Symmetry The World of Organic Molecules. What is Symmetry?

SymmetryThe World of Organic Molecules

What is Symmetry?

Symmetry is likeness of shape or arrangement about a center.

Does this Design Have Symmetry?

Symmetry About a PlaneSymmetry About a Plane

Anything that contains an internal mirror Anything that contains an internal mirror plane is symmetric.plane is symmetric.

Anything that lacks an internal mirror plane Anything that lacks an internal mirror plane is asymmetric.is asymmetric.

ChiralityChirality

Asymmetric objects have an interesting Asymmetric objects have an interesting property called Chirality which means property called Chirality which means “handedness”.“handedness”.

Chiral objects can have two different forms, Chiral objects can have two different forms, a right-handed and left-handed form which a right-handed and left-handed form which are mirror images of each other but are are mirror images of each other but are not exactly alike.not exactly alike.

Examples of Chiral ObjectsExamples of Chiral Objects

Your Hands and FeetYour Hands and Feet

Gloves and ShoesGloves and Shoes

Golf ClubsGolf Clubs

Computer keyboardComputer keyboard

Are the Following Objects Are the Following Objects Chiral or Achiral?Chiral or Achiral?

Baseball BatBaseball Bat

RefrigeratorRefrigerator

CarCar

BicycleBicycle

Your FaceYour Face

ForkFork

NailNail

ScrewScrew

Chiral Molecules?Chiral Molecules?

A carbon atom with four different groups A carbon atom with four different groups bonded to it creates a stereocenter in the bonded to it creates a stereocenter in the molecule.molecule.

Most molecules which contain one or more Most molecules which contain one or more stereocenters lack an internal plane of stereocenters lack an internal plane of symmetry and are therefore chiral.symmetry and are therefore chiral.

EnantiomersEnantiomers

The right-handed and left-handed forms of a The right-handed and left-handed forms of a chiral molecule make up a pair of stereoisomers chiral molecule make up a pair of stereoisomers called enantiomers.called enantiomers.

Enantiomers are not identical, but they have the Enantiomers are not identical, but they have the same physical properties such as melting point same physical properties such as melting point boiling point, etc.boiling point, etc.

So why do we care about this subtle form of So why do we care about this subtle form of stereoisomerism?stereoisomerism?

Chirality in the Biological WorldChirality in the Biological World

When chiral organic compounds interact with When chiral organic compounds interact with living systems, the two enantiomers often living systems, the two enantiomers often interact very differently.interact very differently.

This is because living systems are chiral at This is because living systems are chiral at many different levels in many ways:many different levels in many ways:- our hands and feet are chiral (of course)- our hands and feet are chiral (of course)- our taste buds are chiral- our taste buds are chiral- our olfactory sensors are chiral- our olfactory sensors are chiral

- our enzymes are chiral- our enzymes are chiral

Carvone

O

CH3

CH3

H

CH3

H

O

H3C

Carvone

O

CH3

CH3

H

CH3

H

O

H3C

Left-handed Carvone

Smells like caraway

Right-handed Carvone

Smells like spearmint

Limonene

CH3

CH3

H

CH3

H

H3C

Limonene

CH3

CH3

H

CH3

H

H3C

Left-handed Limonene

Smells HarshTurpentine-like

Right-handed Limonene

Smells like fresh organges

Aspartame

H2N

N

O

O

O

H

H

O

OH

H

H2N

N

O

O

O

H

H H

O

OH

Aspartame

H2N

N

O

OH

O

H

H

O

OH

H

Left-handed Aspartame"Nutrasweet"160 times sweeter than sugar

H2N

N

O

OH

O

H

H H

O

OH

Right-handed AspartameNot at all sweetslightly bitter

Ibuprofen

H3C

O

OH

CH3

O

HOH H

Ibuprofen

H3C

O

OH

CH3

O

HO

Left-handed IbuprofenPowerful Pain Killer and Anti-inflamatory Drug

H H

Right-handed IbuprofenNo Drug Activity

Summary

• Molecules which lack symmetry are Chiral

• Chiral molecules have right-handed and left-handed forms

• Right-handed and left-handed molecules interact with living systems in very different ways.– Different smell– Different taste– Different drug effects