The molecular structure of divinylketone studied by gas electron diffraction and ab initio MO calculations

Abstract

The molecular structural parameters of divinyl ketone have been determined by gas electron diffraction and by ab initio MO calculations at the MP2 6-31 Gsu∗ level. The MO calculations predicted the existence of two planar conformers of the molecule: a cis,cis (C,C) and a cis, trans (C,T), the former representing the global energy minimum. The energy difference between C,C and C,T was found to be 1.0 kcal mol −1 both at the SCF and MP2 calculational levels. In the analysis of the electron diffraction data, the theoretically predicted differences between corresponding bond lengths and valence angles in the C,C and C,T conformers were kept fixed. The bond lengths (in terms of r g, Å) and the bond angles (in degrees) as obtained for C,C were as follows: r(CC) = 1.341(4), r(CC) = 1.483(4), r(CO) = 1.219(5), ∠CCC = 121.8(7), ∠CCH = 117.6(25), where numbers in parentheses are uncertainties expressed by 3σ. The relative abundance of the conformers (C,C:C,T), estimated from gas-phase electron diffraction, was 51:49 at 20°C with an uncertainty of about 21%.