
Josh G. answered 03/25/19
PhD in Chemistry, specializing in organic chemistry
Outside of the rules you may learn for Sn1, Sn2, E1, E2 the choice of solvent isn't clear. First the solvent should attempt to dissolve all your components. Often times reactions cannot occur if they are out of solution, but there are some cases where they can. Second you want to make sure that your solvent does not have adverse reactivity with any of your components. This may consume some of your reagents and get undesired products. This is why for a Grignard you would more likely use an ether over an alcohol. Third, often times chemists randomly try a bunch of different solvents and find one just happens to work better than another, whether its polar protic, polar aprotic, aromatic, halogenated etc.