N. S. True, R. Bohn
Feb 1, 1977
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0
Influential Citations
20
Citations
Journal
Journal of Molecular Structure
Abstract
Abstract Low resolution microwave spectra of isopropyl formate, fluorofonnate, chloroformate, cyanoformate, and trifluoroacetate each display strong a-type band series associated with a single rotamer. Experimental B+C values for these compounds are: 4641±5; 3172±4; 2275±1/2226±1 MHz ( 35 Cl/ 37 Cl); 2257±1 MHz; and 1509±4 MHz, respectively. In each case the experimental values agree with a τ - 1 (OCOC) = 0°, τ 2 (COCH) ~ 40° structure indicating a modest internal rotation barrier when the methine C—H bond is syn eclipsed with the carboxyl framework. A potential function for the internal rotation of an isopropyl group extrapolated from the known functions in methyl and ethyl formate and one calculated by ab initio methods support the model derived from the low resolution microwave spectra. The single isopropyl conformer observed can be viewed as a combination of the two most stable forms of ethyl esters.