Microwave, infrared, and Raman spectra, r0 structural parameters, conformational stability, and vibrational assignment of allyl thiol

Abstract

FT-microwave spectrum of allyl thiol, H 2C CHCH 2SH, has been recorded, and 19 transitions have been assigned for the most abundant isotopologue of Gg conformer, and the rotational constants have been determined; A = 20,041.439 (4), B = 2795.830 (1), C = 2701.084 (1). From the determined microwave rotational constants and ab initio MP2(full)/6-311 + G(d,p) predicted structural values, adjusted r 0 parameters are reported with distances (Å): rC C = 1.343 (3), rC–C = 1.496 (3), rC–S = 1.827 (3) and angles (°) ∠CCC = 123.4 (5), ∠CCS = 112.5 (5), and τC γC βC αS = 118.7 (5). Variable temperature (−55 to −100 °C) infrared spectra (3600–400 cm −1) were recorded of allyl thiol in liquid xenon and the Gg conformer was determined to be the most stable form. The enthalpy differences relative to the Gg form are for Cg 120 ± 9 cm −1 (1.44 ± 0.11 kJ/mol), for Gg′ 337 ± 34 cm −1 (4.03 ± 0.41 kJ/mol), and for Gt 360 ± 36 cm −1 (4.31 ± 0.43 kJ/mol). The relative amounts present at ambient temperature are Gg 52 ± 1%, Cg 29 ± 1%, Gg′ 10 ± 1%, and Gt 9 ± 1%. The conformational stabilities have been predicted from ab initio calculations with many basis sets up to aug-cc-pVTZ and the predicted stabilities are in agreement with the experimentally determined order. Vibrational assignments are reported with support by ab initio predictions and results are discussed.