GRE Subject Test: Chemistry : Substitution Reactions
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
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Example Questions
Example Question #3 : Substitution Mechanisms
In reactions involving the alkylation of acetylide ions, it is preferred that the alkyl halide be primary. What is the reason for this?
The reactions generally occur in two steps
The mechanism for these reactions is SN2
The mechanism for these reactions is SN1
An answer cannot be determined without more information about the reaction conditions
The reaction involves a carbocation as intermediate
The mechanism for these reactions is SN2
The reason that the alkyl halide is preferred to be primary is because the mechanism for these reactions is SN2. SN2 indicates a substitution reaction that takes place in one step. A primary alcohol is preferred to prevent steric congestion caused by the simultaneous binding of the nucleophile and release of the leaving group. This reaction mechanism is faster because it omits the formation of a carbocation intermediate.
In contrast, SN1 reactions take place in two steps and involve the formation of a carbocation intermediate.
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