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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]