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

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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(Cα–Cβ) = 1.525±0.005 Å r(Cβ–Cγ) = 1.550±0.005 Å, r(Cα–Cl) = 1.775±0.005 Å, ∠Cl–(CβCαCβ) = 135°±1°, and ∠(CβCαCβ)– (CβCγCβ) = 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 χaa = −56.58±0.10 Mc/sec and χcc = 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–(CβCαCβ) = 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: μa = 1.870±0.005 D, μc = 0.52±0.02 D, and μ = 1.94±0.01 D.