Hindered internal rotation in 3,4-di-isopropyl-Δ4-thiazoline-2-thione from temperature-dependent nuclear magnetic resonance spectra of five different groups of protons: a methodological study

Abstract

The internal rotation of the isopropyl groups in 3,4-di-isopropyl-Δ⁴-thiazoline-2-thione has been studied by complete n.m.r. bandshape analysis of the five possible groups of protons in the molecule. The agreement among the derived sets of thermodynamic activation parameters is quite satisfactory, leading to the following average values: ΔG^‡_{298.2 K} 65.4 kJ mol^–1(15.64 kcal mol^–1), ΔH^‡ 59.8 ± 0.6 kJ mol^–1(14.3 ± 0.1 kcal mol^–1), and ΔS^‡–18 ± 2 J mol^–1 K^–1(–4.4 ± 0.4 cal mol^–1 K^–1). The effect of different methods of evaluation of the relaxation parameter, T₂, on the resulting activation parameters and the relevance of the small negative entropy value for the interpretation of the nature of the rotational process are discussed.