StructuralGeometricEnantiomer
Isomers
Isomers
Compounds that have the same molecular formula (same type and number of atoms) but different structure and different properties
3 types:Structural isomersGeometric isomersEnantiomers
Structural Isomer
SAME molecular formula but the atoms are connected differently
Structural isomers usually have different physical and chemical properties
Structural Isomer Example
Structural Isomer Example
Structural Isomer Example
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 yoursTry to rotate your bonds until your model looks
like they other groupsCan it be done without breaking apart bonds?
Geometric Isomer Example
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 belowHow 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 belowCan 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 think is necessary for a pair of molecules to be enantiomers? X
Enantiomer
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 symmetryMirror image is non-superimposable
Achiral Molecule
lacks chiral properties has a plane of symmetryMirror image is superimposable (rotate the
molecules to make them identical)
Practice: Identify the chiral carbons
Double bond to carbon = 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 mixture
Story 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 mixtureOne of the enantiomers is effective as an anti-
inflammatoryTakes 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.htmThe 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
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 NO
Are the substituent groups different? Is there a mirror image and a chiral carbon? YES NO YES NO
Steps to identifying isomers
Summary
Isomer Same Different Requirements
Structural
Geometric
Enantiomer
Summary
Isomer Same Different Requirements
StructuralMolecular
formulaConnectivity
Geometric
Enantiomer
Summary
Isomer Same Different Requirements
StructuralMolecular
formulaConnectivity
GeometricMolecular formula &
connectivity
Spatial arrangement
Double bond
Different substituent groups on each carbon
Enantiomer
Summary
Isomer Same Different Requirements
StructuralMolecular
formulaConnectivity
GeometricMolecular formula &
connectivity
Spatial arrangement
Double bond
Different substituent groups on each carbon
EnantiomerMolecular formula &
connectivity
Spatial arrangement
Chiral molecules
Mirror image
Summary
Isomer Structural Geometric Enantiomer
Same molecular formulaSame connection between atomsHas an inflexible bond with 2 different substituent groupsIs a mirror image with a chiral carbon
Summary
Isomer Structural Geometric Enantiomer
Same molecular formula
Same connection between atoms
Has an inflexible bond with 2 different substituent groups
Is a mirror image with a chiral carbon
Practice: Identify the chiral carbon
Practice: Identify the chiral carbon
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Practice: Determine the type of isomer
structural isomers
structural isomers
geometric isomers
Practice: Identify the chiral carbons
structural isomers
structural isomers
geometric isomers
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Practice: Identify the chiral carbons
Homework
Isomer WorksheetAnswer to HW question (next slide)
HW Question
Why is the ring form of glucose and galactose not structural isomers? Why are they geometric isomers? [2 marks]