ChemInform Abstract: STRUCTURAL PROPERTIES OF SOME MONOSUBSTITUTED CYCLOBUTANES DETERMINED BY AB INITIO CALCULATION

Abstract

The equilibrium geometries of fluorocyclobutane, C4H7F, chlorocyclobutane, C4H7Cl, cyclobutyl lithium, C4H7Li, cyclobutylium, C4H7+, and the cyclobutyl negative ion, C4H7−, have been computed ab initio by Hartree—Fock gradient calculations with basis sets which are double zeta in the valence shells and augmented with d functions on F, Cl, and Li. Two stable conformers with the substituent (or lone pair) in the equatorial and in the axial positions were found in each case, except for C4H7+ where the only stable conformation had the hydrogen atom at the carbonium carbon 4.8° out of planarity. For the other materials, the relative stabilities of the two conformers varied with the electron-donating or electron-withdrawing character of the substituent, with Eeq—Eax being 11.9 kJ mol−1 for C4H7−, 1.8 for C4H7Li, —4.3 for C4H7Cl, and —9.1 for C4H7F. The ring-puckering angle for the equatorial forms varied only slightly in the direction F & Cl & Li & — while it showed a considerably greater variation in the reverse direction for the axial conformers. The ring CC bonds adjacent to the substituent were shortened slightly for electron-withdrawing substituents and lengthened for electron-donating ones.