Steric Scale of Common Substituents from Rotational Barriers of N -( o -Substituted aryl)thiazoline-2-thione Atropisomers

Vincent Belot (1) , Daniel Farran (1) , Marion Jean (1) , Muriel Albalat (1) , Nicolas Vanthuyne (1) , Christian Roussel (1)

1 ISM2 - Institut des Sciences Moléculaires de Marseille

A steric scale of 20 recurrent groups was established from comparison of rotational barriers on N-(o-substituted aryl)thiazoline-2-thione atropisomers. The resulting energy of activation ΔG ⧧ rot reflects the spatial requirement of the ortho substituent borne by the aryl moiety, electronic aspects and external parameters (temperature and solvent) generating negligible contributions. Concerning divergent rankings reported in the literature, the great sensitivity of this model allowed us to show unambiguously that a methyl appears bigger than a chlorine and gave the following order in size: CN > OMe > OH. For the very bulky CF 3 and iPr groups, constraints in the ground state decreased the expected ΔG ⧧ rot values resulting in a minimization of their apparent sizes.

Domaines: Chimie

Vincent Belot, Daniel Farran, Marion Jean, Muriel Albalat, Nicolas Vanthuyne, et al.. Steric Scale of Common Substituents from Rotational Barriers of N -( o -Substituted aryl)thiazoline-2-thione Atropisomers. Journal of Organic Chemistry, 2017, 82 (19), pp.10188 - 10200. ⟨10.1021/acs.joc.7b01698⟩. ⟨hal-01682730⟩