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AnnouncementsAnnouncements & Agenda& Agenda (03/05/07)(03/05/07)Pick up Movie QuizPick up Movie QuizExam next Wednesday!Exam next Wednesday! Covers Ch 7, 8, 10-12Covers Ch 7, 8, 10-12 Will post a practice exam by WedWill post a practice exam by Wed Grade sheets will be given on Wed (sorry Grade sheets will be given on Wed (sorry )) Come visit Bob!!!Come visit Bob!!!

TodayToday Cis-trans isomers (11.2)Cis-trans isomers (11.2) Reactivity of unsaturated compounds (11.3)Reactivity of unsaturated compounds (11.3) Aromatic Compounds (11.5)Aromatic Compounds (11.5)

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Last Time: Functional Groups (Know these!!!)Last Time: Functional Groups (Know these!!!)

These are some of the most important biological These are some of the most important biological functional groups!functional groups!

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• have fewer H atoms have fewer H atoms attached to the C chain attached to the C chain than alkanesthan alkanes

• are are alkenesalkenes with double with double bonds bonds

• If one C=C bond, CIf one C=C bond, CnnHH2n2n

• Monounsaturated = 1 D.B.Monounsaturated = 1 D.B.• are are alkynesalkynes with triple with triple

bonds bonds • If one CIf one C≡≡CC bond, bond, CCnnHH2n-22n-2

Last Time: Last Time: Saturated vs. Unsaturated HydrocarbonsSaturated vs. Unsaturated Hydrocarbons

Unsaturated hydrocarbonsUnsaturated hydrocarbons

Naming:Naming:

Know “ene” means Know “ene” means alkene group presentalkene group present

Know “yne” means Know “yne” means alkyne group presentalkyne group present

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Last Time: Unsaturated Fatty AcidsLast Time: Unsaturated Fatty Acids

Fatty acids in vegetable oils are omega-6 acids (the Fatty acids in vegetable oils are omega-6 acids (the first double bond occurs at carbon 6 counting from first double bond occurs at carbon 6 counting from the methyl group)the methyl group)

A common omega-6 acid is linoleic acidA common omega-6 acid is linoleic acid

CHCH33CHCH22CHCH22CHCH22CHCH22CH=CHCHCH=CHCH22CH=CH(CHCH=CH(CH22))77COOHCOOH

66linoleic acid, a fatty acid linoleic acid, a fatty acid

an alkene group

a carboxylic acid group

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Last Time: Unsaturated compounds are Last Time: Unsaturated compounds are oxidizedoxidized relative to saturated compounds relative to saturated compounds

Oxidation of organic compounds means:Oxidation of organic compounds means:

Replacement of hydrogen atom with a more Replacement of hydrogen atom with a more electronegative atom (oxygen or nitrogen)electronegative atom (oxygen or nitrogen)

OROR

Loss of H atoms & replacement with a double Loss of H atoms & replacement with a double bondbond

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Bond Angles in Alkenes & AlkynesBond Angles in Alkenes & Alkynes

According to VSEPR theory: According to VSEPR theory: • the 3 groups bonded to C the 3 groups bonded to C

atoms in a double bond are atoms in a double bond are at 120at 120° ° angles.angles.

• alkenes are flat because thealkenes are flat because the atoms in a double bondatoms in a double bond all lie all lie in the same plane.in the same plane.

• the 2 groups bonded to each the 2 groups bonded to each carbon in a triple bond are at carbon in a triple bond are at 180° angles.180° angles.

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How do you make a double bond?How do you make a double bond? The 1st bond is made by “orbitals” overlapping

between atoms, and is called a “sigma” (σ) bond.

The 2nd bond is made by sideways p orbitals (not directly between the atoms) and is called a “pi” (π) bond.

This is why a single bond can rotate. But the π bond part of a double bond can’t rotate – you’d have to break it.

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Steroisomers: Steroisomers: CisCis--TransTrans Isomers IsomersIn an alkene, the double bond In an alkene, the double bond • is rigid, i.e. NO ROTATION around the double bond!is rigid, i.e. NO ROTATION around the double bond!• holds attached groups in fixed positions. holds attached groups in fixed positions. • makes cis/trans isomers possible.makes cis/trans isomers possible.• Important in nature – such as in pheromonesImportant in nature – such as in pheromones

CHCH33 CHCH33 CH CH33

CH = CHCH = CH CH = CHCH = CH

ciscis transtrans CHCH33

(similar groups on same side) (similar groups on opp. sides)(similar groups on same side) (similar groups on opp. sides)

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Cis-Trans IsomerismCis-Trans Isomerism• Alkenes cannot have cis-trans isomers if a C atom in Alkenes cannot have cis-trans isomers if a C atom in

the double bond is attached to the double bond is attached to identical groupsidentical groups..

