Unformatted text preview: /’\ /\ R OH two protons on this [3 carbon R—C—C—CHZR /| i
H CH3 only one proton .
on this B carbon three protons on this [3 carbon Stereoselectivity in Alcohol Dehydration
alkene with less strain preferred
trans disubstituted in chain, cis disubstituted in ring < 11 C
The E1 and E2 Mechanisms of Alcohol Dehydration; Know to write E1 and E2
— 30 and 20 alcohols til mechanism
- 10 alcohols 13; mechanism
The relative reactivity decreases in the order tertiary > secondary > primary
for - Rearrangements in AlcoholDehydration Sometimes the alkene product does not have 1
\ Vii-the same carbon skeleton as the starting alcohol. l l r
\J/ methyl migration or hydride shift 3) dehydrohalogenation of alkyl halides: E2 mechanism for 1°, 2°, 30 halides Base: 3° and 2° NaOCHa, CH30H 1° KOC(CH3)3. (CH3)3COH Regioselective follows Zaitsev's rule more highly substituted double bond
predominates; most substituted alkene(s) preferred Stereoselective more stable conﬁguration of double bond predominates alkene with less strain preferred
trans if unsubstituted chains, cis if unsubstituted rings < 11 C
Know to write the mechanism!
E2: bimolecuiar, one step mechanism. no intermediates
Mechanism of the Dehydrohalogenation of Alkyl Halides: The E2 Mechanism - concerted (one—step) bimolecular process ; single transition state - B-H bond making, C—H bond breaking, 1: component of double bond formation, C—X
bond breaking take place concomitant — Anti Elimination in E2 Reactions: Slereaelectmnic Effects Requires: a) carbon attached to leaving group ...
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- Summer '08
- Organic chemistry