Answer:
a) SN1/H2O
b) SN1/CH3OH
c)SN2/DMF
d)SN2/HMPA
Explanation:
The reactions are shown in the image attached.
Let me restate the basic facts about SN1 and SN2 reaction mechanisms. SN1 reaction occurs by unimolecular mechanism and involves a carbocation, a poor nucleophile and a polar protic solvent.
An SN2 reaction is a bimolecular synchronous reaction that passes through a single transition state. It requires a good nucleophile and a polar aprotic solvent.
For reaction a and b, we observe that the alkyl halide is tertiary hence the reaction occurs by SN1 mechanism in the presence of a polar protic solvent.
Reactions c and d involves primary and secondary alkyl halides respectively and good nucleophiles. The best solvents to be used are polar aprotic solvents and the reaction follows SN2 mechanism.