IdenticalIdentical Identical Identical

2-bromopropene2-bromopropene 1,1-dibromoethene 1,1-dibromoethene (not cis or trans)(not cis or trans) (not cis or trans) (not cis or trans)

C C

H Br

H CH3

C C

H Br

BrH

H

H

H Br

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Cis-Trans Isomerization of RetinalCis-Trans Isomerization of Retinal

From Lehninger Principles of Biochemistry 3rd ed.From Lehninger Principles of Biochemistry 3rd ed.

Present in RhodopsinPresent in Rhodopsin

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These guys are…These guys are…

0%0%0%0%1.1. The exact same compoundThe exact same compound

2.2. Stereoisomers (cis/trans)Stereoisomers (cis/trans)3.3. Constitutional (structural) isomersConstitutional (structural) isomers4.4. Different compounds that aren’t isomersDifferent compounds that aren’t isomers

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These guys are…These guys are…

0%0%0%0%1.1. The exact same compoundThe exact same compound

2.2. Stereoisomers (cis/trans)Stereoisomers (cis/trans)3.3. Constitutional (structural) isomersConstitutional (structural) isomers4.4. Different compounds that aren’t isomersDifferent compounds that aren’t isomers

H3C C C C CH3

H

H

H

H

H

H

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These guys are…These guys are…H

H H

Cl H

H Cl

H

0%0%0%0%1.1. The exact same compoundThe exact same compound

2.2. Stereoisomers (cis/trans)Stereoisomers (cis/trans)3.3. Constitutional (structural) isomersConstitutional (structural) isomers4.4. Different compounds that aren’t isomersDifferent compounds that aren’t isomers

11 22 33 44 55

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Reactions of AlkenesReactions of Alkenes

11.3 11.3 Addition ReactionsAddition Reactions

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Addition ReactionsAddition Reactions

• The double/triple The double/triple bond can be broken bond can be broken

• alkenes & alkynes are alkenes & alkynes are very reactive.very reactive.

• In In additionaddition reactions, reactions, reactants are added reactants are added to the carbon atoms in to the carbon atoms in the double or triple the double or triple bond.bond.

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• HH22 adds to the C atoms of a double/triple bond. adds to the C atoms of a double/triple bond.• A catalyst (e.g. Pt or Ni) is used to speed up the A catalyst (e.g. Pt or Ni) is used to speed up the

reactionreaction..

HydrogenationHydrogenation

HC CH + 2H2

NiHC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +

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Adding HAdding H2 2 to doubleto doublebonds in vegetablebonds in vegetableoils produces:oils produces:• compounds with compounds with

higher melting points.higher melting points.• solids at room solids at room

temperature such as temperature such as margarine,margarine,

soft margarine,soft margarine, and shortening. and shortening.

Hydrogenation of OilsHydrogenation of Oils

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TransTrans Fats Fats

In vegetable oils, the unsaturated fats usually In vegetable oils, the unsaturated fats usually contain contain ciscis double bonds. double bonds.

• During hydrogenation, some During hydrogenation, some cis cis double bonds are double bonds are converted to converted to trans trans double bonds (more stable), double bonds (more stable), which causes a change in the fatty acid structure.which causes a change in the fatty acid structure.

• If a label states “partially” or “fully hydrogenated”, If a label states “partially” or “fully hydrogenated”, the fats contain the fats contain transtrans fatty acids. fatty acids.

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TransTrans Fats: So What? Fats: So What?

• In the US, estimate 2-4% of our total Calories is in the form of trans fatty acid.

• trans fatty acids behave like saturated fatty acids in the body.

• Several studies reported that trans fatty acids raise LDL-cholesterol. Some studies also report that trans fatty acid lower HDL-cholesterol

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Hydration: Another Addition ReactionHydration: Another Addition Reaction• an acid Han acid H++ catalyst is required. catalyst is required.• water (HOH) adds to a double bond.water (HOH) adds to a double bond.• an H atom bonds to one C in the double bond.an H atom bonds to one C in the double bond.• an OH bonds to the other C.an OH bonds to the other C. HH OHOH HH++ │ ││ │CHCH33─CH=CH─CH─CH=CH─CH33 + + HH──OH OH CHCH33─CH─CH─CH─CH─CH─CH33

