Question

In dehydrohalogenation reaction, hydrogen and halogen are removed from:
A.The same carbon atom
B.The adjacent carbon atoms
C.The isolated carbon atoms
D.Any two carbon atoms

Answer 1

To answer this question, recall the concept of dehydrohalogenation reaction. Dehydrohalogenation reaction is a type of elimination reaction. In an elimination reaction, an alkyl halide eliminates one equivalent of acid to form an alkene.

Complete step by step answer:
As dehydrohalogenation is an elimination reaction, here, elimination of hydrogen atom and a halogen atom from adjacent atoms in a molecule takes place resulting in the formation of an alkene or an alkyne with the release of hydrogen halide. The equation showing the dehydrohalogenation reaction is:
$R - C{H_2} - CH(X) - R \to R - CH = CH - R + HX$
From the above equation, it is evident that in the process of dehydrohalogenation hydrogen and halogen are removed from adjacent carbon atoms. The reaction is also known as $\beta$ dehydrohalogenation because the hydrogen atom removed is from the $\beta$ carbon, i.e. the adjacent carbon.

Hence, the correct option is B.

Note:
In case of elimination reaction when more than one elimination product is possible Saytzeff’s Rule comes into the picture. This Saytzeff’s Rule is also known as Zaitsev’s rule, Saytzev’s rule or Z-rule. Alexander Zaitsev performed the analysis of different elimination reactions with their mechanisms and observed a general pattern in the resulting alkenes. He stated that stable alkene is formed when the removal of hydrogen from $\beta$ carbon has a low number of hydrogen substituents. According to this rule, the most substituted alkene is the most stable product. This law does not explain stereochemistry and just generalizes the regiochemistry of the elimination reaction.