Table 4 13C–1H Coupling constantsa (in Hz) of 1 and 3 in (CD3)2CO
MHz) or Bruker WH (67.89 MHz) FT spectrometers at ambi-
ent temperature. Proton-decoupled and proton-coupled spectra
were recorded. Typical conditions were pulse width 90Њ, spectral
width 200–250 ppm, acquisition time 1 s, and relaxation delay
3–5 s. The number of transients were 5000 to 10 000 to obtain a
good signal to noise ratio. The HETCOSY spectra with hetero-
nuclear decoupling in both dimensions were recorded on 200
MHz instrument. The experimental parameters used were
pulses P1 to P4 correspondingly 98, 196, 9.7 and 19.4 µs, spectral
width 500 Hz, acquisition time 0.5 s, number of transients 32 or
64 and number of experiments 128 or 256.
Carbon
atom
JC,H3/ JC,H4/ JC,H5/ JC,H6/
Compound JC,H2 JC,H3Ј JC,H4Ј JC,H5Ј JC,H6Ј
C2
1
3
1
3
1
3
1
3
1
3
1
3
180.31
177.84
0.00
0.00
11.19
177.84
4.40
0.00
7.10
0.00
2.00
162.73
165.15
3.05
2.00
6.74
6.43
11.25
11.82
9.50
8.50
8.45
8.50
C5
4.20
C6
179.29
11.82
0.00
0.00
6.89
6.80
179.80
179.53
C3Ј
C5Ј
C6Ј
165.66 2.00
164.78 0.00
6.99 0.00
7.00 0.00
0.00 7.39
0.00 7.24
The 1H and proton coupled 13C NMR spectra were simulated
using the computer program 32 LAOCOON-5. Approximate
chemical shifts and coupling constants were obtained from the
experimental spectrum. The theoretical spectrum was generated
by fitting a Lorentzian line-shape to each of the simulated fre-
quencies. It was plotted on a HP plotter using CALCOMP
software. The MO calculations were carried out at the
MINDO/3 level using a standard program.33
166.34
166.45
3.99
3.85
a
As in Table 1.
BBЈCX and AAЈBBЈX (X = 13C) respectively. The C3 and C5
were found to couple to Hα from the simulation of the spec-
trum. The three-bond coupling constants between Hα and C3
and C5 are equal (4.4 Hz). It indicates that for 3, the 4-pyridyl
ring is apparently not coplanar with the urea group and under-
Acknowledgements
1
We gratefully acknowledge the help of the Sophisticated
Instrumentation Centre of the Indian Institute of Science for
recording some of the NMR spectra. Our sincere thanks are
due to Professor S. Manogaran, Indian Institute of Technology,
Kanpur for his valuable suggestions.
goes rapid rotation as inferred from the H NMR spectrum.
The 13C–1H coupling constants of 3 are similar to those of 1
and they are also comparable with those of pyridine and its
derivatives.25–27
Experimental
References
Synthesis
Unsymmetrical N,NЈ-dipyridylureas (RNHCONHR1) are gen-
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(RNH2) under dry conditions.28 Isocyanates are synthesized by
treating an amine with carbonyl chloride (phosgene) which is
highly poisonous and hence advisable to avoid. Isocyanates can
also be obtained by heating acid azides (R1CON3) which could
be obtained by treating the acid chloride (R1COCl) with NaN3.
However, acid chlorides of pyridine-2- and -3-carboxylic acids
are very sensitive to moisture which prevents the formation of
acid azides by this method. Therefore, unsymmetrical N,NЈ-
dipyridylureas were synthesized in the present work by follow-
ing a five-step procedure.
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irradiation time 3–4 s and relaxation delay 5 s. The COSY
experiments were performed using the parameters: pulses P1
and P2 5.7 µs, spectral width 600–800 Hz, preparation time 1–2 s,
number of transients 16 or 32 and the number of experiments
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161