Predict all the alkenes that would be formed by dehydrohalogenation of the following halides with sodium ethoxide in ethanol and identify the major alkene.
(i)    1-Bromo-1-methyl cyclohexane.
(ii)    2-Chloro-2-methyl butane.
(iii)    2, 2, 3-Trimethyl-3-bromopentane.

i) In 1-bromo-1-methylcyclohexane compound, all atoms are equivalent. Thus, dehydrohalogenation of this compound gives only  one alkene.

ii) In 2-chloro- 2-methyl butane compound, there are two different sets of equivalent  atoms. Thus, dehydrohalogenation of the compound yeilds two alkenes.

Saytzeff’s rule implies that in dehydrohalgenation reaction, the alkene having a greater number of alkyl groups attached to a doubly bonded carbon atoms is perferably produced. Hence, alkene (I) is the major product in this reaction.

iii) In the  2, 2, 3-Trimethyl-3 bromopentane compounds, there are two different  atoms. Thus, dehydrohalgenation of the compounds yields two alkenes.


Saytzeff’s rule implies that in dehydrohalgenation reaction, the alkene having a greater number of alkyl groups attached to a doubly bonded carbon atoms is perferably produced. Hence, alkene (I) is the major product in this reaction.