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Effect of solvent on cis ‐to‐ trans isomerization of 4‐hydroxyazobenzene aggregated through intermolecular hydrogen bonds
Author(s) -
Kojima Masanobu,
Nebashi Satomi,
Ogawa Keiichiro,
Kurita Noriyuki
Publication year - 2005
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.944
Subject(s) - chemistry , isomerization , cyclohexane , intermolecular force , solvent , triethylamine , benzene , solvent effects , hydrogen bond , cis–trans isomerism , photochemistry , acetonitrile , ab initio , computational chemistry , medicinal chemistry , organic chemistry , catalysis , molecule
The half‐life (τ 1/2 ) for thermal isomerization of cis ‐4‐hydroxyazobenzene ( c ‐HOAB) to its trans isomer is highly dependent on the solvent used. For non‐aromatic solvents, the cis isomer is extremely unstable at 293 K (τ 1/2 < 1 min in methanol and acetonitrile and 6 min in cyclohexane), whereas the cis isomer is surprisingly stable in benzene (τ 1/2 = 125 min). However, addition of hydrogen chloride and triethylamine in benzene causes a remarkable decrease in τ 1/2 . On the basis of ab initio molecular orbital calculations of the binding energies and the optimum structures of c ‐HOAB–solvent complexes, a mechanism for the thermal cis ‐to‐ trans isomerization reaction involving hydrogen‐bonded dimers and complexes is suggested. Copyright © 2005 John Wiley & Sons, Ltd.