Notable Substituent Effects on the Rate Constant of Thermal Denitrogenation of Cyclic Azoalkanes: Strong Evidence for a Stepwise Denitrogenation Mechanism
Chizuko Ishihara A and Manabu Abe A B CA Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
B Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
C Corresponding author. Email: mabe@hiroshima-u.ac.jp
Australian Journal of Chemistry 63(12) 1615-1618 https://doi.org/10.1071/CH10281
Submitted: 26 July 2010 Accepted: 12 August 2010 Published: 6 December 2010
Abstract
The thermal denitrogenation rates (k) of a series of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives 2 with a variety of aryl groups (p-CNC6H4, C6H5, p-MeC6H4, p-MeOC6H4) were determined to investigate the denitrogenation mechanism. A linear correlation (r = 0.988) between the relative rate-constant (log krel) of the denitrogenation reaction and Arnold’s σα• parameter for benzylic-type radical-stabilization was observed. However, the relative rate-constant was not correlated with the substituent effect on the lifetime of the resulting singlet diradicals DR2. These results indicate that the rate-determining step of denitrogenation of 7,7-dimethoxy-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives involves stepwise C–N bond cleavage.
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