Comparison of Conformations of Diesters of Stabilized Phosphonium Ylides in Solution and in the Crystal
Year: 2008
Type: article
Abstract: Computed bond lengths and angles of methyl ethyl and dimethyl triphenyl phosphonium ylidic diesters, 1b, c , respectively, are similar to those in the crystal, as for the diethyl ester, 1a , where both acyl oxygens are anti to phosphorus. The 1 H and 13 C NMR spectra of the methyl ethyl diester, 1b , where one acyl oxygen is syn and the other anti to phosphorus, are as expected in terms of the conformation in the crystal, but the dimethyl ester, 1c , in the crystal is an equimolar mixture of conformers. For a given ylidic diester the different conformers have similar energies from B3LYP//6-31G(d) computations, interconversions of conformers should not be slow at ambient temperatures and 1 H and 13 C NMR signals in solution are sharp. Estimation of Natural Atomic Charges indicates significant cationoid character on phosphorus and the acyl carbons, and anionoid character on the ylidic carbon and the ester oxygens depending on orientations towards phosphorus.
Institutions: University of Chile, University of California, Santa Barbara
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2019003585