The hyperconjugative stabilities of tert-butyl cation and 2-butene, respectively, are due to

Options

A. `sigma to p` (empty) and `sigma to pi^(**)` electron delocalisations
B. `sigma to sigma " and " sigma to pi^(**)` electron delocalisations
C. `sigma to p` (filled) and `sigma to pi^(**)` electron delocalisations
D. p (filled ) `to sigma " and " sigma to pi^(**)` electron delocalisations

Answer

To determine the hyperconjugative stabilities of the tert-butyl cation and 2-butene, we need to analyze the structures and the types of hyperconjugation involved in each case.

### Step-by-Step Solution:

1. **Understanding Tert-Butyl Cation Structure**:
- The tert-butyl cation (C4H9+) has the following structure:
```
CH3
|
CH3-C^+
|
CH2
```
- In this structure, the central carbon (C+) carries a positive charge, making it a carbocation.

2. **Hyperconjugation in Tert-Butyl Cation**:
- Hyperconjugation involves the interaction between the empty p-orbital of the carbocation and the adjacent C-H sigma bonds.
- The three methyl groups (CH3) attached to the cation can donate electron density through their C-H sigma bonds to the empty p-orbital of the carbocation.
- This stabilizes the cation due to the delocalization of charge, making the tert-butyl cation more stable.

3. **Understanding 2-Butene Structure**:
- The structure of 2-butene (C4H8) is:
```
H H
\ /
H-C=C-H
/ \
H CH3
```
- In this structure, there is a double bond between two carbon atoms.

4. **Hyperconjugation in 2-Butene**:
- In 2-butene, hyperconjugation occurs due to the interaction of the pi bond (C=C) with adjacent C-H sigma bonds.
- The pi electrons can delocalize into the adjacent C-H sigma bonds, leading to stabilization through what is known as pi-sigma star conjugation.
- This delocalization of electrons contributes to the stability of the double bond in 2-butene.

5. **Identifying the Correct Answer**:
- The question asks for the hyperconjugative stabilities of tert-butyl cation and 2-butene.
- The correct answer is that the stability of the tert-butyl cation arises from sigma p hyperconjugation, while the stability of 2-butene arises from sigma pi star hyperconjugation.
- Thus, the correct option is "sigma p and sigma pi star."

### Final Answer:
The hyperconjugative stabilities of tert-butyl cation and 2-butene, respectively, are due to sigma p hyperconjugation and sigma pi star hyperconjugation.