CHEM 109A Organic Chemistry

Transcription

1 CEM 09A Organic Chemistry Chapter Isomers The arrangement of atoms in space MIDTERM Wednesday Feb. Chapter Sections.8.6 melting, boiling points, conformations acyclic (ethane, butane, etc.) and cyclic (cyclohexane) Chapter stereochemistry, all Chapter 5 Sections Alkenes: (formulas, nomenclature, structure), electrophiles and nucleophiles, curved arrows

2 ow to Draw Enantiomers Perspective formulas Skeletal structures Fischer projections R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures -butanol recognize there is a hydrogen pointing away a good position

3 R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures -butanol recognize there is a hydrogen pointing away a good position rank groups/substituents... from highest to lowest priority R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures -butanol (R)--butanol recognize there is a hydrogen pointing away a good position rank groups/substituents... from highest to lowest priority connect to to back to : clockwise R, counterclockwise S

4 R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures 80 o,-dichlorobutane recognize there is a hydrogen pointing toward the viewer rank groups/substituents... from highest to lowest priority R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures 80 o,-dichlorobutane recognize there is a hydrogen pointing toward the viewer rank groups/substituents... from highest to lowest priority OPTION: rotate 80 as shown to place lowest ranking pointing away

5 R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures 80 o,-dichlorobutane (S)-,-dichlorobutane recognize there is a hydrogen pointing toward the viewer rank groups/substituents... from highest to lowest priority OPTION: rotate 80 as shown to place lowest ranking pointing away connect to to back to : clockwise R, counterclockwise S name compound, placing the R or S in front in ( ) R and S configuration. Assigning Configuration and Naming Enantiomers Skeletal structures,-dichlorobutane (S)-,-dichlorobutane recognize there is a hydrogen pointing toward the viewer rank groups/substituents... from highest to lowest priority OPTION (easier?): keep going with assigning, but remember to switch: connect to to back to : clockwise R S, counterclockwise S R 5

6 Enantiomers O O N N O O (-)-morphine binds to opioid receptors in the brain (+)-morphine does not binds to opioid receptors in the brain assign the configuration of all stereocenters Compounds with Two Asymmetric Centers maximum # of stereoisomers = n (n = # of asymmetric centers) stereoisomers of -chloro--butanol and are. and are. 6

7 Diastereomers: stereoisomers that are not stereoisomers of -chloro--butanol Diastereomers are stereoisomers that are not. and are diastereomers. and are diastereomers. and are diastereomers. and are diastereomers. Diastereomers have different physical and chemical properties. Perspective Formulas of the Four Stereoisomers 7

8 Two Asymmetric Centers, Four Stereoisomers The cis stereoisomers are a pair of. The trans stereoisomers are a pair of. Identifying an Asymmetric Center An asymmetric center is attached to four different groups. two asymmetric centers, four stereoisomers 8

9 No Asymmetric Centers There are only two stereoisomers: cis and trans. No Asymmetric Centers There are only two stereoisomers: cis and trans. 9

10 Two Asymmetric Centers: Meso Compound When substituents at the centers are the same one diastereomer is not chiral It is called a meso compound identical identical Two Asymmetric Centers: Meso Compound When substituents at the centers are the same one diastereomer is not chiral identical 80 o identical plane of symmetry not chiral identical 0

11 A Meso Compound as a Superimposable Mirror Image Meso compounds are optically inactive even though they have asymmetric centers. A Meso Compound as a Plane of Symmetry

12 A Meso Compound meso two asymmetric centers, the same four groups bonded to each - three stereoisomers: a meso compound and a pair of. A Meso Compound: still has asymmetric centers let s assign their configuration and provide full systematic names meso

13 /6/8 A Meso Compound For cyclic compounds with the same substituents bonded to two asymmetric centers, cis = a meso compound and trans = a pair of. Naming Stereoisomers

14 Naming Stereoisomers Naming Stereoisomers

15 Physical Properties of Stereoisomers Nitrogen and Phosphorus Can Be Asymmetric Centers 5

16 Amine Inversion If one of the four groups attached to N is a lone pair, the cannot be separated, because they interconvert as a result of amine inversion. A Receptor is a Protein Proteins are Chiral Molecules Because a receptor is chiral, it binds one enantiomer. A right-handed glove fits only a right hand. 6

17 A Receptor Binds One Enantiomer Each enantiomer binds to a different receptor in the nose. Physiological Properties of Enantiomers Enantiomers can have very different physiological properties. 7

18 Separating Enantiomers separating by hand separating by chromatography 8