Acta Crystallographica Section B

Structural Science

Volume 62, Part 6 (December 2006)

research papers

Acta Cryst. (2006). B62, 1112-1120 [ doi:10.1107/S0108768106036421 ]

Interplay between steric and electronic factors in determining the strength of intramolecular N-HO resonance-assisted hydrogen bonds in -enaminones

V. Bertolasi, L. Pretto, V. Ferretti, P. Gilli and G. Gilli

Abstract: The crystal structures of five [beta] -enaminones are reported: (2Z)-3-(benzylamino)-1,3-diphenyl-prop-2-en-1-one, (2Z)-3-(benzylamino)-3-(2-hydroxyphenyl)-1-phenyl-prop-2-en-1-one, (2Z)-3-(benzylamino)-3-(4-methoxyphenyl)-1-(3-nitrophenyl)-prop-2-en-1-one, 2-{1-[(4-methoxyphenyl)amino]ethylidene}cyclohexene-1,3-dione and 2-{1-[(3-methoxyphenyl)amino]ethylidene}cyclohexene-1,3-dione. The structures were analysed and compared with those of similar compounds in order to establish which factors determine the range (2.53-2.72 Å) of NO hydrogen-bond distances in intramolecularly hydrogen-bonded [beta] -enaminones. It has been shown that, beyond electronic resonance-assisted hydrogen-bond effects modulated by substituents, the necessary requirements to produce very short N-HO hydrogen bonding are steric intramolecular repulsions, including the embedding of an enaminonic C-C or C-N bond in an aliphatic six-membered ring. By considering the structural features it is possible to expect the strength of N-HO hydrogen bonds adopted by specific [beta] -enaminones.

Keywords: -enaminones; resonance-assisted hydrogen bonding.


	Structure factor file (CIF format) (225.7 kbytes) [ doi:10.1107/S0108768106036421/bk5040sup2.hkl ] Contains datablock lp6_t150

	Structure factor file (CIF format) (198.8 kbytes) [ doi:10.1107/S0108768106036421/bk5040sup3.hkl ] Contains datablock lp1_150

	Structure factor file (CIF format) (207.9 kbytes) [ doi:10.1107/S0108768106036421/bk5040sup4.hkl ] Contains datablock lp8_150

	Structure factor file (CIF format) (137.6 kbytes) [ doi:10.1107/S0108768106036421/bk5040sup5.hkl ] Contains datablock lp14_150

	Structure factor file (CIF format) (180.1 kbytes) [ doi:10.1107/S0108768106036421/bk5040sup6.hkl ] Contains datablock lp19_150

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