Illustrated Glossary of Organic Chemistry

No reaction (NR): A circumstance in which mixing of reactants causes no change in molecular structure. Frequently abbreviated as NR.

No reaction
Tert-butyl chloride does not react with cyanide ion (a nucleophile) in acetone (a nonpolar aprotic solvent) because chloride (the leaving group) is bonded to a tertiary carbon, and there is too much steric hindrance for the SN2 mechanism to occur.