Question

Draw the structure of the product formed in the following reaction of an epoxide with ethoxide ion. If more than one stereochemical product is possible, draw only one isomer. Select an that apply The product's) of the reaction are characterized as being racemic. R.R. R.S. S. R. achiral S.S.

Answer 1

Concepts and reason

A reaction is given with the reagents whose correct product needs to be formed. The reactant contains an epoxide ring and a base is acting on it, thus it will result in the opening of the epoxide ring. Hence, determine the correct product of the reaction by considering the stereochemical aspects of the reaction as well by using CIP rules.

Fundamentals

Epoxide also known as cyclic ethers undergoes substitution ring through ring opening mechanism. The reaction is also important from the stereochemical point of view as the cyclic ring provide hindrance for the incoming nucleophile and therefore, the attack takes place from the other place.

The rules for assigning the R, S configuration are as follows:

• Identify the chiral center and assign priorities to the atoms based on its atomic number. The atom which has highest atomic number gets the first priority and atom which has least atomic number (usually hydrogen) fourth priority.

• The higher atomic mass receives higher priority.

• If the first atom of each substituent is same then give priority to the second atom in each substituent.

• If the substituents have multiple bonds, the multiple bonded atoms are considered as same number of single boned atoms. The rules for assigning the R, S configuration are as follows:

• Identify the chiral center and assign priorities to the atoms based on its atomic number. The atom which has highest atomic number gets the first priority and atom which has least atomic number (usually hydrogen) fourth priority.

• The higher atomic mass receives higher priority.

• If the first atom of each substituent is same then give priority to the second atom in each substituent.

• If the substituents have multiple bonds, the multiple bonded atoms are considered as same number of single boned atoms.

• When the priority is given to these groups, that is, through number 1, 2, 3, and 4 then, rotation is done from highest priority group to the lowest, that is, 1 to 2 to 3.

• If the rotation is observed as clockwise, then the descriptor is assigned as R and if the rotation is observed as anti-clockwise then, the descriptor is assigned as S.

• Also, lowest priority group should not be present above the plane, otherwise reverse the descriptor from R to S or vice-versa.

Consider the reaction of the given compound with the reagent 1, that is, ethoxide ion as shown below:

Consider the reaction of the product formed in the first step with the second reagent given in the reaction, that is, hydrogen ion as shown below:

Consider the following product and mark them as A and B as shown below:

Assign the R and S nomenclature to the two chiral centers present in both the products as mentioned above:

Hence, the product formed as enantiomer having configuration (S,S) and (R,R) configuration in product A and B respectively at both the stereocenter.

Ans:

Hence, the structure of the products formed in the given reaction is as follows: