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Substituent effects on the dehydration of arene hydrates in aqueous solution

O'Mahony, Michelle J.; More O'Ferrall, R.A.; Boyd, D.R.; Lam, C.M.; O'Donoghue, A.C.

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Authors

Michelle J. O'Mahony

R.A. More O'Ferrall

D.R. Boyd

C.M. Lam



Abstract

Rate constants have been determined by UV spectrophotometry at 25 °C for the acid-catalyzed dehydration of different types of monocyclic arene hydrates including those substituted at the 1-, 2- or 3-positions. General acid catalysis was not observed, and linear plots of pseudo-first-order rate constants for dehydration against hydronium concentration were obtained. A Hammett plot of the second-order rate constants for acid-catalyzed dehydration, kH (M−1s−1), of unsubstituted- (8a), 3-substituted (8b, 8c, 8d, 8e) and 1-substituted-benzene hydrates (14f and 14h) shows an excellent correlation with σ+ values and yields a large negative ρ-value of –6.5. The results are consistent with rate-determining formation of a benzenium ion in which direct mesomeric interaction with the substituent occurs, presumably permitted by the coplanar arrangement of the diene and carbocation centre in the intermediate. Data points for 2-substituted arene hydrates (13f, 13g, 13h, 13i) deviate negatively from the Hammett plot as direct mesomeric interaction with the substituent is not possible in the corresponding benzenium intermediates.

Citation

O'Mahony, M. J., More O'Ferrall, R., Boyd, D., Lam, C., & O'Donoghue, A. (2013). Substituent effects on the dehydration of arene hydrates in aqueous solution. Journal of Physical Organic Chemistry, 26(12), 989-996. https://doi.org/10.1002/poc.3174

Journal Article Type Article
Acceptance Date Jun 18, 2013
Publication Date Dec 1, 2013
Deposit Date Oct 11, 2013
Publicly Available Date Mar 29, 2024
Journal Journal of Physical Organic Chemistry
Print ISSN 0894-3230
Electronic ISSN 1099-1395
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 26
Issue 12
Pages 989-996
DOI https://doi.org/10.1002/poc.3174
Keywords Arene hydrates, Dehydration, Substituent effects.

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Copyright Statement
This is the accepted version of the following article: O'Mahony M. J., More O'Ferrall R. A., Boyd D. R., Lam C. M. and O'Donoghue A. C. (2013), Substituent effects on the dehydration of arene hydrates in aqueous solution, Journal of Physical Organic Chemistry, 26(12): 989-996, which has been published in final form at http://dx.doi.org/10.1002/poc.3174. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.





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