And El elimination

I Tertiary7 alkyl halides E2 elimination occurs when a base is used, but SN1 substitution and El elimination occur together under neutral conditions, such as in pure ethanol or water. ElcB elimination takes place if the leaving group is two carbons away from a carbonyl group. 

The substrate is a tertiary alkyl bromide and can undergo SN1 substitution and El elimination under these reaction conditions. Elimination in either of two directions to give regioisomeric alkenes can also occur. 

The Martin sulfurane is an excellent reagent for the rapid dehydration of tertiary alcohols.12 Mechanistically, the dehydration involves ligand exchange around sulfur, diphenylsulfonium ion formation, and El elimination of diphenylsulfoxide to give the alkene (Scheme 8.11). 

Mechanism of the SnI substitution and El elimination reactions of tert-butyl bromide (2-bromo-2-methylpropane). 

Figure 6.4 When a cartoon-hydrogen (or carbon-alkyl) bond is aligned with an empty p orbital, 1,2-hydride/alkyl shifts and El eliminations are favorable.

SjU substitution and El elimination frequently compete in the same reaction. 

The as-decalin is formed because the enone, though flattened, is already folded to some extent. A conformational drawing of either molecule shows that the top surface is better able to bind to the flat surface of the. catalyst. Each of these products shows interesting stereoselective reactions. The ketal can be converted into an alkene by Grignard addition and El elimination and then epoxidized. Everything happens from the outside as expected with the result that the methyl group is forced inside at the epoxidation stage. 

Tertiary alkyl halides E2 elimination occurs when a base such asi OH or RO is used. For example, 2-bromo-2-niiethylpropane gives 97% elimination product when treated with ethoxide ion in ethanol. By contrast, reaction under neutral conditions (heating in pure ethanol) leads to a mixture of products resulting from both S l sub- stitution and El elimination. 

Mostly E2 elimination (Si l substitution and El elimination in nonbasic solvents)... 

In this section, we use concepts developed in our discussion of and S l reactions, and we see how experimental variables affect the product formed in a dehydrohalogenation reaction. The structural features that control and Sj l substitution and E2 and El elimination reactions are related. 

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