The halide shown (axial bromine in the reactive chair) is treated with sodium azide in DMF, a good nucleophile that is only weakly basic. Which structure is the major product?

The compound is cis-1-bromo-4-methylcyclohexane. Azide is a weak base but a good nucleophile in a polar aprotic solvent, so SN2 outcompetes E2 on this secondary halide. Backside attack inverts the carbon bearing bromine, so the cis halide gives the trans-azide, trans-1-azido-4-methylcyclohexane, not the cis product (retention) or 4-methylcyclohexene.