Isomers:Different compounds with same molecular formula Stereoisomers:isomers that have same molecular formula and connectivity but differ in the way the atoms are oriented in space - i.e. the difference between two stereoisomers lies only in the three dimensional arrangement of atoms. Stereochemistry:chemistry that studies the properties of stereo- isomers
Two types of stereoisomers: ◦ enantiomers two compounds that are nonsuperimposable mirror images of each other ◦ diastereomers Two stereoisomers that are not mirror images of each other Geometric isomers (cis-trans isomers) are one type of diastereomers.
The Light whose electric fields oscillate in single plane.
The ability of a compound to rotate the plane polarized light either clockwise or anti- clockwise. E.g. Tartaric Acid
Substances should be light sensitivity.They should have chiral carbonThey should rotate plane polarized light(PPL) in different ways.As a result, they should produce twodifferent configurations i.e. enantiomers
An optically active compound that rotates plane polarized light in a clockwise direction e.g. (+)Epinephrine
An optically active compound that rotatesplane polarized light in anti-clockwisedirection. E.g. (-) Epinephrine
A carbon which is bonded with four differentgroups.
Some molecules are chiral: Asymmetric (chiral) carbon
Organic compounds that contain a chiral Carbon usually have two non superimposable structures. These two structures are mirror images of each other.
Have identical molecular formula Have same physical properties Both rotate plane polarized light (PPL) but in opposite sense. One rotates PPL to clockwise and another to anti-clockwise.
Equimolar mixture of left- and right-handed enantiomers of a chiral molecule. Properties Optically inactive i.e. zero (0) rotation Sometimes have different properties of either pure enantiomers Different in solubility, melting and boiling points.Example: Ibuprofen
A compound with two identical chirality centerhaving no optical sensitivity because-They have two identical chiral partsOne part is optically active and another partis inactive.Optically active parts is neutralizes byinactive parts.As a result they have no light sensitivity
Racemic mixture Meso compoundMixture of two Equimolar One compound having twoenantiomers identical chiral parts.Individually light sensitive Though chiral C is present,but the mixture s neutral the compound is not light sensitiveComponents of the one compound, so twomixture can be separated. chiral parts can’t be separated.Mixture of d-lactic acid and Tartaric acidl-lactic acid
Stereoisomers are different compounds and often have different properties. Each stereoisomer must have a unique name. The Cahn-Ingold-Prelog convention is used to identify the configuration of each asymmetric carbon atom present in a stereoisomer. ◦ (R) and (S) configuration
The two enantiomers of alanine are: CO2H CO2H C C H H CH3 H3C NH2 H2N Natural alanine Unnatural alanine (S)-alanine (R)-alanine
Assign a numerical priority to each group bonded to the asymmetric carbon: ◦ group 1 = highest priority ◦ group 4 = lowest priority Rules for assigning priorities: ◦ Compare the first atom in each group (i.e. the atom directly bonded to the asymmetric carbon) Atoms with higher atomic numbers have higher priority
Cl 1 3 CH3 3 C 2 C H4 H3C OCH2CH3 NH2 H 1 F 2 4Example priorities:I > Br > Cl > S > F > O > N > 13C > 12C > 3H > 2H > 1H
In case of ties, use the next atoms along the chain as tiebreakers. 2 CH CH Br 2 2 C H4 3 CH3 2 CH CH(CH3)2 1 CH(CH3)2 > CH2CH2Br > CH3CH2
Y C Y C Y C Y C Treat double and triple bonds as if both YC C O atoms in the Y Y were duplicated or Y C bond C CO C triplicated: H Y C Y C C Y Y OHH C Y C Y C Y C Y C CH2OH C Y C Y C Y C Y C O 2 H C C O Y C Y C C Y2 O C H Y 1 C C OH C 1 OH 4 H CH2OH C4 H Y CH2OH 3 C Y3 Y C
Using a 3-D drawing or model, put the 4th priority group in back. Look at the molecule along the bond between the asymmetric carbon and the 4th priority group. Draw an arrow from the 1st priority group to the 2nd group to the 3rd group. ◦ Clockwise arrow (R) configuration ◦ Counterclockwise arrow (S) configuration
Theenantiomer with most remote OH from the CHO to the right is called D(+) enantiomer E.g. D(+) glyceraldehyde Theenantiomer with most remote OH from the CHO to the left is called L(-) enantiomer E.g. L(-) glyceraldehyde
Except for inorganic salts and a few low- molecular-weight organic substances, the molecules of living systems are chiral Although these molecules can exist as a number of stereoisomers, generally only one is produced and used in a given biological system amino acids, nucleosides, carbohydrates and phospholipids are chiral molecules
Bindingof drugs with enzymes depend on chirality