Electronegativity of carbon atoms depends upon their state of hybridisation. In which of the following compounds, the carbon marked with asterisk is most electronegative ?

Options

A. `CH_(3) - CH_(2) - .^(**)CH_(2) - CH_(5)`
B. `CH_(3) - .^(**)CH = CH - CH_(3)`
C. `CH_(3) - CH_(2) - C -= .^(**)CH`
D. `CH_(3) - CH_(2) - CH = .^(**)CH_(2)`

Explanation

To determine which carbon atom marked with an asterisk is the most electronegative based on its hybridization, we can follow these steps:

### Step 1: Understand the Relationship Between Electronegativity and Hybridization
The electronegativity of carbon atoms is influenced by their hybridization state. The more s character a hybridized carbon has, the more electronegative it is. This is because the s orbital is closer to the nucleus, allowing it to attract electrons more effectively.

### Step 2: Identify the Hybridization Types
There are three main types of hybridization for carbon:
- **sp Hybridization**: 50% s character (1 s orbital and 1 p orbital)
- **sp² Hybridization**: 33% s character (1 s orbital and 2 p orbitals)
- **sp³ Hybridization**: 25% s character (1 s orbital and 3 p orbitals)

### Step 3: Analyze the Given Compounds
We need to analyze the carbon atoms marked with an asterisk in the given compounds and determine their hybridization:

1. **First Compound**: The carbon has four sigma bonds (two with hydrogen and two with other carbons). This indicates **sp³ hybridization**.
2. **Second Compound**: The carbon has three sigma bonds (one with hydrogen and two with other carbons) and one pi bond. This indicates **sp² hybridization**.
3. **Third Compound**: The carbon has two sigma bonds (one with hydrogen and one with another carbon) and one pi bond. This indicates **sp hybridization**.
4. **Fourth Compound**: The carbon has three sigma bonds (one with hydrogen and two with other carbons). This indicates **sp² hybridization**.

### Step 4: Compare the Electronegativity
Based on the s character:
- **sp Hybridization** (50% s character) is the most electronegative.
- **sp² Hybridization** (33% s character) is less electronegative than sp.
- **sp³ Hybridization** (25% s character) is the least electronegative.

### Step 5: Conclusion
From the analysis, the carbon marked with an asterisk in the third compound is **sp hybridized**, making it the most electronegative among the options provided.

Thus, the answer is **the carbon in the third compound (option C)**.

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