Isomers Compounds that have the same molecular formula (same type and number of atoms) but different structure and different properties 3 types: Structural isomers Geometric isomers Enantiomers
Structural Isomer SAME molecular formula but the atoms are connected differently Structural isomers usually have different physical and chemical properties
Structural Isomer How many different structures can you make from C5H12?
Geometric Isomer Activity 1 Build a 2-pentene (C5H10) Find another group’s model that looks different from yours Try to rotate your bonds until your model looks like they other groups Can it be done without breaking apart bonds?
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)
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?
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?
Geometric Isomer Activity 2 Build these molecules: The ring lies on a flat plane (e.g. your paper) OH groups are perpendicular to the plane Compare the molecules. What is different between them? Can you rotate the bonds to make them identical?
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
Enantiomer Activity 1 Build the molecules below How is the structure of the molecules related? Can you rotate the bonds so that they are identical?
Enantiomer Molecules that are mirror images of each other Note: left and right hands are a pair of enantiomers (mirror images are not identical) What other body parts that are enantiomers?
Enantiomer Activity 2 Build the molecules below Can you rotate the bonds so that they are identical?
Enantiomer How are the lower pairs of molecules different from the upper pairs? What condition do you X think is necessary for a pair of molecules to be enantiomers?
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.
Chiral Molecules Asymmetric carbon: carbon with 4 different groups bonded to it No plane of symmetry Mirror image is non-superimposable
Achiral Molecule lacks chiral properties has a plane of symmetry Mirror image is superimposable (rotate the molecules to make them identical)
Practice: Identify the chiral carbonsDouble bond tocarbon = achiral
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
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.
Racemic mixture A mixture that contains equal quantities of both enantiomers Enantiomers can interconvert in vivo
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/
Racemic mixture What’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.
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
Steps to identifying isomers Molecules Do the molecules have the same molecular formula? YES NO: Are all the atoms connected in the same way? YES NO: Is there an inflexible bond? YES NOAre the substituent groups different? Is there a mirror image and a chiral carbon? YES NO YES NO
Summary Isomer Same Different RequirementsStructuralGeometricEnantiomer
Summary Isomer Same Different Requirements MolecularStructural Connectivity formulaGeometricEnantiomer
Summary Isomer Same Different Requirements MolecularStructural Connectivity formula Molecular Double bond SpatialGeometric formula & Different substituent arrangement connectivity groups on each carbonEnantiomer
Summary Isomer Same Different Requirements MolecularStructural Connectivity formula Molecular Double bond SpatialGeometric formula & Different substituent arrangement connectivity groups on each carbon Molecular Chiral molecules SpatialEnantiomer formula & arrangement Mirror image connectivity
SummaryIsomer Structural Geometric EnantiomerSame molecularformulaSame connectionbetween atomsHas an inflexiblebond with 2 differentsubstituent groupsIs a mirror imagewith a chiral carbon
SummaryIsomer Structural Geometric EnantiomerSame molecular formulaSame connection between atomsHas an inflexiblebond with 2 different substituent groupsIs a mirror image with a chiral carbon