Microwave Spectra, Dipole Moments, Structure, and Ring Puckering Vibration of Cyclobutyl Chloride and Cyclobutyl Fluoride

Abstract

Microwave spectra of nine isotopic species of cyclobutyl chloride and of the normal species of cyclobutyl fluoride have been studied. From the ground state moments of inertia, the structure of cyclobutyl chloride has been determined. Some of the more important structural parameters are: r(C_α–C_β) = 1.525±0.005 Å r(C_β–C_γ) = 1.550±0.005 Å, r(C_α–Cl) = 1.775±0.005 Å, ∠Cl–(C_βC_αC_β) = 135°±1°, and ∠(C_βC_αC_β)– (C_βC_γC_β) = 20°±1°. The chlorine atom is found at the equatorial position of the puckered ring, and the axial form was not observed. Quadrupole coupling constants of the chlorine atom for CH₂CH₂CH₂CH³⁵Cl species were found to be χ_aa = −56.58±0.10 Mc/sec and χ_cc = 23.60±0.1 Mc/sec. The transformed coupling constant along the C–Cl bond is −65.98 Mc/sec (assuming the quadrupole tensor was axially symmetric about the C–Cl bond). The moments of inertia of cyclobutyl fluoride calculated using r(C–F) = 1.37 Å, ∠F–(C_βC_αC_β) = 132° and the remaining structural parameters of cyclobutyl chloride agreed with the observed moments of inertia. The dipole moments of cyclobutyl fluoride were determined by the Stark effect: μ_a = 1.870±0.005 D, μ_c = 0.52±0.02 D, and μ = 1.94±0.01 D.