A pharmaceutical chemist wants to synthesise a series of structural isomers of molecular formula C6H14O\text{C}_6\text{H}_{14}\text{O}C6H14O via the reduction of carbonyl precursors using sodium tetrahydridoborate(III), NaBH4\text{NaBH}_4NaBH4, in aqueous methanol.
Which of the following isomers cannot be synthesised by this route?
3,3-dimethylbutan-2-ol
2-methylpentan-2-ol
3,3-dimethylbutan-1-ol
3-methylpentan-2-ol