Spectra and structure of organophosphorus compounds. XXXIV. The r s and r structures of t r a n s and g a u c h e ethylphosphine

Abstract

The microwave spectra of 11 chemically different isotopic species of ethylphosphine (CH3CH2PH2) including all 13C and D single substituted species were recorded and assigned for the vibrational ground state. The b- and c-type transitions of the gauche conformers with symmetrically substituted ethyl groups and a PH2 group were found to be split due to tunneling between the equivalent forms. The spectra of these molecules were fit to a Hamiltonian containing Coriolis interaction terms. All other spectra were fit to asymmetric rotors with quartic centrifugal distortion. Complete rs structures were obtained for both the trans and gauche conformations. The r0 structures were derived from 45 and 48 rotational constants for the trans and gauche forms, respectively. Significant differences in the structures were found with the most notable one in the CCP angle which changes from 110.5° in the gauche form to 116° in the trans conformer. The methyl group in the gauche conformation is rotated away from a position symmetric with respect to the heavy atom plane. The structural differences are attributed to nonbonded repulsive interactions between the methyl and phosphino hydrogen atoms.