Question

One of the following that cannot undergo dehydro-halogenation is:
A. Iso-propyl bromide
B. Ethanol
C. Ethyl bromide
D. None of these

Answer 1

Hint: A reaction in which the removal of a hydrogen halide group takes place from an organic compound is termed a dehydro-halogenation reaction. This reaction happens because of the reaction of an alkyl halide and potassium hydroxide whose nature is alcoholic.

Complete Step by Step Solution:
Here, we have to find the compound that cannot undergo a dehydro-halogenation reaction. The dehydrohalogenation reaction happens only when the organic compound is an alkyl halide.

The organic compound that is, isopropyl bromide contains a halogen group. Therefore, it undergoes a dehydro-halogenation reaction. So, option A is wrong.

Option C is ethyl bromide. It is an alkyl halide. Therefore, it undergoes a dehydro-halogenation reaction. So, option C is wrong.

Option B is ethanol. Its chemical formula is \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH}}\] . So, no halogen group is present in the compound. Therefore, it does not give a dehydro-halogenation reaction.
Therefore, option B is right.

Additional Information: In organic chemistry, the preparation of alkene from alkyl halide happens by the process of dehydro-halogenation. In dehydrohalogenation, the removal of HX happens from the adjacent atoms. This reaction happens in the presence of heat and a base. For example, the conversion of n-butyl chloride to but-1-ene takes place through a dehydrohalogenation reaction:
\[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{Cl}} \overset{Alc KOH, Heat}{\rightarrow} {\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{CH = C}}{{\rm{H}}_{\rm{2}}}\]

Note: It is to be noted that the dehydrohalogenation reaction is termed an elimination reaction because of the elimination of HX (X=Halogen) from the compound. And the alcoholic KOH is used for the dehydrohalogenation reaction. The aqueous KOH, when used, gives a substitution reaction.