Question

Draw the major organic product of the reaction. Indicate the stereochemistry via wedge/dash bonds, including explicit H and D atoms, at the stereogenic center. Omit byproducts such as salts or methanol. NaOCH3 CH3OH

Answer 1

Concepts and reason

A compound is given with the reagents added to the reaction and products needs to be written. Firstly, find the suitable reaction mechanism that the given compound would undergo to form the correct product of the reaction.

Also, the stereo center present in the reactant molecule and that formed in product molecule needs to be assigned as R and S. 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.

Fundamentals

Alkyl halides with the base can react to form a series of product based the mechanism followed, that is, either substitution or elimination product. The structure of the alkyl halide and the strength of base determine the mechanism to be followed and the formation of the suitable product. Generally, a secondary haloalkane in the presence of a sterically less hindered base follows substitution mechanism.

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

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

2.Then, compare the atomic number of the atom attached to the stereo center. 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 stereo center 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.

Identify the structure of haloalkane and the strength of base to find the reaction mechanism followed by the given reactant as shown below:

As the given structure of the haloalkane is primary and the nucleophile is less hindered, therefore, the substitution $\left( {{\rm{S}}{{\rm{N}}_{\rm{2}}}} \right)$ mechanism will be followed by the given compound

Write the product of the reaction following the ${\rm{S}}{{\rm{N}}_{\rm{2}}}$ substitution reaction mechanism as shown below:

Assign the priority to the groups attached to the chiral center resent in the organic substrate as well as in organic product of the reaction as shown below:

Hence, the descriptor for the organic substrate is ‘R’ and for organic product is ‘S’.

Ans:

the major organic product of the reaction is as follows:

Hence, the correct R and S designation to the given organic substrate and the product formed is shown below: