Microwave spectrum and rotational isomerism in isopropyl mercaptan

• Published in: Journal of molecular spectroscopy 1975-01, Vol.56 (2), p.257-269
• Main Authors: Griffiths, John H., Boggs, James E.
• Format: Article
• Language: English
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/0022-2852(75)90240-4

A microwave investigation of isopropyl mercaptan has established the existence of both trans and gauche conformers, the trans being more stable by 57 cal mole −1. Stark effect measurements give the dipole moments as 1.61 ± 0.2 D for the trans and 1.53 ± 0.2 D for the gauche species. The spectra of the isotopic species (CH 3) 2CH 32SD, (CH 3) 2CH 34SH, and (CH 3) 2CH 34SD of the trans form have also been analyzed, providing a limited amount of structural data. The rotational spectrum of the gauche isomer is noticeably influenced by inversion. Interactions between energy levels in the two lowest inversion states have been satisfactorily accounted for in terms of rotational constants, coupling parameters ( G a and G c ), and Δ E 0, the inversion level splitting. Δ E 0 is found to be 562.4 MHz for the ground state of (CH 3) 2CHSH and 10.0 MHz for (CH 3) 2CHSD. A value of 1.98 kcal mole −1 has been calculated for the barrier to internal rotation of the -SH group in terms of a V 3 potential.