title: Substituent effects on the thermal cis-to-trans isomerization of 1,3-diphenyltriazenes in aqueous solution.
abstract: The thermal cis-to-trans isomerization of some symmetrically p,p'-disubstituted 1,3-diphenyltriazenes has been studied by means of laser-flash photolysis techniques. The geometric isomerization is catalyzed by general acids and general bases as a result of acid/base-promoted 1,3-prototropic rearrangements. Acid catalysis becomes more prominent as the electron-donating character of the para substituent increases, while base catalysis becomes more important as the electron-withdrawing character of the para substituent increases. In addition, the rate ascribed to the interconversion of neutral cis rotamers through hindered rotation around the nitrogen-nitrogen single bond is found to decrease as the electron-withdrawing character of the para substituent increases. Rates of interconversion of neutral cis rotamers are also found to decrease with decreasing solvent polarity, which is indicative of the involvement of a polar transition state. On the other hand, kinetic investigations of the acid-catalyzed decomposition of target triazenes are consistent with an A1 mechanism.
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
authors.forename: Nan
authors.initials: N
authors.lastname: Chen
authors.forename: Mónica
authors.initials: M
authors.lastname: Barra
authors.forename: Ivan
authors.initials: I
authors.lastname: Lee
authors.forename: Navjot
authors.initials: N
authors.lastname: Chahal