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.