What type of mechanism do most alcohols undergo when they are converted to alkyl halides using thionyl chloride (SOCl2)?

When alcohols are converted to alkyl halides using thionyl chloride (SOCl2), they typically undergo an SN2 mechanism. This reaction involves a substitution process where the hydroxyl group (-OH) of the alcohol is replaced by a chloride ion (Cl-) from the thionyl chloride.

In this case, the alcohol is protonated first, which makes it a better leaving group, and then the chloride ion attacks the carbon atom attached to the alcohol in a backside attack, displacing the leaving group. This back-to-front approach is characteristic of the SN2 mechanism, where the nucleophile and the leaving group are involved in a single concerted step, leading to the formation of the alkyl chloride.

Moreover, this mechanism is favored for primary and, to some extent, secondary alcohols because steric hindrance is lower, allowing for effective nucleophilic attack. Tertiary alcohols, which are more sterically hindered, do not typically undergo this mechanism effectively and instead would follow different pathways, such as elimination reactions or SN1 mechanisms with a different reagent.

Understanding this adds value to the foundational knowledge of nucleophilic substitution reactions, where the structure of the starting material and the reaction conditions heavily influence the pathway