SolutionsPhysical and Bond Properties
1. Polarity
Acetonitrile (mass 41) boils at 82 °C and propane (mass 44) at −42 °C. Why?
The C≡N group is very polar (dipole moment ≈ 3.9 D) and the linear molecules attract each other strongly by dipole-dipole forces, even though they do not form hydrogen bonds with each other.
2. Solvent
Why is acetonitrile a good solvent for SN2 reactions?
It is polar and aprotic: it dissolves salts and solvates cations, but does not hydrogen-bond to anions, which stay free and very nucleophilic.