Microwave spectra and structural parameters of equatorial-trans cyclobutanol

The microwave spectra of the three singly substituted 13C isotopomers and 18O isotopomer of equatorial-trans cyclobutanol, c-C4H7OH, have been observed in natural abundance by a pulsed-jet Fourier transform microwave spectrometer. The fit for the normal species was improved from the previous study. The rotational constants for the α-13C, β-13C, γ-13C and 18O isotopic species were determined. The five quartic centrifugal distortion constants were determined for the first time. These experimental values are compared to those obtained from ab initio and density functional theory calculations. By utilizing the previously reported microwave rotational constants for the O–D species along with the 15 constants determined from this study combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained. The determined heavy atom distances in Å are: r0(C1–C4,5) = 1.547(3), r0(C6–C4,5) = 1.556(3), r0(C–O) = 1.412(3) Å and angles O 2 C 1 C 4 , 5 = 120.2 ( 5 ) , C 4 C 1 C 5 = 88.9 ( 5 ) and puckering angle τC6C5C4C1 = 31.3(10)°. The parameters are compared to the similar ones for some other monosubstituted cyclobutanes as well as to those for cyclobutane.