Which of the following alcohol is least soluble in water?

Options

A. n-Butyl alcohol
B. Iso-Butyl alcohol
C. Tert-Butyl alcohol
D. Sec-Butyl alcohol

Answer

To determine which alcohol is least soluble in water, we need to consider the structure of the alcohols provided in the options and how their carbon chain length and branching affect their solubility. Here's a step-by-step solution:

### Step 1: Understand Alcohol Solubility
Alcohols are soluble in water due to hydrogen bonding. The hydroxyl (-OH) group can form hydrogen bonds with water molecules, which increases solubility.

**Hint:** Remember that the ability to form hydrogen bonds is key to solubility in water.

### Step 2: Analyze the Effect of Carbon Chain Length
As the carbon chain length increases, the hydrophobic (water-repelling) character of the carbon chain becomes more significant. This reduces the overall solubility of the alcohol in water.

**Hint:** Longer carbon chains lead to a greater hydrophobic effect, which decreases solubility.

### Step 3: Consider the Impact of Branching
Branched alcohols tend to be more soluble than their straight-chain counterparts because branching reduces the surface area that is hydrophobic. This allows for more effective hydrogen bonding with water.

**Hint:** More branching typically means better solubility due to reduced hydrophobic surface area.

### Step 4: Compare the Given Alcohols
Now, let's compare the alcohols based on their structure:
- **n-Butyl alcohol** (linear)
- **Isobutyl alcohol** (branched)
- **Sec-butyl alcohol** (branched)
- **Tert-butyl alcohol** (highly branched)

Among these, n-butyl alcohol is linear and has the longest carbon chain without branching, which gives it a larger hydrophobic surface area compared to the branched alcohols.

**Hint:** Identify which alcohol has the longest linear chain and less branching.

### Step 5: Conclusion
Based on the analysis, n-butyl alcohol will be the least soluble in water due to its linear structure and larger hydrophobic surface area compared to the branched alcohols.

**Final Answer:** n-Butyl alcohol is the least soluble in water.