$C{H}_3-CH=C{H}_2\underset{\left(ii\right)H_2{O}_2,O{H}^{-}}{\overset{\left(i\right)B{H}_3.THF}{\to }}C{H}_{3}C{H}_{2}C{H}_{2}OH$
Number of moles of alkenes used in the complete reaction is…………………

Hydroboration-Oxidation Reaction

1. Hydroboration (Step 1):

• Reagent Used: Borane (BH3) in tetrahydrofuran (THF).
• The alkene (CH3CH = CH2) undergoes hydroboration, where borane (BH3) adds across the double bond in an anti-Markovnikov manner.
• Boron attaches to the less substituted carbon atom, while hydrogen attaches to the more substituted carbon atom.

Reaction:

3CH3CH=CH2 + BH3 → B(CH2CH2CH3)3

Here, one molecule of borane reacts with three molecules of the alkene.

2. Oxidation (Step 2):

• Reagents Used: Hydrogen peroxide (H2O2) and hydroxide (OH-).
• The boron group (B(CH2CH2CH3)3) is oxidized to form the corresponding alcohols (CH3CH2CH2OH).
• The hydroxyl group replaces the boron atom.

Reaction:

B(CH2CH2CH3)3 + 3H2O2/OH- → 3CH3CH2CH2OH + H3BO3

The by-product is boric acid (H3BO3).

Number of Moles of Alkenes Used:

From the balanced reaction, one mole of borane (BH3) reacts with three moles of alkene. This is because each boron atom can form three bonds with alkene molecules.

• Step 1 (Hydroboration): Three moles of CH3CH=CH2 react with one mole of BH3.
• Step 2 (Oxidation): The product from step 1 is oxidized to produce three moles of alcohol (CH3CH2CH2OH).

Therefore, the total number of moles of alkenes used is 3.

Concepts Behind the Answer:

• Anti-Markovnikov Addition: In hydroboration, boron adds to the less substituted carbon, and hydrogen adds to the more substituted carbon of the double bond.
• Stoichiometry: One molecule of BH3 reacts with three molecules of alkene, leading to a 1:3 ratio.
• Oxidation with Hydrogen Peroxide: The boron group is replaced by a hydroxyl group, forming the alcohol.

By understanding these principles, the number of moles of alkenes used in the complete reaction can be calculated accurately.