Chapter 6: Q35P (page 263)

What characteristics must the reactant of a stereospecific reaction have?

Short Answer

Expert verified

Answer-For a stereospecific reaction, the reactant must have the E and Z or R and S configuration.

Step by step solution

Definition of stereospecific-

If the reactant can exist as stereoisomers, and each stereoisomer of the reactant generates a different stereoisomer or set of stereoisomers of the product, the reaction is stereospecific.

stereospecific reactions-

Assigning E and Z configuration-

The IUPAC preferred technique of representing the absolute stereochemistry of double bonds in organic chemistry is the E–Z configuration, sometimes known as the E–Z convention.

Each substituent on a double bond is given a priority according to the Cahn–Ingold–Prelog priority rules (CIP rules), and then the positions of the higher of the two substituents each carbon is compared to the next.

The bond is assigned the configuration E (from entgegen, the German term for "opposite") if the two groups of higher priority are on opposite sides of the double bond (trans to each other). When the two higher priority groups are on the same side of a double bond (cis to each other), the bond is given the configuration Z (from zusammen], the German term for "together").

Assigning R and S configuration-

Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and the stereochemical description that results.

When carbon is linked to four separate substituents in organic compounds, absolute configuration is important. Absolute configuration describes the relative positions of each bond around the chiral centre atom using a set of criteria.

The Cahn–Ingold–Prelog priority principles are used in the most common labelling approach, which uses the descriptors R or S. Rectus and Sinister are Latin words that mean right and left, respectively.

When the centre is oriented so that the lowest-priority substituent of the four is facing the viewer, the viewer will see two options: if the priority of the remaining three substituents decreases clockwise, it is labelled R (for Rectus, Latin for right); if it decreases anticlockwise, it is labelled S. (for Sinister, Latin for left).