Identify the correct order of boiling points of the following compounds
(I) `CH_3CH_2CH_2CH_2OH`
(II) `CH_3CH_2CH_2CHO`
(III) `CH_3CH_2CH_2COOH`

Options

A. `I gt II gt III`
B. `III gt I gt II`
C. `I gt III gt II`
D. `III gt II gt I`

Answer

To determine the correct order of boiling points of the given compounds, we need to analyze the functional groups present in each compound and their ability to form hydrogen bonds. The compounds are as follows:

1. **(I) CH₃CH₂CH₂CH₂OH** - This is a straight-chain alcohol (butanol).
2. **(II) CH₃CH₂CH₂CHO** - This is a straight-chain aldehyde (butanal).
3. **(III) CH₃CH₂CH₂COOH** - This is a straight-chain carboxylic acid (butanoic acid).

### Step 1: Identify the Functional Groups
- **Butanol (I)** has an -OH (hydroxyl) group which allows for hydrogen bonding.
- **Butanal (II)** has a -CHO (carbonyl) group which can participate in dipole-dipole interactions but does not form hydrogen bonds as effectively as alcohols or carboxylic acids.
- **Butanoic acid (III)** has a -COOH (carboxyl) group which can form strong hydrogen bonds due to the presence of both a carbonyl and a hydroxyl group.

### Step 2: Evaluate Hydrogen Bonding
- **Butanoic acid (III)**: Strong hydrogen bonding due to the -COOH group. Carboxylic acids generally have higher boiling points because they can form dimers through hydrogen bonding.
- **Butanol (I)**: Moderate hydrogen bonding due to the -OH group. Alcohols also have higher boiling points than aldehydes due to hydrogen bonding.
- **Butanal (II)**: Weaker intermolecular forces compared to the other two compounds, as it primarily relies on dipole-dipole interactions.

### Step 3: Compare Boiling Points
Based on the strength of hydrogen bonding and the type of intermolecular forces:
- **Butanoic acid (III)** will have the highest boiling point due to strong hydrogen bonding.
- **Butanol (I)** will have a lower boiling point than butanoic acid but higher than butanal due to its ability to form hydrogen bonds.
- **Butanal (II)** will have the lowest boiling point as it relies mainly on dipole-dipole interactions.

### Conclusion: Order of Boiling Points
Thus, the correct order of boiling points from highest to lowest is:
**(III) > (I) > (II)**