Structural, Geometric, Enantiomer

Isomers

Isomers

Compounds that have the same molecular formula but difference structure and different properties

3 types:

Structural isomers

Geometric isomers

Enantiomers

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

Structural Isomer

Structural Isomer

Structural Isomer

Structural Isomer

Structural Isomer

How many different structures can you make from C5H12?

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 Isomers

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

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)

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?

Enantiomer

Activity: Build these molecule

pairs Compare them to

determine whether they are enantiomers

Enantiomer

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

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

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 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 enantiomershttp://2.bp.blogspot.com/_K91FA3B4cpM/SJ_NUmBWWGI/AAAAAAAAACY/UzL8H8Q4oag/s400/ist2_1744503_frustration.jpg

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 bondDifferent substituent

groups on each carbon

Enantiomer

Summary

Isomer Same Different Requirements

StructuralMolecular

formulaConnectivity

GeometricMolecular formula &

connectivity

Spatial arrangement

Double bondDifferent substituent

groups on each carbon

EnantiomerMolecular formula &

connectivity

Spatial arrangement

Chiral moleculesMirror image

Practice: Identify the chiral carbon

Practice: Identify the chiral carbon

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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