CHM 25500 Lecture Notes - Lecture 30: Butene, Nucleophile, Leaving Group

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CHM 255 - Lecture 30 - Beta Elimination Reactions
Beta Elimination Reactions
Beta elimination reactions are those in which a small molecule (such as HCl,
HBr, HI, or HOH) is eliminated from adjacent carbons, resulting in an alkene
Alkyl halide + strong base/ nucleophile -> elimination product + HX
The predominant product of a beta-elimination reaction is the more stable (more
substituted) alkene
In the above reaction, (E)-2-butene and (Z)-2-butene are favored over 1-
butene
There are two main mechanisms for elimination reactions
Beta elimination reactions only occur for species with beta carbons and beta
hydrogens
E1 Reactions
E1 reactions take place in two steps
First the leaving group leaves, resulting in a carbocation intermediate
Then the base/nucleophile attacks the intermediate, plucking a beta hydrogen (a
hydrogen attached to a carbon adjacent to the one bearing the positive charge)
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