Structure–property relationships in ionic liquids: Influence of branched and cyclic groups on vaporization enthalpies of imidazolium-based ILs

•Ionic liquids [Rmim][NTf2] with iso-alkyl and cyclic substituents were synthesized.•Vaporization enthalpies were measured using quartz-crystal microbalance.•Data consistency was tested by comparison with the homomorph compounds.•Vaporization enthalpies of branched ILs are generally on the same level as for linear.•These findings are useful for the quick estimation of vaporization enthalpies.