Issue 3, 1987

Vibrational spectroscopy and conformations of 2,2-diacylethenamines

Abstract

The i.r., Raman, and 1H n.m.r. spectra of 2,2-diacetylethenamines (3) and 2-aminomethylene-5,5-dimethylcyclohexane-1,3-diones (4) show that these substances exist exclusively in the chelated enamino-diketone form, and that the conjugated system contained in them is essentially planar. The open-chain enamino-diketones (3) exist either in the solid state or in solution in the EZE-conformation (7). A similar conjugated core, having the fixed ZZE-conformation, contained in 5-aminomethylene-2,2-dimethyl-1,3-dioxane-4,6-diones (5) is most probably planar or nearly planar. The EZE- and ZZE- alignments of the enamino-diketones can be distinguished by their spectral properties, and particularly, by their vibrational spectra. Some features of the i.r. and Raman spectra indicate vibrational coupling between the two ν(C[double bond, length half m-dash]O) vibrations, the effect being more marked in the cyclic enamino-diketones (4) and -diesters (5) than in their open-chain analogues. On the other hand, the coupling of the ν(C[double bond, length half m-dash]O) with the ν(C[double bond, length half m-dash]C) and the δ(N–H) modes seems to be less efficient in these enaminodione systems than in the related simple enaninones. Further arguments are presented questioning the criteria established to ascertain the planarity of enamino-diones and of other enamines having two strong electron-acceptor groups at C-2.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1987, 301-306

Vibrational spectroscopy and conformations of 2,2-diacylethenamines

A. Gómez-Sánchez, M. de Gracia García Martín, P. Borrachero and J. Bellanato, J. Chem. Soc., Perkin Trans. 2, 1987, 301 DOI: 10.1039/P29870000301

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