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  • 1. IsomersStructural, Geometric, Enantiomer
  • 2. Isomers Compounds that have the same molecular formula but difference structure and different properties 3 types:  Structural isomers  Geometric isomers  Enantiomers
  • 3. Structural Isomer same KIND and AMOUNT of atoms (molecular formula) but the atoms have different connectivity Structural isomers usually have different physical and chemical properties
  • 4. Structural Isomer
  • 5. Structural Isomer
  • 6. Structural Isomer
  • 7. Structural Isomer
  • 8. Structural Isomer How many different structures can you make from C5H12?
  • 9. Geometric Isomers SAME molecular formula and the SAME connectivity but different spatial arrangements Due to inflexibility of a bond, usually either:  double bonds (cis and trans formation)  bonds that can’t rotate (i.e. in a ring formation)
  • 10. Geometric Isomers
  • 11. Geometric Isomer Why is example 1 not a pair of geometric isomers? Hint: Look at example 2 & 3 and compare to example 1. What is the minimum requirement for a pair of molecules to be considered geometric isomers?
  • 12. Geometric Isomer Answer: Each carbon of the double bond must have two different substituent groups So if example 1 is not a pair of geometric isomers, what are they classified as?
  • 13. Geometric Isomer Another type of geometric isomer is found in ring structures and doesn’t involve double bonds Due to the inflexible nature of the bonds that make up the ring Note: The ring lies on a flat plane (e.g. your paper) and the OH groups are perpendicular to the plane (e.g. up and down)
  • 14. Enantiomer Molecules that are mirror images of each other Note: left and right hands are a pair of enantiomers (mirror images not identical) What other body parts that are enantiomers?
  • 15. EnantiomerActivity: Build these molecule pairs Compare them to determine whether they are enantiomers
  • 16. Enantiomer
  • 17. Enantiomer How are the lower pairs of molecules different from the upper pairs? What condition do you think is necessary for a pair of molecules to be enantiomers? X
  • 18. Enantiomer Requirement: Enantiomers can only occur when each of the four groups attached to the central carbon atom are all different. The central carbon is known as a chiral carbon and the molecule is chiral.
  • 19. Chiral Molecules Asymmetric carbon: carbon with 4 different groups bonded to it No plane of symmetry Mirror image is non-superimposable
  • 20. Achiral Molecule lacks chiral properties has a plane of symmetry
  • 21. Practice:Identify the chiral carbonsDouble bond tocarbon = achiral
  • 22. Application: Amino acids Amino acids are building blocks of proteins Some amino acids can exist as enantiomers because of their chiralty Switching an enantiomer in a biological system can have detrimental effects
  • 23. Application: Enzymes Enzymes are always chiral. Their binding sites are in a specific orientation that fits only one form of an enantiomer. Binding sites won’t fit if the wrong enantiomer is present.
  • 24. Racemic mixture A mixture that contains equal quantities of both enantiomers Enantiomers can interconvert in vivo
  • 25. Racemic mixtureStory of thalidomide (1960’s) A racemic drug given to pregnant women to combat morning sickness One of the enantiomers caused birth defects (teratogen) and death http://www.thalidomide.ca/the-canadian-tragedy/
  • 26. Racemic mixtureWhat’s in Advil (ibuprofen)? Production results in a racemic mixture One of the enantiomers is effective as an anti-inflammatory Takes about 30 minutes for the inactive enantiomer to be converted http://www.brookscole.com/chemistry_d/templates/student_resources/0534389996_mcmurry/CHEM_A_WORK/chapter9.htm The World of Chemistry, 4 ed. 2007. Thomson Brooks/Cole. Joesten, Castellion, & Hogg.
  • 27. Steps to identifying isomers Do the molecules have the same chemical formula?  If the formula is different, they are NOT isomers but completely different molecules Are the molecules identical?  If they are, they are NOT isomers. Are all the atoms connected in the same way to other atoms?  If not, they are STRUCTURAL isomers Look for an inflexible bond (double bond or ring) for geometric isomers Look for mirror images for enantiomers http://2.bp.blogspot.com/_K91FA3B4cpM/SJ_NUmBWWGI/AAAAAAAAACY/UzL8H8Q4oag/s400/ist2_1744503_frustration.jpg
  • 28. Summary Isomer Same Different RequirementsStructuralGeometricEnantiomer
  • 29. Summary Isomer Same Different Requirements MolecularStructural Connectivity formulaGeometricEnantiomer
  • 30. Summary Isomer Same Different Requirements MolecularStructural Connectivity formula Molecular Double bond SpatialGeometric formula & Different substituent arrangement connectivity groups on each carbonEnantiomer
  • 31. Summary Isomer Same Different Requirements MolecularStructural Connectivity formula Molecular Double bond SpatialGeometric formula & Different substituent arrangement connectivity groups on each carbon Molecular Spatial Chiral moleculesEnantiomer formula & arrangement Mirror image connectivity
  • 32. Practice:Identify the chiral carbon
  • 33. Practice:Identify the chiral carbon * * * * * *
  • 34. Practice:Identify the chiral carbons structural isomers structural isomers geometric isomers
  • 35. Practice:Identify the chiral carbons structural isomers * * ** * * * * * * structural isomers geometric isomers * * * *