Publication: A computational study of the thermal cis-to-trans isomerization of N-(phenylazo)-substituted N heterocycles

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Title	A computational study of the thermal cis-to-trans isomerization of N-(phenylazo)-substituted N heterocycles
Authors/Editors*	J. Fu, M. Barra
Where published*	Trends in Organic Chemistry
How published*	Journal
Year*	2012
Volume	16
Number
Pages	1-8
Publisher	Research Trends
Keywords	photochromism, triazenes, E/Z isomerization, DFT study, PCM model
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Abstract	The structure and relative stability of ground-state isomeric forms and corresponding transition states for thermal cis-to-trans isomerization of a series of N-(phenylazo)-substituted nitrogen heterocycles were calculated, in cyclohexane and dimethylsulfoxide, using density functional theory combined with the polarizable continuum solvation model. Bond length trends and solvent-induced geometry changes are rationalized in terms of the degree of pi-donation from N-heterocycle to phenylazo moiety. Isomerization is predicted to proceed by a rotation mechanism via a zwitterionic transition state structure. Computed Gibbs energies of activation reproduce trends previously reported; resulting rate constants, however, are ca. 2 to 57 times higher than corresponding experimental values.