Question

In SN2 reaction, the carbon in the transition state is:

• A. Tri coordinated
• B. Penta coordinated
• C. Tetra coordinated
• D. Hexa coordinated

Hint:

In an SN2 reaction, remember that the transition state forms a five-coordinate structure with the carbon atom, which is tetra coordinated.

Answer 1

The Correct Option is C

In an SN2 reaction, the transition state involves the central carbon atom being bonded to five different entities: the nucleophile, the leaving group, and the two substituents that are attached to the carbon. This results in the carbon being tetra coordinated in the transition state, as it is simultaneously interacting with four groups in a partially bonded manner. Thus, the correct answer is (3) Tetra coordinated.

Answer 2

Step 1: Understanding the SN2 Reaction Mechanism
The SN2 (Substitution Nucleophilic Bimolecular) reaction is a one-step reaction mechanism in which the nucleophile attacks the electrophilic carbon atom from the opposite side of the leaving group. This backside attack leads to the inversion of configuration and the simultaneous breaking and forming of bonds.

Step 2: Nature of the Transition State
In the SN2 transition state, the central carbon atom is in a state where it is partially bonded to both the incoming nucleophile and the leaving group. This occurs as the nucleophile approaches and the leaving group begins to depart. The structure formed at this point is not a stable intermediate, but a transient state of high energy.

Step 3: Coordination Around the Carbon Atom
During this transition state, the central carbon is bonded to three existing substituents and also partially bonded to the incoming nucleophile and the leaving group. As a result, it is effectively connected to four groups. Despite the partial nature of the bonds to the nucleophile and leaving group, the carbon is said to be tetra coordinated in the transition state.

Step 4: Conclusion
Thus, in an SN2 reaction, the transition state features a tetra coordinated carbon atom. This tetra coordination is critical to the reaction mechanism and explains the inversion of configuration observed in SN2 processes.