Which of the following cannot exhibit hypercojugation -

Options

A. `CH_(3)overset(.)CH_(2)`
B. `(CH_(3))_(2)overset(+)CH`
C. `CH_(3)CH=CH_(2)`
D. `(CH_(3))_(3)C-overset(+)C-CH_(2)`

Answer

To determine which of the given molecules cannot exhibit hyperconjugation, we need to understand the concept of hyperconjugation and identify the presence of alpha hydrogens in each molecule.

### Step-by-Step Solution:

1. **Understand Hyperconjugation**:
Hyperconjugation is the delocalization of electrons in sigma bonds (typically C-H or C-C bonds) with adjacent empty or partially filled p-orbitals or pi-orbitals. This effect stabilizes the molecule.

2. **Identify Alpha Hydrogen**:
An alpha hydrogen is a hydrogen atom attached to the alpha carbon, which is the carbon adjacent to a carbon that has a double bond, positive charge, or radical. If an alpha carbon has no hydrogen atoms attached, hyperconjugation cannot occur.

3. **Analyze Each Molecule**:
- **Molecule 1: CH3-CH2• (Radical)**:
- The alpha carbon (CH2) has three hydrogens.
- **Conclusion**: Hyperconjugation is possible.

- **Molecule 2: (CH3)2C+ (Carbocation)**:
- The alpha carbon (C) has two hydrogens attached.
- **Conclusion**: Hyperconjugation is possible.

- **Molecule 3: CH3-CH=CH2 (Alkene)**:
- The alpha carbon (CH) has two hydrogens attached.
- **Conclusion**: Hyperconjugation is possible.

- **Molecule 4: (CH3)3C+ (Tertiary Carbocation)**:
- The alpha carbon (C) has no hydrogens attached (all are replaced by methyl groups).
- **Conclusion**: Hyperconjugation is NOT possible.

4. **Final Answer**:
The molecule that cannot exhibit hyperconjugation is **(CH3)3C+** (option D).