The mechanism of oxymercuration involves a series of steps that begin with electrophilic addition, where a double bond in an alkene reacts with an electrophile, in this case, a mercury species (HgOAc₂). The acetyl groups (OAc) attached to mercury create a strong partial positive charge on the mercury, making it a suitable electrophile. The double bond attacks the mercury, resulting in the formation of a bridged ion known as a mercurium ion. This ion is characterized by a positive charge distributed across the three atoms involved, leading to a unique structure that differs from typical carbocation formation seen in hydration reactions.

In the next step, water acts as a nucleophile, attacking the mercurium ion. The site of attack is determined by the stability of the resulting carbocation; the more substituted carbon (tertiary) is favored due to its ability to stabilize the positive charge better than a secondary carbon. This attack follows an SN2 mechanism, where the nucleophile approaches from the opposite side of the leaving group, leading to a stereochemical outcome where the groups end up in opposite orientations.

Upon the nucleophilic attack by water, the strained three-membered ring opens, resulting in the mercury being pushed to the opposite side of the attack. This leads to the formation of an alcohol at the more substituted carbon, while the original methyl group is positioned at the back. The final step involves demercuration, where a reducing agent, such as sodium borohydride (NaBH₄), replaces the mercury with a hydrogen atom, yielding the final product: an alcohol that adheres to Markovnikov's rule, with the hydroxyl group positioned at the more substituted carbon and the groups arranged in an anti configuration due to the mechanism's nature.

This reaction is significant in organic chemistry, as it provides a reliable method for converting alkenes into alcohols while following specific regioselectivity and stereochemistry principles. Understanding this mechanism is crucial for mastering organic synthesis and preparing for examinations.

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