Question

Give the definitions of all of the following with one example for parts (1), (11),(iii), (iv): (1) Enantiomers (ii) Diastereomers (iii) Meso compound (iv) Achiral molecule (v) Optical Activity

Answer 1

(i) Enantiomers = Enantiomers are chiral molecules that are mirror images of one another.these molecules are non-superimposable on one another. This means that the molecules cannot be placed on top of one another and give the same molecule. Chiral molecules with one or more stereocenters can be enantiomers. It is sometimes difficult to determine whether or not two molecules are enantiomers. For introductory purposes, simple molecules will be used as examples. example is eszopiclone (Lunesta),

(ii) Diastereomers = Diastereomers contain chiral centers are non-superimposable but are NOT mirror images. There can be many more than 2 depending on the number of stereocenters.In the case of 2 chiral centers, 4 stereoisomers are possible.  Only the exact opposites will be enantiomers and they therefore have a mirror image that is not superimposable. The molecules with only one stereocenter that differs (parallel arrows) are diastereomers. example consider two compounds with a six-membered ring that have two substituents each, a chlorine atom and an ethyl group.

(iii) Meso Compound =Meso compounds are achiral compounds that has multiple chiral centers. It is superimposed on its mirror image and is optically inactive despite its stereocenters.pentane, butane, heptane, and even cyclobutane.

(iv)Archiral Molecule =A molecule is achiral if it is superimposable on its mirror image. Most achiral molecules do have a plane of symmetry or a center of symmetry. For example, two pieces of paper are achiral

(v) optical activity =Optical activity is the ability of a chiral molecule to rotate the plane of plane-polairsed light, measured using a polarimeter. A simple polarimeter consists of a light source, polarising lens, sample tube and analysing lens.For example, a 50:50 mixture of two enantiomers or a racemic mixture will not rotate plane polarised light and is optically inactive.