Question

The correct order of leaving group ability in a nucleophilic substitution reaction is:
 A.\[B{r^ - } > C{l^ - } > C{H_3}CO_2^ - > O{H^ - } > {H^ - }\]
B. \[{H^ - } > O{H^ - } > C{H_3}CO_2^ - > C{l^ - } > B{r^ - }\]
C.\[B{r^ - } > C{H_3}CO_2^ - > C{l^ - } > O{H^ - } > {H^ - }\]
D.\[C{H_3}CO_2^ - > B{r^ - } > C{l^ - } > O{H^ - } > {H^ - }\]

Answer 1

Hint: A nucleophilic substitution reaction involves the displacement of a nucleophile by another species. A nucleophile can be identified as a species which tends to donate electrons and form positive ions.

Complete step by step answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
Electronegativity can be understood as the ability of a chemical species to be able to attract electrons. Higher the electronegativity of the given chemical species, higher is the ability to attract electrons. In the periodic table, there are some trends that are observed. As we move from left to right in a period, the electronegativity of the elements keeps on increasing. Also, as we move down a group, the electronegativity keeps on decreasing.
Now, the electronegativity of a chemical species plays a very important role in defining the leaving group ability of a species. If the electronegativity of a species is high, then its basicity character is low, and hence, the ability of that species to leave also increases. This can be explained by the fact that an increase in the electronegativity results in a species that wants to hold onto its electrons rather than donate them.
The order of electronegativity of the given species can be as given as:
 \[B{r^ - } > C{l^ - } > C{H_3}CO_2^ - > O{H^ - } > {H^ - }\]
Hence, the order of leaving group ability in a nucleophilic substitution reaction can be given as:
 \[B{r^ - } > C{l^ - } > C{H_3}CO_2^ - > O{H^ - } > {H^ - }\]

Hence, Option A is the correct option.

Note:
Alkyl halides undergo many reactions in which a nucleophile displaces the halogen atom bonded to the central carbon of the molecule. Due to which the displaced halogen atom becomes a halide ion.