Question

Select the correct IUPAC name for the following organic substrate, including the R or S designation where appropriate, and draw the major organic product(s) for the SN1 reaction. Include wedge/dash bonds and H on a stereocenter.

The IUPAC name for the substrate is:

Answer 1

Concepts and reason

A compound are given which are undergoing ${{\rm{S}}_{\rm{N}}}1$ reaction whose IUPAC name needs to be written with the correct R or S designation. Descriptor R and S can be assigned to the centers by following the CIP rule which is based on certain criteria of giving priorities to the groups. Also, write the organic products of the reaction following the ${{\rm{S}}_{\rm{N}}}1$ reaction.

Fundamentals

${{\rm{S}}_{\rm{N}}}1$ reaction is unimolecular nucleophilic substitution reaction which takes place between a haloalkane and a nucleophile. The reaction takes place in two step through a carbocation intermediate and the reaction product are formed with both retention as well as inversion of configuration. Consider the following scheme of a ${{\rm{S}}_{\rm{N}}}1$ reaction:

In the reaction, the nucleophile can attack from the back side as well as from the front side of the reactant.

The priority to the groups attached to the stereocentre are decided by CIP sequence rules, that is, Cahn-Ingold-Prelog rules which are as follows:

1.Firstly, locate the stereocentre in the given compound and the groups attached to it.

2.Then, compare the atomic number of the atom attached to the stereocentre. Atom having the highest atomic number assigned as the highest priority and the atom having the lowest atomic number assigned as the least priority.

3.If the first atom attached on both the sides of the stereocentre is same, then the priority is assigned to the substituent based on the next atom attached to the substituent.

4.Lowest priority group should be below the plane or away from the viewer, if is it present above the plane then change the descriptor so that the actual configuration of the molecule should not change.

For instance, if the configuration of the molecule comes out as R and lowest priority group is present above the plane then change the configuration from R to S and vice versa.

5.Then, rotation in the direction of priority order, that is, from 1 to 2 to 3 is carried out.

6.If the rotation appears as clockwise then, the stereoisomer is R. If the rotation appears as anticlockwise then, the stereoisomer is S.

Write the IUPAC name of the given organic substrate by counting the number of carbon atom in the chain and identify the functional group present as shown below:

Thus, The IUPAC name of the compound is $2 - {\rm{chlorobutane}}$ .

Write the complete IUPAC name of the given organic substrate with the correct R/S designation as shown below:

Thus, the chiral center present in the given organic substrate is assigned ‘S’ descriptor.

Write the product of the given reaction by the ${{\rm{S}}_{\rm{N}}}1$ reaction as shown below:

Ans:

The complete name of the given organic substrate is shown below: