Steric Enhancement of Resonance - Evidence from Kinetic Study on some Acetophenones
| Main Authors: | M. KRIHNA PILLAY, S. PALANIVELU |
|---|---|
| Format: | Article Journal |
| Bahasa: | eng |
| Terbitan: |
, 1986
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/6277471 |
Daftar Isi:
- Department of Chemistry, Bharathidasan University, Tiruchirapalli-690 028 Manuscript received 16 December 1986, revised 10 July 1986, accepted S September 1986 The kinetics of oxidation of some mono-, di- and tri-substituted acetophenones by alkaline hexacyanoferrate(III) in 50% (v/v) methanol—water mixture at constant ionic strength and at 20, 30 and 40° have been studied spectrophotometrically and the rate constants determined by least-squares analysis. Electron-withdrawing groups in the ring facilitate the oxidation of the acetyl function while electron-releasing groups retard the rate The rate constant values for the oxidation of 3-substituted-4 alkoxyacetophenones are computed based on the principle of additivity of group effects. The observed rate constants are significantly lower than the calculated values. This is attributed to the phenomenon of steric enhancement of resonance (SER). 3,5-Disubstituted-4-methoxyacetophenones have higher observed rate constant values than the calculated ones. The steric inhibition of resonance (SIR) operates in these systems. In the case of 3-halogens-4-methoxyacetophenones, the importance of SER increases with increase in the bulkiness of the 3-substituents. The difference between the calculated and observed multiple substituent constants of 3-substituted-4-methoxyacetophenonas also lends support for SER.