The problem asks to identify the major products A and B formed from the reaction of 1-methylcyclohexene under two different conditions: acid-catalyzed hydration and hydroboration-oxidation.
Concept Used:
The reactions shown are two common methods for the hydration of alkenes, which yield different constitutional isomers depending on the mechanism and regioselectivity.
1. Acid-Catalyzed Hydration (H+/H2O): This reaction proceeds via the formation of a carbocation intermediate. The addition of water follows Markovnikov's rule, which states that the hydrogen atom adds to the carbon of the double bond that has more hydrogen atoms, and the hydroxyl group (-OH) adds to the carbon that has fewer hydrogen atoms (the more substituted carbon). This pathway leads to the formation of the more stable carbocation intermediate.
2. Hydroboration-Oxidation (B2H6, then H2O2, NaOH): This is a two-step process that results in the net addition of water across the double bond. The reaction proceeds via a concerted syn-addition of borane (BH3), followed by an oxidation step. The regioselectivity is anti-Markovnikov, meaning the hydroxyl group (-OH) adds to the less substituted carbon atom of the double bond.
Step 1: Formation of Product A (Acid-Catalyzed Hydration)
The starting material is 1-methylcyclohexene. In the presence of acid (H+), the double bond is protonated. According to Markovnikov's rule, the proton adds to the less substituted carbon of the double bond (C-2) to generate the more stable carbocation, which is a tertiary carbocation at C-1.
The water molecule then acts as a nucleophile and attacks the tertiary carbocation. A final deprotonation step yields the product A, which is 1-methylcyclohexan-1-ol.
Product A is 1-methylcyclohexan-1-ol.
Step 2: Formation of Product B (Hydroboration-Oxidation)
This reaction follows the anti-Markovnikov rule. In the first step (hydroboration), the borane (BH3) adds across the double bond. The boron atom, being the less electronegative part, adds to the less sterically hindered and less substituted carbon (C-2), while the hydrogen atom adds to the more substituted carbon (C-1). This addition is a syn-addition.
In the second step (oxidation), the C-B bond is replaced by a C-OH bond with retention of stereochemistry. The net result is the addition of an -OH group to the less substituted carbon atom.
The final product B is 2-methylcyclohexan-1-ol.
Product B is 2-methylcyclohexan-1-ol.
Step 3: Matching the Products with the Options
We have identified:
Product A = 1-methylcyclohexan-1-ol
Product B = 2-methylcyclohexan-1-ol
Comparing these structures with the given options, we find that option (2) correctly identifies both products.
Therefore, the correct option is (2).
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Approach Solution -2
The reaction shown indicates the process of hydrolysis and reduction of boranes. When B4H6 reacts with water and sodium hydroxide, it undergoes hydrolysis to produce alcohols and alkanes.
Understanding the Reactions: B4H6 is a borane compound, and its reaction with water in the presence of a base leads to the formation of organic products. The primary reactions involve the cleavage of the B-H bonds and subsequent formation of C-H and C-O bonds.
Products Formed: From the reaction conditions, it is clear that the product A formed from the hydrolysis will likely be a simple alcohol (such as methanol), while product B will be the corresponding alkane (like methane).
Thus, the correct identification of products A and B leads to: A = CH3, B = CH2OH
