Imidazoline-2-thiones, conformation

Conformational Equilibrium Data for Imidazoline-Thione and Thiobarbituric Acid Derivatives ... 

Although the amount of systematic published material is not great, there have been a number of H NMR studies relating to conformations and configurations of imidazolines and imidazolidines, along with their 0x0 and thione derivatives (B-77SH(i)li3). Most interest has been concentrated on the 2-imidazolines and imidazolinones. In many instances, nearby bulky substituents prefer to take up a trans relationship. Thus when 1,2-diaminoalkanes... 

Other examples are found in A,A -di(RCH2)imidazoline-2-thiones and A,iV -di(RCH2)thiobarbiturates ([36] Berg and Pettersson, 1987), where numerous primary alkyl groups (RCH2) were found to prefer the more crowded syn conformation (Table 5). These conformational preferences, dominated by van der Waals attraction, are nicely reproduced by molecular-mechanics calculations (Carter and Stilbs, 1976 Berg and Pettersson, 1987). 

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