Relationships among strain energies of mono-and poly-cyclic cyclohexanoid molecules and strain of their component rings

The standard molar enthalpies of vaporization Delta(1)(g)H(m)(o) of N-(hydroxyethyl)-piperazine, I m bis-piperidino-methane, 1,3,5-tri-methyl-hexahydro-s-triazine, and also the enthalpies of sublimation Delta(cr)(g)H(m)(o) of N,N'-di(hydroxyethyl)-piperazine, and hexamethylenetetramine were obtained from the temperature dependence of the vapor pressure measured in a flow system. The standard molar enthalpies of formation Delta(f)H(m)(o)(1) at the temperature T = 298.15 K were measured by means combustion calorimetry for bis-piperidino-methane and 1,3,5-tri-methyl-hexahydro-s-triazine. Strain enthalpies (ring-correction terms) of these cyclohexanoid molecules were derived from the experimental enthalpies of formation of the gaseous Compounds. These experimental results, together with data available from the literature, provided a quantitative understanding of the interrelations of structure and energetics of a mono- and poly-cyclic cyclohexanoid molecules and strain of their component rings. (C) 2002 Elsevier Science Ltd. All rights reserved.