Question

The product of acid-catalysed hydration of 2 -phenyl propene is (1) 3-phenyl-2-propanol (2) I-phenyl-2-propanol (3) 2-phenyl-2-propanol (4) 2-phenyl-1-propanol

Short answer

The product is 2-phenyl-2-propanol (Option 3).

Step-by-step solution

- Understand the reaction

Acid-catalyzed hydration involves adding water (H₂O) across a double bond in the presence of an acid (usually H₂SO₄ or H₃O⁺).

- Identify the alkene

The given molecule is 2-phenylpropene, which has the structure:

- Markovnikov's Rule

According to Markovnikov's rule, the hydrogen atom (from water) will add to the carbon with the most hydrogen atoms already attached, and the hydroxyl group (OH) will add to the carbon with the least hydrogen atoms.

- Determine the product

In 2-phenylpropene, the double bond is between the second and third carbon atoms. The hydrogen will add to the third carbon atom, and the hydroxyl group will add to the second carbon atom.

- Naming the product

The product will be 2-phenyl-2-propanol because the hydroxyl group is attached to the second carbon atom.

Key concepts

Markovnikov's Rule

Markovnikov's Rule is a guiding principle in organic chemistry for predicting the outcome of addition reactions involving alkenes. It states that when adding particles like hydrogen halides (HX) or water (H₂O) to an alkene, the hydrogen (H) adds to the carbon that already has the most hydrogen atoms. Meanwhile, the other part of the adding molecule, like a halide (X) or hydroxyl group (OH), attaches to the carbon with fewer hydrogen atoms.

This rule helps us understand why certain products form during acid-catalyzed hydration. By following Markovnikov's Rule, you can predict the major product of these reactions accurately. Remember, this rule applies due to the stability of intermediates formed during the reaction.

Alkene

An alkene is an organic compound that contains at least one carbon-carbon double bond (C=C). These double bonds are reactive sites for various chemical reactions, including acid-catalyzed hydration.

When looking at alkenes, the double bond represents a region of high electron density, making it an attractive target for electrophilic addition reactions. For example, in the presence of an acid, a water molecule can add across the double bond, leading to hydration. Understanding the nature of alkenes is key to predicting how they will react and what products they will form.

2-phenylpropene

2-phenylpropene, also known as isobutylene, is an alkene with the chemical structure C₆H₅CH=CHCH₃. The '2-phenyl' part indicates a phenyl group (C₆H₅) attached to the second carbon in the propene chain.

Given its structure, the double bond is between the second and third carbon atoms. During acid-catalyzed hydration of 2-phenylpropene, water adds across this double bond. According to Markovnikov's Rule, the hydrogen (H) from water attaches to the third carbon, while the hydroxyl group (OH) attaches to the second carbon. This leads to the formation of 2-phenyl-2-propanol as the main product.

Organic Reaction Mechanism

Understanding the organic reaction mechanism is crucial for predicting reaction products. In acid-catalyzed hydration, the mechanism involves several steps:

• Protonation of the alkene to form a more stable carbocation intermediate.
• Water (acting as a nucleophile) adding to the carbocation intermediate.
• Deprotonation of the added water molecule, resulting in the formation of an alcohol.

In our example with 2-phenylpropene, the acid first protonates the double bond, forming a carbocation at the second carbon. Water then adds to this carbocation, and after losing a proton, forms 2-phenyl-2-propanol. Each step follows a logical sequence, ensuring the most stable intermediate is formed, which determines the final product.