title: The vaporization enthalpies of 2- and 4-(N,N-dimethylamino)pyridine, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, imidazo[1,2-a]pyridine and 1,2,4-triazolo[1,5-a]pyrimidine by correlation-gas chromatography.
abstract: The vaporization enthalpies of a series of heterocyclic compounds some suspected of showing evidence of a higher degree of self-association in comparison to many other nitrogen heterocycles have been measured both by correlation gas chromatography (CGC) and for comparison by transpiration. The compounds share some structural similarities. They include 2- and 4-(N,N-dimethylamino)pyridine, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,2,4-triazolo[1,5-a]pyrimidine and imidazo[1,2-a]pyridine. The vaporization enthalpies of the first three of the compounds are well reproduced by a standard series of reference compounds, mainly pyridine derivatives. The latter two compounds and 4-(N,N-dimethylamino)pyridine exhibit vaporization enthalpies approximately 7 kJ·mol(-1) larger. Their values are reproduced by using standards previously shown to exhibit stronger but similar self-association properties. The crystal structure of 1,2,4-triazolo[1,5-a]pyrimidine has been determined in an effort to understand the nature of the self-association. The molecule crystallizes in planar stacks slightly offset with a stacking distance of 3.24 Å.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Nano Science, University of Missouri-St. Louis, St. Louis, Missouri 63121, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Lipkind
authors.forename: Nigam
authors.initials: N
authors.lastname: Rath
authors.forename: James S
authors.initials: JS
authors.lastname: Chickos
authors.forename: Vasiliy A
authors.initials: VA
authors.lastname: Pozdeev
authors.forename: Sergey P
authors.initials: SP
authors.lastname: Verevkin