An SN2 reaction at asymmetric carbon of a compound always gives a single stereoisomer.

Explanation:

SN2 Reaction:
The term SN2 stands for Substitution Nucleophilic Bimolecular. It is a type of nucleophilic substitution reaction in which a nucleophile replaces a leaving group in an organic compound. The reaction occurs in one step with the nucleophile attacking the carbon center and the leaving group leaving simultaneously.

Asymmetric Carbon:
An asymmetric carbon or chiral carbon is a carbon atom that is bonded to four different substituents. It is also known as a stereogenic center because it has the ability to create stereoisomers. Stereoisomers are molecules that have the same molecular formula and connectivity but differ in the spatial arrangement of their atoms.

SN2 Reaction at Asymmetric Carbon:
When an SN2 reaction occurs at an asymmetric carbon, the nucleophile attacks the carbon center, resulting in the formation of a new chiral center. The stereochemistry of the product is determined by the stereochemistry of the starting material and the mechanism of the reaction.

Single Stereoisomer:
The SN2 reaction at an asymmetric carbon always gives a single stereoisomer as the product. This is because the nucleophile attacks from the backside of the leaving group, causing an inversion of configuration at the chiral center. This inversion results in the formation of a single enantiomer of the product.

Explanation:
- The SN2 reaction proceeds via a backside attack, where the nucleophile approaches the carbon center from the side opposite to the leaving group.
- This backside attack causes the configuration of the chiral center to invert, resulting in the formation of a single enantiomer.
- Since the reaction proceeds via a concerted mechanism, there are no intermediates or multiple transition states that could lead to the formation of diastereomers.
- Therefore, the SN2 reaction at an asymmetric carbon always gives a single stereoisomer as the product.

In conclusion, an SN2 reaction at an asymmetric carbon of a compound always gives a single stereoisomer as the product due to the backside attack and inversion of configuration. This is an important aspect of stereochemistry in organic chemistry.