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HydrationHydration

When hydration occurs with a double bond that has anWhen hydration occurs with a double bond that has anunequal number of H atomsunequal number of H atoms,,• the H atom bonds to the C in the double bond with the H atom bonds to the C in the double bond with

the more H.the more H.• the OH bonds to the C in the double bond with the the OH bonds to the C in the double bond with the

fewer H atoms.fewer H atoms. OHOH HH

HH++ │ ││ │CHCH33─CH=CH─CH=CH22 + + HH──OHOH CHCH33─CH─CH─CH─CH22

2222

Learning CheckLearning Check

Write the addition product for each of the following:Write the addition product for each of the following: HH++

1. CH1. CH33─CH─CH22─CH=CH─CH─CH=CH─CH22─CH─CH3 3 + HOH+ HOH

CHCH33

││ HH++

2. CH2. CH33─C=CH─CH─C=CH─CH22─CH─CH3 3 + HOH+ HOH

3. CH3. CH33──CHCH=CH=CH──CHCH33 + H + H22

4. + HOH4. + HOH

Pt

H+

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SolutionSolution

H OHH OH │ ││ │1. CH1. CH33─CH─CH22─CH─CH─CH─CH─CH─CH22─CH─CH3 3

CHCH33

││ 2. CH2. CH33─C─CH─CH─C─CH─CH22─CH─CH3 3 3. CH3. CH33──CHCH22-CH-CH22──CHCH33 │ ││ │ OH HOH H

OHOH4. 4. H H

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One Last Thing about Hydration…One Last Thing about Hydration…

Hydration is also reversible – the equilibrium amounts of Hydration is also reversible – the equilibrium amounts of alkene compared to alcohol depend on how much water is alkene compared to alcohol depend on how much water is aroundaround..

Lots of water – the reaction tends to use up as much water as it can, and most of the alkene forms alcohol.

If water is removed, water can be pulled off from alcohol to form the alkene. (concentrated acid).

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H2C CH2

H2C CH2

H2C CH2

CH2H2C

DNA damage by UV DNA damage by UV radiation: induces radiation: induces dimerization of DNA dimerization of DNA bases (particularly T-T)bases (particularly T-T)

Spring Breakers: Why too much UV is Spring Breakers: Why too much UV is bad… A Reaction of Double Bonds!bad… A Reaction of Double Bonds!

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Conjugated bondsConjugated bondsIf you have alternating double & single bonds, If you have alternating double & single bonds,

• you get “extended, conjugated” pi bonds. you get “extended, conjugated” pi bonds.

• what looks like a single bond in between two double what looks like a single bond in between two double bonds, is actually sort of a double bond itself. bonds, is actually sort of a double bond itself.

• multiple pairs of electrons can spread out all the way multiple pairs of electrons can spread out all the way through the aligned parallel orbitals -> molecules like this!through the aligned parallel orbitals -> molecules like this!

C CCC

H

H

H

H

H H

CC

CC

H

H

H

H

H

H

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Why is blood red?Why is blood red?Delocalization of course!Delocalization of course!

Fen+N

N N

NH3C

CH2 CH3

CH2

CH3H3C

OHOOHO

• It’s the HEME in hemoglobin!!!It’s the HEME in hemoglobin!!!

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One Important Example: BenzeneOne Important Example: Benzene (Know This One!) (Know This One!)• a ring of 6 C & 6 H atoms.a ring of 6 C & 6 H atoms.• a flat ring structure drawn with three double bonds. a flat ring structure drawn with three double bonds. • represented by 2 structures because electrons are represented by 2 structures because electrons are

shared among all the C atoms.shared among all the C atoms.

Aromatic Compounds Aromatic Compounds “Special Conjugation”“Special Conjugation”

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Benzene and AromaticityBenzene and Aromaticity

Aromatics are compounds that have conjugated pi bonds around a ring. Electrons love this, and aromatics are very stable.

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Occurrences in Nature & HealthOccurrences in Nature & Health

Vanillin Aspirin

Ibuprofen Acetaminophen

COH

O

O

C O CH3

CH

O

OCH3

OH

CH

CH3

COH

O

CH2

CH3

CHH3C

OH

NH

O

C CH3

Aromatics can be bad too Many are carcinogens! Can interact with DNA.

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Aromatic rings can include N atoms, too. Aromatic rings can include N atoms, too.

They can be 5 or 6 membered rings (and >), fused rings, They can be 5 or 6 membered rings (and >), fused rings, etc.etc.

N N

NNH

H2NHN

HN

O

O

N

H2N CH C

CH2

OH

O

Adenine ThyminePhenylalanine

Pyridine