Question

What hybridization best describes the reacting carbon in the \(\mathrm{S}_{\mathrm{N}} 2\) transition state?

Short answer

Answer: The hybridization of the reacting carbon in an SN2 transition state is \(sp^3d\).

Step-by-step solution

Understand SN2 Reaction and Transition State

SN2 reactions are bimolecular nucleophilic substitution reactions, where the nucleophile attacks the carbon atom bonded to a leaving group in a concerted manner and with a well-defined stereochemistry. During an SN2 reaction, the nucleophile attacks from the opposite side of the leaving group, creating a transition state with partial covalent bonds between the nucleophile and the carbon, as well as between the carbon and the leaving group.

Analyze the Geometry of the Transition State

In the SN2 transition state, the nucleophile, reacting carbon, and leaving group lie in a straight line. At this point, carbon will have five electron domains surrounding it— three bonds to other atoms (besides the nucleophile and leaving group) and two partial bonds to the nucleophile and the leaving group. This arrangement of electron domains indicates that the carbon atom will adopt a hybridization that can accommodate five electron domains.

Determine the Hybridization of the Reacting Carbon

Since the reacting carbon has five electron domains, the appropriate hybridization will be one that can accommodate these five domains. The hybridization that can do this is \(sp^3d\).

Conclusion

The best hybridization that describes the reacting carbon in an SN2 transition state is \(sp^3d\).