Question

What stereoisomers are obtained from hydroboration-oxidation of $ 1 $ -ethyl cyclohexene?

Answer 1

Hint: $ 1 $ -ethyl cyclohexene is a cycloalkene in which ethyl group is substituted at the $ {C_1} $ carbon. Hydroboration-oxidation reaction is the addition of boron trihydride to an alkene further the addition of hydroxide replaces the $ B{H_2} $ group and substitutes the hydroxyl group. Different isomers were obtained when hydroboration-oxidation of $ 1 $ -ethyl cyclohexene is done.

Complete answer:
Stereoisomers are the chemical compounds that contain the same molecular formula, but there is a difference of direction of arrangement of atoms or groups in the molecule.
 $ 1 $ -ethyl cyclohexene is a cycloalkene in which an ethyl group is substituted at the $ {C_1} $ carbon. Hydroboration is the reaction of addition of simple boranes like $ B{H_3} $ to alkene, which results in the addition of $ H $ and $ B{H_2} $ units leading to the formation of alkyl boranes.
Later this alkyl boranes when treated with hydrogen peroxide which is an oxidation reaction leads to the formation of alcohols as $ B{H_2} $ is replaced by hydroxide ion from hydrogen peroxide. There is no formation of intermediates as only the transition state was formed.
The hydroboration-oxidation of $ 1 $ -ethyl cyclohexene is:

Though the formed two products are with the same molecular formula, there is a difference in the arrangement of groups that leads to the formation of stereoisomers.
The product $ 1 $ is $ \left( {1S,2R} \right) - 2 - ethylcyclohexanol $
The product $ 1 $ is $ \left( {1R,2S} \right) - 2 - ethylcyclohexanol $ .

Note:
The overall reaction favours the anti-markovnikov's rule as the hydroxide group is attached to the carbon containing more number of hydrogen atoms. The addition of borane favours the syn-addition as both $ H $ and $ B{H_2} $ units were added at the same side of the double bond.