Halogen Derivatives - Bimolecular Nucleophilic Substitution

Nucleophilic substitution reactions are a group of chemical reactions which are very important in the production of other organic compounds. You are first introduced to this set of reactions through the chemical properties of alkyl halides.

Alkyl halides are reactive because the C-X bond is relatively weak (compared to the C-H bonds in the hydrocarbon chapters) and it is a polar bond. Yes, in the chapter of intramolecular bonding, you learned that the existence of polarity makes the bond stronger.(e.g. the triple bond between C and O in carbon monoxide is stronger than the triple bond between N atoms in nitrogen). This is because there is an added electrostatic attraction between the partial charges.

However, the presence of partial charges, such as a d+ carbon makes the carbon electron deficient. Hence, this makes the carbon susceptible to attacks by a nucleophile - hence alkyl halides are reactive because of its C-X bond. Therefore, alkyl halides undergo nucleophilic substitution.

The following video uses two examples to describe the mechanism of nucleophilic substitution. It is worthwhile to take note that there are two types of nucleophilic substitutions, S_N1 and S_N2. In this articles, I will be focusing on the latter.

If you have further question, you are encouraged to post your questions for discussion.

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^{Article written by Kwok YL 2009.}

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