Question

Draw the structure(s) produced by the catalytic reduction of the following compound. (H2 is in excess.) Draw hydrogen at a chirality center and use wedge-and-dash bonds to designate the stereochemistry, if applicable.

                             




Select all that apply: The alcohol product(s) of the reaction is characterized as being


_____ R,R

_____ R,S (and/or S,R)

_____ S,S

_____ achiral

_____ racemic

_____ diastereomers

_____ R

_____ S

Answer 1

Concepts and reason

The structure of a compound is given whose reduction product needs to be formed with the correct stereochemistry of the hydrogens attached. Firstly, identify whether the hydrogenation follows the syn addition or anti-addition then, write the product accordingly.

Fundamentals

The hydrogenation of alkene, that is, the addition of hydrogen to the alkene on metal surface follows syn addition. In syn addition, the addition of the group occurs from the same side as shown below:

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 product of the catalytic reduction with the correct stereochemistry following the syn addition as shown below:

Consider the products formed and mark the stereocentres whose stereochemistry needs to be assigned as shown below:

Assign R and S to the product obtained as shown below:

Now, categorize whether the products of the reaction lead to the racemic mixture, single enantiomer, achiral molecule, or diastereomers according the stereochemistry defined for the product as shown below:

As the product is the mixture of two enantiomers, that is, having R, S and S, R descriptors, hence, the products formed categorized as, racemic mixture.

Ans: