Acetic acid exists as dimer in benzene due to

Options

A. a condensation reaction
B. hydrogen bonding.
C. presence of carbonyl group
D. presence of hydrogen atom at `alpha`-carbon atom.

Answer

To understand why acetic acid exists as a dimer in benzene, we can break down the explanation into several steps:

### Step 1: Understanding Acetic Acid Structure
Acetic acid (CH₃COOH) consists of a methyl group (CH₃) attached to a carboxylic acid group (COOH). The carboxylic acid group contains a carbonyl (C=O) and a hydroxyl (O-H) functional group.

### Step 2: The Role of Hydrogen Bonding
In benzene, acetic acid molecules can interact with each other through hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like oxygen) experiences an attraction to another electronegative atom.

### Step 3: Formation of the Dimer
When two acetic acid molecules come into proximity in benzene, the oxygen atom of one acetic acid molecule can donate its lone pair of electrons to the hydrogen atom of the hydroxyl group of another acetic acid molecule. This interaction leads to the formation of a hydrogen bond.

### Step 4: Visualization of the Dimer
As a result of these hydrogen bonds, two acetic acid molecules can link together, forming a dimer. The structure can be represented as:
- One acetic acid molecule donates its lone pair from the oxygen to the hydrogen of another acetic acid molecule, creating a stable dimeric structure.

### Step 5: Conclusion
Thus, the presence of hydrogen bonding between acetic acid molecules in benzene is the reason why acetic acid exists as a dimer in this solvent.

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