How does a reaction change its mechanism? General base catalysis of the addition of alcohols to 1-phenylethyl carbocations

Autor:	William P. Jencks, Rachel Ta-Shma
Rok vydání:	1986
Předmět:	Addition reaction biology Hydrogen bond Chemistry Stereochemistry Alcohol General Chemistry Carbocation Biochemistry Medicinal chemistry Chemical reaction Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Reaction rate constant biology.protein Organic anion
Zdroj:	Journal of the American Chemical Society. 108:8040-8050
ISSN:	1520-5126 0002-7863
DOI:	10.1021/ja00285a027
Popis:	Structure-reactivity correlations are reported for general base catalysis of the addition of alcohols to 1-(4-(dimethylamino)phenyl)ethyl and 1-(4-methoxyphenyl)ethyl carbocations in 50:40:10 H/sub 2/O: CF/sub 3/CH/sub 2/OH:ROH. The addition of trifluoroethanol to the relatively stable ((dimethylamino)phenyl)ethyl cation is catalyzed by substituted acetate ions with ..beta.. = 0.33, which is larger than ..beta.. = 0.23 for addition to the (methoxyphenyl)ethyl cation. Catalysis is more important for the more stable carbocation, but it decreases faster with increasing alcohol basicity. For the water catalysis of alcohol addition to 1-phenylethyl carbocations there is an increased sensitivity to the basicity of ROH with increasing carbocation stability (a Hammond effect). This indicates a small involvement of proton transfer in the transition state and is consistent with simple hydrogen bonding of ROH to a base; it is described by a positive interaction coefficient p/sub yy'/ = delta..beta../sub nuc//-deltasigma. However, for the acetate-catalyzed reaction there is not significant increase in the sensitivity to ROH basicity with increasing carbocation stability.
Databáze:	OpenAIRE
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