Which of the following species is a carbene?

Options

A. `:CH_(3)^(-)`
B. `:C Cl_2`
C. `CH_2 =C=O`
D. `R-overset(*)CH -R`

Explanation

To determine which of the following species is a carbene, we need to understand the definition and characteristics of a carbene.

### Step-by-Step Solution:

1. **Define Carbene**: A carbene is a neutral species that contains a carbon atom with two valence electrons and has either a lone pair of electrons or two unshared electrons. It can be classified into two types: singlet carbene and triplet carbene.

2. **Identify Other Carbon Species**:
- **Carbocation**: A species with a positive charge on the carbon atom (e.g., R3C+).
- **Carbanion**: A species with a negative charge on the carbon atom (e.g., R3C-).
- **Free Radical**: A species with an unpaired electron on the carbon atom (e.g., R3C•).
- **Ketene**: A compound with a carbon-carbon double bond adjacent to a carbon-carbon double bond (e.g., R2C=C=O).

3. **Analyze the Given Options**:
- Look for a species that has a carbon atom with a lone pair of electrons or two unshared electrons.
- The species that fits this description will be classified as a carbene.

4. **Select the Correct Answer**:
- Among the options provided, identify which one represents a carbene. The correct answer will be the species that has a carbon atom with a lone pair of electrons.

5. **Conclusion**: The species that is identified as a carbene is dichlorocarbene, which has a carbon atom with a lone pair of electrons.

### Final Answer:
The species that is a carbene is **dichlorocarbene**.

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