SN1 and SN2 reactions (chemistry)

Halogenoalkanes are organic compounds containing a halogen atom connected to an alkyl group. In nucleophilic substitution reactions, these compounds react with a nucleophile (a species with an electron-rich atom, such as a negatively charged ion) to form a new chemical compound.

Primary halogenoalkanes, which contain a single carbon-halogen bond, undergo SN2 substitution reactions. This is because these compounds have a relatively weak carbon-halogen bond. The electron-rich nucleophile is able to attack the carbon atom and form a new bond, resulting in the substitution of the halogen atom.

Tertiary halogenoalkanes, which contain three carbon-halogen bonds, are much more likely to undergo SN1 substitution reactions. This is because the carbon-halogen bonds in these compounds are stronger, making it difficult for the nucleophile to attack the carbon atom. Instead, the carbon-halogen bond breaks, forming a carbocation intermediate. The nucleophile then attacks the carbocation, resulting in the substitution of the halogen atom.

There are some exceptions to these general trends. For example, secondary halogenoalkanes can undergo both SN2 and SN1 reactions depending on the reaction conditions and the type of nucleophile used. Additionally, if the reaction conditions or nucleophile are particularly favorable, a primary halogenoalkane may undergo an SN1 reaction.


Regards Jaydenmaster42

Mostly correct.

You don’t classify halogenoalkanes as 1°, 2° and 3° based on how many carbon-halogen bonds there are: you instead classify them based on how many carbons are bound to the carbon on which the halogen is itself bound.

The effect of the classification of the halogenoalkane on which mechanism the reaction follows is more to do with the steric bulk of the surrounding alkyl groups than it is to do with bond strength.

By any chance, was this a ChatGPT response?

Not really, am also learning, have noted your insight on classification of halogenoalkanes and their reaction

Hello everyone,

I'm having trouble understanding the reactivity of halogenoalkanes in nucleophilic substitution reactions.

Can someone explain why primary halogenoalkanes undergo SN2 reactions, while tertiary halogenoalkanes preferentially undergo SN1 reactions? Also, are there any exceptions to these trends? Thanks in advance.