SCHEDULED MAINTENANCE
1H and 13C NMR spectra of some unsymmetric N,N′-dipyridyl ureas: spectral assignments and molecular conformation
Abstract
The 1H NMR spectra of N-(2-pyridyl),
N′-(3-pyridyl)ureas and N-(2-pyridyl),
N′-(4-pyridyl)ureas in CDCl3 and
(CD3)2CO have been assigned with the aid of COSY and
NOE experiments and chemical shift and coupling constant correlations. The
13C NMR spectra in CDCl3 were analysed utilizing the
HETCOR and proton coupled spectra. The 1H NMR spectra, NOE
effects and MINDO/3 calculations have been utilized to show that the
molecular conformation of these compounds has the 2-pyridyl ring coplanar
with the urea plane with the N–H group hydrogen bonded to the
nitrogen of the 2-pyridyl group on the other urea nitrogen while the
3/4-pyridyl group rotates rapidly about the
N–C3/N–C4 bond.
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