What are the chemical properties of Haloalkanes?

What are the chemical properties of Haloalkanes?

Aug 26, 2022, 16:45 IST

CHEMICAL PROPERTIES OF HALOALKANES

The alkyl halides are highly reactive due to high electronegativity difference between carbon and halogen atom, which provides polarity in C δ+ –X δ - bond. Thus, carbon atom of C–X bond is easily attacked by a nucleophile and shows nucleophilic substitution.

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The nucleophilic substitution may follow SN1 or SN2 mechanism. In addition to nucleophilic substitution alkyl halides also show elimination reactions.

SN2 mechanism: The rate of reaction is dependent on the concentration of alkyl halide as well as the nucleophile, i.e.Rate = K[RX][Nu-]. Hence, the reaction is bimolecular nucleophilic substitution. There is complete inversion of configuration as it involves attack of nucleophile from backside.

The order of reactivity of various alkyl halides towards nucleophilic substitution reaction by SN2 mechanism is,

1 ^o > 2 ^o > 3 ^o

SN ₁ mechanism: The rate of reaction is dependent only on the concentration of alkyl halide, i.e. Rate = K [RX]. Hence, the reaction is unimolecular nucleophilic substitution.

The mechanism involves two steps:

Step 1: In the first step, the alkyl halide slowly dissociates into halide ion and carbocation.

Step 2: In the second step, carbocation formed immediately combines with the nucleophile to form the final substituted product.

The order of reactivity of various alkyl halides towards nucleophilic substitution reaction by SN ₁ mechanism is,

3 ^o > 2 ^o > 1 ^o

A racemised product is obtained by SN ₁ mechanism. This is due to the fact that the carbocation formed has planar structure. So, the nucleophile can attack this carbocation from both sides.

What are the chemical properties of Haloalkanes? pdf