Structure of the azetidine radical cation and the neutral azetidin-1-yl radical. An ab initio and electron paramagnetic resonance study

Abstract

The electronic structures of the azetidine radical cation and the neutral azetidin-1-yl radical have been investigated by EPR spectroscopy and theoretical ab initio UHF, MP2 and SDCl calculations. The radical cation was assigned a structure with a planar ring according to the theoretical and experimental results. Ab initio UHF calculations predicted the neutral azetidin-1-yl radical to have a puckered ring structure, with puckering angles 12.0 and 15.4° on the STO-3G and 6-31G* levels, respectively. This result was supported by the observed nonequivalent values of the experimental β-proton hyperfine coupling constants, suggesting that the neutral radical has a puckered structure at low temperature in a solid halocarbon matrix. Calculated SDCl values for the isotropic and anisotropic hyperfine coupling constants of the azetidine cation and the azetidin-1-yl radical were found to be in qualitative agreement with the experimental data.