Question

Chemistry Organic 1 C306 01 Assignment 05, spring 2019 Answer All Questions. Consider the following pairs of structures. Identify the relationship between them by 1. describing them as representing enantiomers, diastereomers, constitutional isomers, or two molecules of the same compound. CH3 CH3 a. HBr and Br CH3 b. and BrH H Br CH3 C. Br and CH3 CH3 d. Br СНу and CH3 CH3 e. Br an CH3 f. CH3 CH3 Brand H CH3 . Lindane (hexachl orocyclohex.ane) is an agricultural insectici de that can also be used in the treatment of head lice. The skel eton of the two chair conform ati ons has been drawn Place each substituent(s) in the correct loc ati on with the correct configurati on. Cl Draw the enantiom er for each of the following compounds 4 Cl OH a. nus b.

Answer 1

The absolute configuration of a molecule around its chiral center is designated by the direction of arrangement of the groups in the descending order of priority. The priorities of the groups/atoms directly attached to the chiral carbon is given by the Cahn-Ingold-Prelog rules which dictate higher atomic numbers to have higher priorities.

If the arrangement of groups in the Fischer projection of the molecule go clockwise when going from the highest to lowest group, the configuration is R. If the groups go counter-clockwise, it is S as long as the group of least priority is either at the top or at the bottom. If however, the lowest priority group is to the left or right in the projection, the configuration obtained as such is reverse of the absolute configuration.

Chiral compounds are those which are identical in molecular formula, functional groups and linkages but differ in the arrangement of groups around the chiral centers, in three-dimensional space. Among enantiomers, the configuration at the chiral center(s) of all the centers are opposite to one another while in a diastereomer, not all chiral centers' absolute configuration is the opposite of each other. So, a molecule having only one chiral center can only have enantiomer while a molecule with more than one can have enantiomers as well as diastereomers.

a) Br has the highest priority, followed by F, followed by methyl and finally H. So, both the molecules have the configuration S, making them identical.

b) The configurations of the molecules are S and R respectively, which make them opposites in configurations. This is therefore a pair of enantiomers.

c) The configurations of these are (S, S) and (R, S) respectively. Since only center is the opposite, this is a pair of diastereomers.

d) The configurations of these molecules are also (S, S) and (R, S) respectively making this set also diastereomers.

e) The configurations of this pair are (S, R) and (R, S) respectively. Since both the chiral centers' configurations are opposites, this is a pair of enantiomers.

f) Here, the very order of linkage of atoms has changed and so are no more identical in every way except their orientation in space. So, this is a pair of constitutional isomers.