Which alkyl halide has highest bond enthalpy of $\mathrm{C}-\mathrm{X}$ bond?
Which alkyl halide has highest bond enthalpy of $\mathrm{C}-\mathrm{X}$ bond?
$\mathrm{CH}_3-\mathrm{Cl}$
$\mathrm{CH}_3-\mathrm{F}$
$\mathrm{CH}_3-\mathrm{Br}$
$\mathrm{CH}_3-\mathrm{I}$
Solution
As the size of halogen increases from $F$ to I , $\mathrm{C}-\mathrm{X}$ bond length increases and $\mathrm{C}-\mathrm{X}$ bond strength decreases. With decrease in bond strength, it becomes easier to break the bond by applying minimum energy.
$\mathrm{C}-\mathrm{F}$ bond length is the shortest, so $\mathrm{C}-\mathrm{F}$ bond strength is highest and $\mathrm{CH}_3 \mathrm{~F}$ has the highest bond enthalpy.