X-ray and nmr spectroscopic study of substituted 2-alkylidene-7-diethylaminobenzopyrans
The structures of 4-methyl-7-diethylamino-2-(acetylcarbethoxymethylene)- and 4-methyl-7-diethylamino-2-(cyanocarbethoxymethylene) benzopyran were investigated by X-ray structural analysis. It was shown that the crystalline compounds have strong intramolecular charge separation and a single conformation in which the largely acceptor substituent, exomethylene, is near atom 3-H of the benzopyran fragment. Based on low temperature NMR spectra, it was concluded that an analogous conformation predominates in solution.