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| Content Provider | Royal Society of Chemistry (RSC) |
|---|---|
| Author | Taylor, R. |
| Copyright Year | 1971 |
| Abstract | The rates of pyrolysis of 1-arylethyl acetates containing the 2-CF3, 3-CF3, 4-CF3, 2-NO2, 2-F, 2-Cl, 2-Br, and 2-l substituents have been measured at temperatures between 330·6 and 409·6 °C. A value of +0·565 is obtained for σ+3–CF3 which gives a much better correlation of the data for all electrophilic aromatic substitutions and related reactions, than does the value of 0·52 derived from the solvolysis of t-cumenyl chlorides; use of the latter value should be discontinued. The o-trifluoromethyl substituent is no more deactivating than the meta-substituent and this is attributed to direct stabilisation through space of the electron-deficient reaction centre by the fluorine lone pair. The effect of the o-nitro- and o-halogen-substituents are consistent with the linear correlation of kinetic data for 1-arylethyl acetate and 1-arylethyl methyl carbonate pyrolysis (for which further evidence is given) but the recent use of such correlations to derive σ+(ortho) values is shown to be invalid. A survey of reactions with electron-deficient transition states for which the ortho-halogen substituent effects have been measured shows that where reaction occurs at the α-side chain atom, and where the solvent is either absent or of low polarity, these substituents deactivate more than from the meta-positions; this is rationalised in terms of the direct field effect. The greater deactivation by the o-nitro-substituent relative to the para, parallels that in protodesilylation but not nitration and chlorination which is however not inconsistent with recent theories of substituent effects. |
| Starting Page | 622 |
| Ending Page | 627 |
| Page Count | 6 |
| File Format | |
| ISSN | 00456470 |
| Volume Number | 0 |
| Journal | Journal of the Chemical Society B: Physical Organic |
| DOI | 10.1039/J29710000622 |
| Language | English |
| Publisher | Royal Society of Chemistry |
| Access Restriction | Open |
| Subject Keyword | Pyrolysis Electrophile Solvolysis Substituent Photosynthetic reaction centre Fluorine Lone pair Solvent Nitration |
| Content Type | Text |
| Resource Type | Article |
| Subject | Organic Chemistry Physical and Theoretical Chemistry |
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