260 likes | 560 Views
Stereochemistry. Stereochemistry: The study of the three-dimensional structure of molecules Structural (constitutional) isomers: same molecular formula but different bonding sequence Stereoisomers: same molecular formula, same bonding sequence, different spatial orientation. (S)- ketamine.
E N D
Stereochemistry: • The study of the three-dimensional structure of molecules • Structural (constitutional) isomers: • same molecular formula but different bonding sequence • Stereoisomers: • same molecular formula, same bonding sequence, different spatial orientation
(S)-ketamine • The properties of many drugs depends on their stereochemistry: (R)-ketamine anesthetic hallucinogen
Optical Isomerism • Optical Activity • The property of the substance to rotate the plane of • the plane-polarized light is known as optical activity. • Dextro-rotatory (+) • Laevorotatory (- ) Necessary condition: Molecule should be dissymmetric. Example: Biphenyl 2, 2’ – disulphonic acid
Enantiomers Enantiomers are defined as the isomers where molecular Structures are mirror images of each other and which rotate the plane of the polarized light equally but in opposite directions. Chirality is the necessary and sufficient condition for the existence of enantiomers. - Properties of enantiomers
Chiral vs. Achiral Example: Identify the following molecules as chiral or achiral.
DiastereomersPair of molecules with two or more different chiral carbon atoms which are neither identical nor non-superimposable mirror images of each other.
Meso Compound A compound with two or more asymmetric carbon atoms but also having a plane of symmetry (a mirror plane) is called the Meso compound.
Assign Priority to each Group on Asymmetric Center Example priorities: I > Br > Cl > S > F > O > N > 13C > 12C > 3H > 2H > 1H
(R) and (S) Nomenclature • The two enantiomers of alanine are: Natural alanine Unnatural alanine (S)-alanine (R)-alanine
(R) and (S) Nomenclature 2 4 3 1 CH(CH3)2 > CH2CH2Br > CH3CH2
Reactions that Generate Chirality Centers Hydrogenation, syn
BrominationTrans is formed exclusivelyNo Meso is formed (cis)