The halide shown is converted to its Grignard reagent with magnesium in dry ether; heavy water ($\mathrm{D}{}_2\mathrm{O}$) is then added. Which structure is the main organic product?

The carbon-magnesium bond is protonated (here deuterated) by D2O exactly where magnesium was bound, with no rearrangement. 2-Bromobutane gives 2-deuteriobutane, a chiral isotopologue formed as a racemate. Butane is formed if H2O is used, butan-2-ol requires oxygen, and 1-deuteriobutane would require a shift of the metal.