5-chloro-1, 3 - dimethylcyclohexene is the substrate. I understand that hydroboration oxidation occurs in 2 steps the first being addition of Boron as an electrophile and the second being oxidation by peroxide ion. Since the solution now contains Hydroxide ion now this will attack the carbon bonded to chlorine by SN2 mechanism. But in my book , in the final product chlorine is not replaced with OH. I don't understand why.
OH- is not that great a nucleophile for a secondary chloride.
If we assume an ethereal solvent, most likely THF, much of the OH- will be in aqueous phase and not available to react with the product in the organic phase. If the reaction is kept cool (as it should be) E2 is unlikely to be a major pathway hence the product is 5-chloro-1,3-dimethylcyclohexan-2-ol