All comparisons assume the same temperature and comparable reagent thermodynamic activities in methanol.
- Iodomethane: faster, because iodide is a better leaving group and the C-I bond is more readily broken than C-Cl.
- 1-Chloropropane: slower than methyl chloride for SN2, because its ethyl substituent crowds backside approach and raises the substitution barrier. It is still a primary substrate, so SN2 remains plausible.
- MeSNa: generally faster substitution with methanethiolate than methoxide in this protic solvent. Sulfur is more polarizable and its larger anion is less strongly hydrogen-bond-solvated, making it a better nucleophile here. This must not be inferred simply from basicity: methanethiolate is the weaker base.
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