Stereochemistry

Overview

1. Chirality.
2. Chan-Ingold-Prelog
3. Optical Activity.
4. Enantiomeric Excess
5. Enantiomers and Diastereomers.

1. Chirality

Chiral = have 1 Enantiomer (a non-superimposible mirror image)

2. Chan-Ingold-Prelog

  1. Assign Priorities based on highest atomic number.
  2. Rotate the mocleule, so that 4th priority is on the dash(beghind the page).
  3. See if sequnce 1,2,3 is:
    Clockwise = R
    Counter Clockwise = S


3. Optical Activity.

Enantiomers exhibit identical physical properties, however they rorate polorized light diferentley.

D = +
L = -



Specific Rotation [α] = α / c * L

α - observed rotation
c - concentration (g/ml)
L - pathlength

Beware:

Temperature and Wavelenght can affect [α], but they are not included in the formula, instead they are reported.
In the example below T = 20C and; D stands for D line of sodium (589nm)


Beware:

L and D does NOT correlate with R and S. In the example below, the same compound changes light rotation depending on the T.

4. Enantiomeric Excess

EE - is a mesurment of the purity of the compound.

% ee = |experimental α| / |standard α| * 100%

How to calculate it?


experimental/observed α = -53
standard/pure α = -45

1.
%ee = 45/53 * 100% = 85%

2.
85% - pure
15% - racemic mixture (7.5% of each D and L)

3.
85% + 7.5% = 92.5% of desired product.
7.5% of contaminant enantiomere.

5. Enantiomers and Diastereomers.