An electron diffraction investigation of the molecular structure of formic acetic anhydride

Abstract

The molecular structure of formic acetic anhydride, (HCO)O(CH 3CO), in the gas phase has been determined by the sector-microphotometer method of electron diffraction. The formyl and acetyl fragments are twisted out of the C-O-C plane by 21° and 46°, respectively, giving a dihedral angle between the two moieties of 126°. The bonded interatomic distances, r g(1), are: r(CO) = 1.195, r(C-O) = 1.397 and r(C-C) = 1.495 Å. The valency angles in the acetyl group are: α(O-C-C) = 112° and α(O-CO) = 122°, the formyl valency angles are α(O-CO) = 118° and α(O-C-H) = 120°, and the central C-O-C angle is 113°. The formyl C-H and acetyl CO bonds are nearly parallel, resulting in an H ⋯ O distance of 2.7 Å. The structures of acetic-, formic acetic-, and formic anhydride are compared.