
%0 Journal Article
%A Guard, JAM 
%A Steel, PJ 
%T Heterocyclic Tautomerism. VII. X-Ray Structures of Two Crystalline Tautomers of 4-Cinnamoyl-1,3-dimethylpyrazol-5-one
%J Australian Journal of Chemistry
%D 1994/08/01
%V 47
%N 8
%P 1453-1459
%K 
%R https://doi.org/10.1071/CH9941453
%U https://www.publish.csiro.au/paper/CH9941453 
%X The orange crystalline form of 4-cinnamoyl-1,3-dimethylpyrazol-5-one (3) is shown to be the OH tautomer (3e) in which the OH proton is involved in a three-centre hydrogen bond to the intramolecular carbonyl oxygen and to the OH oxygen of an adjacent molecule related by a centre of inversion. Crystals of (3e) are monoclinic, P21/n, a 7.530(3), b 7.960(3), c 20.705(8) &#506;, &#946; 100.16(3)&#176;, Z = 4; the structure was refined to a conventional R(I > 2&#963;(I)) = 0.051. The yellow form of (3) exists as a hydrate in which the NH tautomer (3b) is hydrogen-bonded to the oxygen of a water molecule which in turn is hydrogen-bonded to the carbonyl oxygens of two adjacent molecules. Crystals of (3b) are monoclinic, P21/n, a 8.295(3), b 12.813(4), c 12.888(4) &#506;, &#946; 98.55(3)&#176;, Z = 4; the structure was refined to a conventional R(I > 2&#963;(I)) = 0.054. The structure of (3) in solution is also discussed. 
