Consider the following specific laboratory solvents commonly used in organic synthesis: 1. Pure Water 2. Ethanol 3. Dimethyl sulfoxide (DMSO) 4. N,N-Dimethylformamide (DMF) 5. Glacial acetic acid 6. A

Question

Consider the following specific laboratory solvents commonly used in organic synthesis:
1. Pure Water
2. Ethanol
3. Dimethyl sulfoxide (DMSO)
4. N,N-Dimethylformamide (DMF)
5. Glacial acetic acid
6. Acetone
Exactly how many of these solvents strongly and selectively favour the $S_N2$ mechanism over the $S_N1$ mechanism by actively leaving the anionic nucleophile relatively unsolvated and highly reactive?

Prashant Kotian · Accepted Answer

Correct answer: 3. The mechanism is highly favoured by polar aprotic solvents. These solvents effectively dissolve ionic reagents by solvating cations (using their strong negative dipoles), but they lack acidic protons, so they cannot form hydrogen bonds to solvate anions. This leaves the anionic nucleophile "naked" and extremely reactive. Among the options, water, ethanol, and acetic acid are polar protic (they form hydrogen bonds). DMSO, DMF, and acetone are polar aprotic. Thus, exactly 3 solvents strongly favour .

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