By: Mdm Rohazita Bahari ERT 102 Organic Chemistry 2017 2018 STEREOCHEMISTRY By: Mdm Rohazita Bahari ERT 102 Organic Chemistry 2017 2018

ISOMERS Isomers – Compound with the same molecular formula but different structures Constitutional Isomer – differ in the way their atoms are connected. Stereoisomer(Configurational isomer)- differ in the way their atom are arranged in space Devided by 2 types :Cis-trans isomers + isomers that contain asymmetric centers or known as chirality center.

ISOMERS

CONSTITUTIONAL ISOMERS Differ in the way their atoms are connected Example: C2H6O C4H9Cl

CONFIGURATIONAL ISOMER Cis-Trans Isomers Cis–trans isomers (also called geometric isomers) result from restricted rotation. Restricted rotation can be caused either by a double bond or by a cyclic structure. Cis isomer has the substituent on the same side of the double bond Trans isomer has the substituent on opposite sides of the double bond.

Cis-Trans Isomers(Example) Cis- isomer Trans- isomer

CONFIGURATIONAL ISOMER An Asymmetric Center Also known as a chirality center. An atom bonded to four different atoms or groups.

Chiral vs achiral CHIRAL ACHIRAL Nonsuperimposable mirror image. Its mirror image is not the same as itself. ACHIRAL Superimposable mirror image. It looks the same in the mirror

Enantiomers YELLOW GREEN BLUE

Drawing Enantiomers Perspective formula Solid lines – bonds in the plane of the paper Solid wedge- coming out of the paper toward you Hatched wedge - going back into space behind the paper The solid wedge and hatched wedge must be adjacent to one another.

Drawing Enantiomers Fischer projection Horizontal line – The bonds project out of the plane toward the viewer Vertical line- The bonds extend back from the plane away from viewer The carbon chain usually drawn vertically

The higher the atomic no. the higher the priority Naming Enantiomers The R,S system of nomenclature 1.Rank the groups (atoms) bonded to the asymmetric center in order to priority The higher the atomic no. the higher the priority

Naming Enantiomers The R,S system of nomenclature 2.Orient the molecules Lowest priority (4) directed away from you. 3.Draw imaginary arrow from the group of highest priority to the next highest priority If the arrow point clockwise (R-Configuration) Counterclockwise (S-Configuration)

Naming from the Perspective Formula 1. Rank the groups bonded to the asymmetric center with the lowest priority group in the back.

2. If the group (or atom) with the lowest priority bonded by a hatched wedge; Clockwise-R;Anticlockwise-S 3. If the group (or atom) with the lowest priority IS NOT bonded by a hatched wedge; then switch two groups so group 4 is bonded by a hatched wedge

Configuration from the Fischer Projection 1. Consider the 3-dimensional equivalent to the Fischer Projection. 2. Rank the groups (or atoms) that are bonded to the asymmetric center and then draw an arrow from the highest priority (1) to the next highest priority (2).

3. If the lowest priority is on a vertical bond; clockwise (R-Configuration),Counterclockwise (S-Configuration) 4. If the lowest priority is on a horizontal bond, the configuration is opposite to the direction of the arrow.

ISOMERS WITH MORE THAN ONE ASYMMETRIC CENTER Max no stereoisomer = 2n n= no. of asymmetric center

Diastereoisomers Stereoisomers (1) and (2) Stereoisomers (3) and (4) Stereoisomers (1) and (3),(1) and (4),(2) and (3), (2) and (4) ENANTIOMERS DIASTEREOISOMERS Diastereoisomers are stereoisomers that are not enantiomers

Identification of Asymmetric Carbons in Cyclic Compounds

Meso compounds are achiral molecules with asymmetric centers Have two or more asymmetric centers and an internal plane of symmetry (-plane) Meso compounds are achiral molecules with asymmetric centers

If a compound with two asymmetric centers has the same four groups bonded to each of the centers, one of its stereoisomers will be a meso compound

THE END THANK YOU