Question

The reactivity of halogen atom is minimum in
(a) Propyl chloride
(b) Propyl iodide
(c) Isopropyl chloride
(d) Isopropyl bromide

Answer 1

Hint: We know that halogens belong to the 17^th group of the periodic table. The halogens are chlorine, iodine, bromine, fluorine, and iodine. The reactivity of halogens is very high and fluorine has the highest electronegativity.

Complete Step by Step Solution:
Let's discuss the reactivity of the halogens. The leaving ability of the halogens decides the reaction rate. And the order of leaving halogens is: Iodine>Bromine>Chlorine>Fluorine. Also, the leaving ability is dependent on the degree of the halogens. The leaving ability order is \[1^\circ > 2^\circ > 3^\circ \].

Here, four alkyl halides are given whose names are propyl iodide, propyl chloride, isopropyl bromide and isopropyl bromide. Let's draw the structures of these alkyl halides.

Fig:Alkyl halides

We know that iodine is the best leaving group. Therefore, propyl iodide is the most reactive among the given alkyl halides.

After iodine, bromine is the good leaving group. Therefore, isopropyl bromide is most reactive from the remaining three alkyl halides.

Now, we have to compare the reactivity of propyl chloride and isopropyl chloride. From the structure, we know that propyl chloride is \[1^\circ \] and isopropyl chloride is \[2^\circ \] carbocation. And we know, reactivity order, that is,\[1^\circ > 2^\circ > 3^\circ \] .
Therefore, isopropyl chloride is the least reactive. Hence, option c is right.

Note: Halogens are the most electronegative elements because they contain seven electrons in the valence shell and thus require only one electron to attain stability. The order of halogens in the electronegativity trend is F > Cl > Br > I.