ISSN:
1572-8854
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract N,N′-diphenyl-N-(2-pyridinyl)urea hemihydrate (C18H15N3O·1/2H2O) has been studied by crystallographic and NMR-spectroscopic methods. The crystals are monoclinic,I2/a with unit-cell parameters at 86K,a=17.820(1),b=14.857(1),c=11.299(1) Å,β=99.17(1)° andZ=8. The structure was solved by direct methods which involved the use of seventeenmeasured triplet phases in the starting set. This appears to be the first centrosymmetric structure solution being based extensively on physically acquired X-ray phases. Refinement was by full-matrix least-squares involving 3843F o and yieldedR∼R w=0.042. The shape of the molecules can be described approximately by two, nearly orthogonal planes, one containing pyridine, the urea group and the NH-bonded phenyl ring, the other containing the second phenyl ring. Both the X-ray and the NMR studies show that there is an intramolecular H-bond between the urea N and the pyridine N atoms. When pH is lowered, this H-bond is weakened, and eventually breaks due to protonation of the pyridine ring. The X-ray study indicates that about 20% of the pyridine rings in the crystal are protonated. The structure details of the rings, in particular the valency angles, have been analyzed in relation to the orientation of the rings relative to the main molecular plane, and the electronic effects of the substituants.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01164294
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