Which of the following molecules has the shortest carbon-carbon single bond length ?

Options

A. `CH_(2)=CH-C-CH`
B. `CH_(2)=CH-C-=N`
C. `CH_(2)=CH-CH-O`
D. `CH_(2)=CH-CH=CH_(2)`

Answer

To determine which of the given molecules has the shortest carbon-carbon single bond length, we need to analyze the structures of the molecules provided. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Identify the Types of Bonds
First, we need to identify the types of bonds present in each molecule. Carbon can form single (σ), double (σ + π), and triple bonds (σ + 2π).

### Step 2: Understand Bond Length Trends
- **Single Bonds**: Generally, carbon-carbon single bonds are longer than double and triple bonds.
- **Double Bonds**: Carbon-carbon double bonds are shorter than single bonds due to the presence of a π bond, which pulls the atoms closer together.
- **Triple Bonds**: Carbon-carbon triple bonds are the shortest because they consist of one σ bond and two π bonds, resulting in a stronger attraction between the two carbon atoms.

### Step 3: Analyze Resonance Effects
Resonance can also affect bond lengths. When a molecule exhibits resonance, the bond character can be altered:
- If a single bond has partial double bond character due to resonance, it will be shorter than a typical single bond.
- The more resonance structures that can be drawn, the more the bond length can be reduced.

### Step 4: Compare the Molecules
Now, let’s compare the molecules:
1. **Molecule A**: Contains only single bonds.
2. **Molecule B**: Contains single and double bonds. The single bond may be slightly shorter due to the presence of the double bond.
3. **Molecule C**: Contains single bonds and resonance structures that may impart partial double bond character, leading to shorter bond lengths.
4. **Molecule D**: Contains a triple bond, which will have the shortest bond length due to the presence of two π bonds.

### Step 5: Conclusion
Based on the analysis, the molecule with the triple bond (Molecule D) will have the shortest carbon-carbon bond length due to the strong bonding interactions from both the σ and π bonds.

### Final Answer
The molecule with the shortest carbon-carbon single bond length is the one that contains a triple bond.

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