Conformational identification of cyclohexylphosphine by microwave spectroscopy

The microwave spectra of cyclohexylphosphine have been recorded in the 18.0–26.5 GHz region. A-type rotational transitions have been assigned. The ground state rotational constants were determined to be A = 4153.75 ± 0.23, B = 1362.31 ± 0.01 and C = 1104.14 ± 0.01 MHz for C₆H₁₁PH₂, and A = 4030.03 ± 0.25, B = 1312.72 ± 0.01 and C = 1072.33 ± 0.01 MHz for C₆H₁₁PD₂. From the experimental rotational constants, it is suggested that the assigned spectra have resulted from the chair conformation with the gauche phosphine group in an equatorial position (CESG). This form is believed to be the most populated conformational isomer in the gas phase.