Which of the following compounds have finite dipole moments ?

Options

A. trans-2-Pentene
B. cis-2-Pentene
C. 1-Butyne
D. 2-Butyne

Answer

To determine which of the given compounds have finite dipole moments, we need to analyze the molecular structures and the symmetry of each compound. A finite dipole moment occurs when there is an uneven distribution of electron density across a molecule, leading to a positive and a negative end.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We need to analyze the following compounds:
- Trans-2-pentene
- Cis-2-pentene
- But-1-yne
- 1,3-butadiene

2. **Analyze Trans-2-pentene**:
- Structure: CH3-CH=CH-CH3 (with the two CH3 groups on opposite sides).
- Symmetry: The molecule is not symmetrical due to the presence of the double bond and the different groups attached to the carbon atoms.
- Dipole Moment: The dipole moments from the different groups do not cancel out, resulting in a finite dipole moment.

3. **Analyze Cis-2-pentene**:
- Structure: CH3-CH=CH-CH3 (with the two CH3 groups on the same side).
- Symmetry: Similar to trans-2-pentene, this compound is also asymmetrical.
- Dipole Moment: The dipole moments do not cancel out, leading to a finite dipole moment.

4. **Analyze But-1-yne**:
- Structure: CH3-CH2-C≡C-H.
- Symmetry: The molecule has a triple bond and is asymmetrical due to the different groups attached.
- Dipole Moment: The dipole moment does not cancel out, resulting in a finite dipole moment.

5. **Analyze 1,3-butadiene**:
- Structure: CH2=CH-CH=CH2.
- Symmetry: This compound is symmetrical, with equal electron distribution.
- Dipole Moment: The dipole moments cancel out, resulting in a net dipole moment of zero.

6. **Conclusion**:
- The compounds with finite dipole moments are:
- Trans-2-pentene
- Cis-2-pentene
- But-1-yne
- The compound with no finite dipole moment is 1,3-butadiene.

### Final Answer:
The compounds that have finite dipole moments are **Trans-2-pentene, Cis-2-pentene, and But-1-yne**.

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