Final answer:
The hydrosulfide ion, when attacking a chiral center, results in an inversion of configuration at that center as part of an SN2 reaction.
Step-by-step explanation:
When the hydrosulfide ion (HS-) from NaSH attacks a chiral center, it acts as a nucleophile in an SN2 reaction, resulting in the inversion of configuration at the chiral center. This can lead to a change from an (R)-enantiomer to an (S)-enantiomer or vice versa. The nucleophilic attack occurs as the leaving group departs in one concerted step, passing through a transition state where the chiral center becomes planar before forming the product with inverted stereochemistry.
In an SN2 reaction, the nucleophile attacks from the side opposite to the leaving group, causing what is known as a 'backside attack'. This results in the inversion of the configuration at the chiral center, as if an umbrella were being turned inside out. The new configuration is the stereoisomer (enantiomer) of the original configuration before the reaction.
To predict the product configuration, priority is assigned based on the atomic number of the atoms attached to the chiral center. For example, if the priorities are -NH2 (1), -C(CH3)2SH (2), -COOH (3), and -H (4), the configuration after SN2 will be determined by the placement of these groups relative to the new bond formed with the hydrosulfide ion.