MOLECULAR-STRUCTURE AND CONFORMATION OF METHYL ACRYLATE - A GAS ELECTRON-DIFFRACTION STUDY AUGMENTED BY AB-INITIO CALCULATION AND ROTATIONAL-CONSTANTS

The molecular structure and conformational properties of methyl acryla te, CH2=CH-CO-O-CH3, were studied by a joint analysis of gas electron diffraction data and rotational constants. The structures optimized by HF/4-31G ab initio calculations taken from the literature were utili zed as structural constraints in the data analysis. Mean amplitudes of vibration and shrinkage corrections were calculated on the basis of t he vibrational spectra recorded for this analysis. At room temperature the molecule exists in a conformational equilibrium of two forms, s-c is and s-trans, in a ratio of 67(11):33. The following r(z) structural parameters were found for the s-cis conformer: r(C=C) = 1.332(7) Angs trom; r(C-C) = 1.480(6) Angstrom; r(C=O) = 1.207(2) Angstrom; r(C(=O)- O) = 1.345(3) Angstrom; r(O-C-Me) - r(C(=O)-O) = 0.089 Angstrom (assum ed); r(C-H) = 1.079(5) Angstrom (averaged value); angle C=C-C = 120.3( 8)degrees; angle C-C=O = 126.1(5)degrees; LC-C-O = 110.3(3)degrees; an gle C-O-C = 116.4(5)degrees. Parenthesized values are error estimates (3 sigma) referring to the last significant digit.