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The Curtius rearrangement of some organic azides: A DFT mechanistic study
Author(s) -
Kakkar Rita,
Zaidi Sheza,
Grover Rajni
Publication year - 2008
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.21911
Subject(s) - curtius rearrangement , chemistry , isocyanic acid , isomerization , azide , transition state , concerted reaction , reaction mechanism , nitrene , photochemistry , moiety , computational chemistry , singlet state , medicinal chemistry , stereochemistry , catalysis , organic chemistry , excited state , physics , nuclear physics
The reaction mechanism for the thermal Curtius reaction of formyl azide has been investigated using B3LYP/6‐311+G(d,p). It is found that, while the synisomer undergoes nitrogen elimination via a concerted mechanism, yielding isocyanic acid directly, the anti‐isomer cannot undergo reaction via the concerted mechanism and first eliminates nitrogen, yielding oxazirene, via a transition state which is higher in energy than that for the concerted mechanism. Singlet formyl nitrene does not exist as an independent moiety. Rather, the strong NO interaction yields the cyclic isomer oxazirene. The isomerization of oxazirene to isocyanic acid goes through a transition state which is even higher in energy than that for nitrogen elimination. It is hence proposed that this reaction should take place via the concerted mechanism only, the anti‐isomer undergoing isomerization first to the syn isomer since the activation barrier for this step is very small. The same mechanism is found to prevail for acetyl and benzoyl azide. These findings are in accord with all experimental data. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009