Sodium 2-naphthoxide is treated with benzyl bromide in four different solvents. In which solvent is the proportion of ring (C-) alkylation, relative to O-alkylation, highest?

The naphthoxide ion is ambident (O or C1). In DMSO, DMF and acetonitrile the oxygen is unsolvated and is the more reactive site, giving mostly the ether. In a strongly hydrogen-bond donating solvent such as trifluoroethanol, the oxygen is tightly solvated and shielded, while the ring carbon is less affected, so C-alkylation becomes much more important.