The major product formed during the hydroboration-oxidation of 1-methyl cyclopentene is (B) 1-methylcyclopentanol.
Hydroboration-oxidation is a chemical reaction that converts an alkene or alkyne into an alcohol or ketone. The reaction is carried out in two steps:
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Hydroboration. In the first step, the alkene or alkyne is reacted with borane, $\ce{BH3}$. The borane adds to the alkene or alkyne in a syn fashion, forming a trialkylborane.
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Oxidation. In the second step, the trialkylborane is oxidized with hydrogen peroxide, $\ce{H2O2}$. This oxidation converts the trialkylborane into an alcohol or ketone.
In the case of 1-methyl cyclopentene, the hydroboration step produces the trialkylborane 1-methylcyclopentaneborane. The oxidation step then converts this trialkylborane into the alcohol 1-methylcyclopentanol.
The other options are incorrect because they do not represent the major product of the hydroboration-oxidation of 1-methyl cyclopentene. Option A, 1-methylcyclopentene, is the starting material. Option C, 1-methylcyclopentanone, is a possible product, but it is not the major product. Option D, 1-methylcyclopentene-1,2-diol, is not a possible product of the hydroboration-oxidation reaction.