
[
ridine
lamino)pyridine
(108.5
ppm),
(123.7
2-(N,N-diacety-
ppm) and
2 (1995) 1651.
[5] A. Kascheres, M. Ueno, J. Heterocycl. Chem. 28 (1991)
2
057.
2-(N,N-dibenzylamino)pyridine (121.8 ppm) [5]
[
[
6] R.A. Bell, J.K. Saunders, Can. J. Chem. 48 (1970) 1114.
indicates that in (1) and (2) as well as in 2-
aminopyridine, 2NPA and 2NPB, the lone pair on
the amino nitrogen is conjugated to the pyridine
7] V. Formacek, L. Desnoyer, H.P. Kellerhals and J.T.
13
Clerc, C Data Bank, Vol. 1, Copyright Bruker-Physik,
Karlsruhe, 1976.
.
.