Which of the following molecule (s) have dipole moment
(I) Trans -pent -2-ene
(II) cis-hex -3-ene
(III) 2,2-Dimethy1 propane
(IV) `2,2,3,3` tetramethy1 butane .

Explanation

To determine which of the given molecules have a dipole moment, we need to analyze the molecular structure and symmetry of each compound. Here’s a step-by-step solution:

### Step 1: Analyze Trans-Pent-2-ene
- **Structure**: Trans-pent-2-ene has a double bond between the second and third carbon atoms with different groups attached to each carbon.
- **Dipole Moment**: The molecule is not symmetrical due to the different substituents on either side of the double bond. Therefore, the dipole moments from the different bonds do not cancel out.
- **Conclusion**: Trans-pent-2-ene has a dipole moment.

### Step 2: Analyze Cis-Hex-3-ene
- **Structure**: Cis-hex-3-ene also has a double bond between the third and fourth carbon atoms with similar groups on one side and different groups on the other.
- **Dipole Moment**: The presence of different groups leads to a net dipole moment that does not cancel out, as the molecule is not symmetrical.
- **Conclusion**: Cis-hex-3-ene has a dipole moment.

### Step 3: Analyze 2,2-Dimethylpropane
- **Structure**: 2,2-Dimethylpropane has a tetrahedral geometry with all carbon atoms and substituents arranged symmetrically.
- **Dipole Moment**: The symmetry in the structure means that the dipole moments from the bonds cancel each other out.
- **Conclusion**: 2,2-Dimethylpropane has no dipole moment (dipole moment = 0).

### Step 4: Analyze 2,2,3,3-Tetramethylbutane
- **Structure**: 2,2,3,3-Tetramethylbutane is also a highly branched molecule with a symmetrical structure.
- **Dipole Moment**: Similar to 2,2-Dimethylpropane, the symmetry results in the cancellation of dipole moments.
- **Conclusion**: 2,2,3,3-Tetramethylbutane has no dipole moment (dipole moment = 0).

### Final Conclusion
Based on the analysis:
- **Molecules with Dipole Moment**:
- (I) Trans-pent-2-ene
- (II) Cis-hex-3-ene
- **Molecules without Dipole Moment**:
- (III) 2,2-Dimethylpropane
- (IV) 2,2,3,3-Tetramethylbutane