PHC 211 PHC 211

StereochemistryStereochemistry

LEC. 6LEC. 6Tues, 1/11/1433 HTues, 1/11/1433 H

Dr. Maha Al-Mutairi

Lecture contents:

Significance of Chirality

More Than One Chiral Carbon

Meso Compounds

Revision

Lecture outcomes

By the end of this lecture, students able to:

Identify and calculate no. of isomers for compounds with more than one chiral carbon.

Recognize and state the characteristics of

meso compounds.

What is the Significance of

Chirality in the Biological

World?

Two chiral carbon:Two chiral carbon:

Each of these tow chiral carbons can be either (R) or (S).

The maximum number of optical isomers for a compound is 2n, where n is the number of chiral atoms.

More Than One Chiral CarbonMore Than One Chiral Carbon

Cont.More than one chiral carbon

Q: How many stereoisomers could exist for a compound has three different chiral three different chiral carbon?carbon?

))RR ( (And (S) system for a compound with two And (S) system for a compound with two chiral carbon atomschiral carbon atoms::

EXAMPLES:

A. 1,2-Dibromo-1-phenylpropane

B. 2,3,4-trihydroxybutanal (erthyrose)

Cont.More than one chiral carbon

Enantiomers and diastereomers:Enantiomers and diastereomers:

22--Bromo-3-chlorobutaneBromo-3-chlorobutane

Cont.More than one chiral carbon

Meso compounds

In the simplest case, they are compounds which have internal plan have internal plan of symmetryof symmetry.

EXAMPLE: Tartaric acid

COOH

H OH

COOH

H OH

Important properties of meso compounds with 2 chiral centers: 

1. They are optically inactive.

2. They must be (R,S) configuration.

3. They are diastereomers of the (R,R)

and (S,S) isomer.

Cont. Meso compounds