10-22-08 - 318M Krische, Lecture 24: W - 10/24/03, Ch. 8,

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318M – Krische, Lecture 24: W - 10/24/03, Ch. 8, Substitution/Elimination We discussed how S N 1 and E1 are competitive pathways. The factors which favor S N 1 include a poor nucleophilie, a 3 o halide, and a protic solvent. Factors which favor E1 include a basic nucleophile, a 3 o halide, and a protic solvent. We also saw that the E1 mechanism can be favored over S N 1 if a bulky nucleophile (e.g. the tert -butoxide anion) is used. Here, the steric bulk of the nucleophile prevents approach to the tertiary center, making deprotonation of the neighboring hydrogen relatively faster. You should be able to draw energy vs. reaction progress diagrams for both the S N 1 and E1 processes . We saw that the E1 reaction is a regioselective process. The major product tends to be the most highly substituted alkene possible. By considering heats of hydrogenation, we saw that more highly substituted alkenes are more stable (Zaitsev’s rule). We also considered the regioselectivity in the context of an energy vs. reaction progress diagram.
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This note was uploaded on 02/09/2009 for the course CH 318M taught by Professor Bocknack during the Fall '08 term at University of Texas at Austin.

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