| Autor: |
D'Souza MJ; Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA., Sandosky B; Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA., Fernandez-Bueno GA; Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA., McAneny MJ; Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA., Kevill DN; Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA. |
| Jazyk: |
angličtina |
| Zdroj: |
Canadian chemical transactions [Can Chem Trans] 2014 Feb 03; Vol. 2 (2), pp. 160-174. |
| DOI: |
10.13179/canchemtrans.2014.02.02.0093 |
| Abstrakt: |
To provide insight and to identify the occurrence of mechanistic changes in relation to variance in solvent-type, the solvent effects on the rates of solvolysis of three substrates, 2,2,2-trichloro-1,1-dimethylethyl chloroformate, 2,2,2-trichloroethyl chloroformate, and 1-chloroethyl chloroformate, are analyzed using linear free energy relationships (LFERs) such as the extended Grunwald-Winstein equation, and a similarity-based LFER model approach that is based on the solvolysis of phenyl chloroformate. At 25.0 °C, in four common solvents, the α-chloroethyl chloroformate was found to react considerably faster than the two β,β,β-trichloro-substituted analogs. This immense rate enhancement can be directly related to the proximity of the electron-withdrawing α-chlorine atom to the carbonyl carbon reaction center. In the thirteen solvents studied, 1-chloroethyl chloroformate was found to strictly follow a carbonyl addition process, with the addition-step being rate-determining. For the two β,β,β-trichloro-substrates, in aqueous mixtures that are very rich in a fluoroalcohol component, there is compelling evidence for the occurrence of side-by-side addition-elimination and ionization mechanisms, with the ionization pathway being predominant. The presence of the two methyl groups on the α-carbon of 2,2,2-trichloro-1,1-dimethylethyl chloroformate has additive steric and stereoelectronic implications, causing its rate of reaction to be significantly slower than that of 2,2,2-trichloroethyl chloroformate. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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