Question

Dehydrohalogenation in mono haloalkanes produces
A. A single bond
B. A double bond
C. A triple bond
D. Fragmentation

Answer 1

Hint: By the word mono in mono haloalkanes means that only one halogen group is attached to an alkyl compound. Dehydrogenation is a reaction where a hydrogen atom is removed whereas dehalogenation is the removal of the halogen group. Therefore, the reaction dehydrohalogenation means the removal of hydrogen and halogen atoms.

Complete Step by Step Solution:
Dehydrohalogenation: Dehydrohalogenation is the method usually used for the preparation of alkenes from alkyl halides. In this reaction, the HX group is removed where H is the hydrogen atom and X is the halogen atom. This reaction takes place by heating in the presence of ethanol and potassium hydroxide where ethanol is used as a solvent.

Alkene is the hydrocarbon containing a carbon-carbon double bond.
Mono Haloalkanes are the compound where only the halogen group is attached to the alkyl group. An example of mono haloalkane is n-butyl chloride.
The reaction of dehydrohalogenation of n-butyl chloride is shown below.
\[C{H_3}C{H_2}C{H_2}C{H_2}Cl
\xrightarrow[Heat]{KOH(alc)} C{H_3}C{H_2}CH = C{H_2} + HCl\]
In the above reaction n-butyl chloride is heated with alcoholic potassium hydroxide to form but-1-ene as the main product by eliminating hydrochloric acid.
Thus, dehydrohalogenation in mono haloalkanes produces a double bond.
Therefore, the correct option is B.

Note: It should be noted that if more than one alkene compound is formed in the reaction, than the more substituted alkene is considered the major product. In the reaction, the hydrogen is removed from the beta carbon that is the adjacent carbon to the carbon to which halogen is attached.