Chapter 2 Stereochemistry( 立体化 学） Stereochemistry refers to the 3-dimensional properties and reactions of molecules. It has its own language and terms that need to be learned in order to fully communicate and understand the concepts.
Definitions Stereoisomers （立体异构体 ） – compounds with the same connectivity, different arrangement in space Enantiomers （对映异构体） – stereoisomers that are non-superimposible mirror images; only properties that differ are direction (+ or -) of optical rotation Diastereomers （非对映异构体） – stereoisomers that are not mirror images; different compounds with different physical properties
More Definitions Asymmetric center – sp 3 carbon with 4 different groups attached Optical activity – the ability to rotate the plane of plane – polarized light Chiral compound （手性化合物） – a compound that is optically active (achiral compound will not rotate light) Polarimeter （旋光计） – device that measures the optical rotation of the chiral compound
Plane-Polarized Light （平面偏光）
Plane-Polarized Light through an Achiral Compound
Plane-Polarized Light through a Chiral Compound
Polarimeter Measures Optical Rotation
Specific Rotation （比旋光度）, [α] [α] = α / cl = observed rotation c = concentration in g/mL l = length of tube in dm Dextrorotary （右旋） designated as d or (+), clockwise rotation Levorotary （左旋） designated as l or (-), counter-clockwise rotation
Specific Rotations of some Common Organic Compounds Compound[ ]# * centers Penicillin V Sucrose Camphor （樟脑） MSG Cholesterol （胆固醇） Morphine
Chirality Center Carbon has four different groups attached
Enantiomers nonsuperimposible mirror images
Enantiomeric Excess （对映体过量百分 比） (Optical Purity) （光学纯度）
Biological Activity
SSRI Efficacy depends on Stereochemistry
Absolute Configuration （绝对购型）
Assign Priority to each Group on Asymmetric Center
Lactic Acid
C.I.P. Priorities （优先权）
Fischer Projections
Assigning Absolute Configuration to Fischer Projections
Rotation of the Projection 90 o Reverses Absolute Configuration
Diastereomers Stereoisomers That Are Not Mirror Images
Fischer Projections with 2 Chiral Centers
2 Chiral Centers 4 Stereoisomers
Identical, Enantiomers or Diastereomers?
Tartaric Acids （酒石酸）
Racemic Mixture （外消旋混合物）
Meso Compound （内消旋化合物） Internal Plane of Symmetry Optically Inactive
2,3,4-trichlorohexane How many stereoisomers?
n = 3; 2 n = 8
A Carbohydrate
Internal Planes of Symmetry
Asymmetric Centers on Rings 翻转
Allenes （丙二烯） can be Chiral
Mycomycin （菌霉素）, an antibiotic
Reactions that Generate Chirality Centers Hydrogenation, syn
Bromination Trans is formed exclusively No Meso is formed (cis)
Bromonium Ion is Opened Equally from Both Sides
trans alkene + anti addition = MESO
cis Alkene + anti addition = racemic mixture
Brominations Often Generate Asymmetric Centers
Asymmetric Center is Generated Racemic Mixture Formed
Asymmetric Induction
Preparation of (L)-Dopa for Treatment of Parkinson ’ s
Relevance of Stereochemistry
One-step synthesis
-(p-isobutylphenyl)propionic acid
Model of Thalidomide
How Sweet it is! Sucralose is 600 times sweeter and does not get metabolized.
Sildenafil (Viagra) and Caffeine
Radiosensitizer of Choice Until 2004