As `S_(N^(2))` reaction at an asymmetric carbon of a compound always gives:

Options

A. An enantiomer of the substrate
B. A product with opposite optical rotation
C. A mixture of diasteromers
D. A product with 100% inversion

Answer

To answer the question regarding what an \( S_N2 \) reaction at an asymmetric carbon of a compound always gives, we will analyze the characteristics of the \( S_N2 \) mechanism step by step.

### Step 1: Understanding \( S_N2 \) Mechanism
The \( S_N2 \) (Substitution Nucleophilic Bimolecular) reaction involves a nucleophile attacking the electrophilic carbon atom from the opposite side of the leaving group. This backside attack leads to a transition state where the nucleophile and the leaving group are both partially bonded to the carbon.

**Hint:** Remember that in \( S_N2 \) reactions, the nucleophile attacks from the opposite side of the leaving group.

### Step 2: Inversion of Configuration
When the nucleophile attacks the asymmetric carbon, it causes the configuration of the carbon to invert. This means that if the original configuration was R (rectus), the product will be S (sinister), or vice versa. This is known as Walden inversion.

**Hint:** Focus on how the configuration changes due to the backside attack of the nucleophile.

### Step 3: Formation of a Single Product
In \( S_N2 \) reactions, only one product is formed due to the specific nature of the reaction mechanism. This product will have the opposite stereochemistry compared to the starting material.

**Hint:** Recall that \( S_N2 \) reactions do not lead to a mixture of products; they produce a single stereoisomer.

### Step 4: Analyzing the Options
Now, let's analyze the provided options based on our understanding:
1. **An enantiomer of a substrate is formed** - This is incorrect; while an enantiomer is a type of stereoisomer, the \( S_N2 \) reaction specifically results in inversion.
2. **A product with opposite optical rotation is formed** - This is correct; the product will have an opposite optical rotation due to the inversion.
3. **A mixture of diastereomers is formed** - This is incorrect; \( S_N2 \) does not produce diastereomers.
4. **A product with 100% inversion is formed** - This is also correct; the reaction results in complete inversion of configuration.

### Conclusion
Thus, the correct answers are:
- A product with opposite optical rotation is formed.
- A product with 100% inversion is formed.

### Final Answer
The \( S_N2 \) reaction at an asymmetric carbon of a compound always gives a product with opposite optical rotation and a product with 100% inversion.