Rates of Bimolecular Substitution Reactions in Protic and Dipolar Aprotic Solvents

摘要: Publisher Summary Bimolecular reactions between anions and polar molecules are very much faster in dipolar aprotic solvents than protic solvents. This simple observation has led to a reassessment of the chemistry those rate equilibrium processes that involve solution. Comparison rates S N 2 produce some new conclusions about reaction mechanisms, nucleophilic tendencies, leaving group steric effects, salt solvent affects. chapter discusses several comparisons this type. Protic solvents, such as water, methanol, formamide, acetic acid, ammonia hydrogen-bond donors. Dipolar not donors, but their highly polar. Solvents dielectric constant > ca. 15 only ones generally considered when comparing is an arbitrary choice, made because low constant, ion aggregation so extensive it becomes difficult observe behavior solvent-separated ions. Common are: (1) dimethylformamide (DMF), (2) dimethylacetamide (DMAC), (3) dimethyl sulphoxide (DMSO), (4) hexamethylphosphoramide, (5) tetrahydrothiophen dioxide (sulpholane), (6) sulphone, (7) acetone, (8) nitromethane, (9) acetonitrile, (10) nitrobenzene, (11) sulphur dioxide, (12) propylene carbonate, (13) N-methyl-2-pyrrolidone.