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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.
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