Question

Decreasing order of reactivity of alkyl halide is: RCl, RI, RBr.

Answer 1

Part 1: Alkyl halides:

• Alkyl halides are also known as haloalkanes.
• Alkyl halides are the compounds in which hydrogen atoms of an alkyl chain are replaced by halogen atoms.
• The general formula of alkyl halide is $\mathrm{RX}$.
• In this formula, $\mathrm{R}$ is an alkyl group and $\mathrm{X}$ is a halogen atom $(\mathrm{Cl},\mathrm{Br},\mathrm{I},\mathrm{or}\mathrm{F})$

Part 2: Reactivity order of alkyl halides:

• The reactivity of haloalkanes depends upon the size of the halogen atom which is attached to the alkyl group, the length, and the complexity of the alkyl chain.
• Down the group in a periodic table, the atomic size of the elements increases, and electronegativity decreases. Due to this the bond length between carbon and halogen atoms increases from fluorine to iodine. Because among the halogens the size of the fluorine is small whereas iodine is large in size.
• So, the greater the bond length between the atoms greater will be reactivity because it is easy to break the bond..
• Therefore, it is easier to remove iodine atoms than compared to bromine or chlorine atoms, because the size of the iodine is large.

Therefore, the decreasing order of reactivity of alkyl halide is$\mathrm{RI}>\mathrm{RBr}>\mathrm{RCl}$.