Question

Classify the following reaction in one of the reaction types.
\[C{H_3}C{H_2}Br + H{O^ - } \to C{H_2} = C{H_2} + {H_2}O + B{r^ - }\]

Answer 1

Hint:In the given reaction, the saturated compound converted into an unsaturated compound. In this reaction, two main processes are involved one is dehydration and other is dehydrohalogenation.

Complete step by step answer: Given,
The elimination reaction is used to convert a saturated compound containing a single bond into an unsaturated compound containing a double bond.
In elimination reaction, a substrate compound usually alkyl halide by the action of base eliminates hydrogen atom and halogen anion to form alkene.
The elimination reaction takes place in two steps:
(1) Dehydration: Dehydration involves removal of water molecule
(2) Dehydrohalogenation: Dehydrohalogenation of halogen anion.
The elimination reaction is usually two types.
(1) \[{E_1}\] reaction
(2) \[{E_2}\] reaction
The \[{E_1}\] reaction is a unimolecular reaction, it takes place in two steps, first is ionization and second is deprotonation.
The \[{E_2}\]reaction is a bimolecular reaction, it takes place in one step.

The given reaction is shown below.
\[C{H_3}C{H_2}Br + H{O^ - } \to C{H_2} = C{H_2} + {H_2}O + B{r^ - }\]
In this reaction, one mole of ethyl halide reacts with one mole of base (\[O{H^ - }\]) to form one mole of ethene, one mole of water and one bromine ion.
In this reaction, first the lone pair of electrons present in the oxygen of the base will attack the hydrogen from the ethyl bromide and forms a transition state after which the water molecule is removed with bromide ion to form ethene.
Therefore, the reaction is the elimination reaction.

Note:
The given reaction follows the \[{E_2}\] reaction as it has only one step involved which is the formation of the transition state. The reaction rate in this reaction is dependent on the concentration of both the eliminating agent and on the substrate.