Announcements

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Announcements Agenda (03/05/07)

• Pick up Movie Quiz
• Exam next Wednesday!
• Covers Ch 7, 8, 10-12
• Will post a practice exam by Wed
• Grade sheets will be given on Wed (sorry ?)
• Come visit Bob!!!
• Today
• Cis-trans isomers (11.2)
• Reactivity of unsaturated compounds (11.3)
• Aromatic Compounds (11.5)

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Last Time Functional Groups (Know these!!!)
These are some of the most important biological
functional groups!
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Last Time Saturated vs. Unsaturated Hydrocarbons
Unsaturated hydrocarbons

• have fewer H atoms attached to the C chain than
  alkanes
• are alkenes with double bonds
• If one CC bond, CnH2n
• Monounsaturated 1 D.B.
• are alkynes with triple bonds
• If one CC bond, CnH2n-2

Naming Know ene means alkene group
present Know yne means alkyne group present
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Last Time Unsaturated Fatty Acids

• Fatty acids in vegetable oils are omega-6 acids
  (the first double bond occurs at carbon 6
  counting from the methyl group)
• A common omega-6 acid is linoleic acid
• CH3CH2CH2CH2CH2CHCHCH2CHCH(CH2)7COOH
• 6
• linoleic acid, a fatty acid

an alkene group
a carboxylic acid group
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Last Time Unsaturated compounds are oxidized
relative to saturated compounds

• Oxidation of organic compounds means
• Replacement of hydrogen atom with a more
  electronegative atom (oxygen or nitrogen)
• OR
• Loss of H atoms replacement with a double bond

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Bond Angles in Alkenes Alkynes

• According to VSEPR theory
• the 3 groups bonded to C atoms in a double bond
  are at 120 angles.
• alkenes are flat because the atoms in a double
  bond all lie in the same plane.
• the 2 groups bonded to each carbon in a triple
  bond are at 180 angles.

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How do you make a double bond?

• The 1st bond is made by orbitals overlapping
• between atoms, and is called a sigma (s)
  bond.
• The 2nd bond is made by sideways p orbitals
• (not directly between the atoms) and is
  called a
• pi (p) bond.
• This is why a single bond can rotate. But the p
• bond part of a double bond cant rotate
  youd
• have to break it.

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Steroisomers Cis-Trans Isomers

• In an alkene, the double bond
• is rigid, i.e. NO ROTATION around the double
  bond!
• holds attached groups in fixed positions.
• makes cis/trans isomers possible.
• Important in nature such as in pheromones
• CH3 CH3 CH3
• CH CH CH CH
• cis trans CH3
• (similar groups on same side) (similar groups
  on opp. sides)

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Cis-Trans Isomerism

• Alkenes cannot have cis-trans isomers if a C atom
  in the double bond is attached to identical
  groups.
• Identical Identical
• 2-bromopropene
  1,1-dibromoethene
• (not cis or trans)
  (not cis or trans)

H
H
Br
H
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Cis-Trans Isomerization of Retinal
Present in Rhodopsin
From Lehninger Principles of Biochemistry 3rd ed.
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These guys are

• The exact same compound
• Stereoisomers (cis/trans)
• Constitutional (structural) isomers
• Different compounds that arent isomers

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These guys are

• The exact same compound
• Stereoisomers (cis/trans)
• Constitutional (structural) isomers
• Different compounds that arent isomers

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These guys are

• The exact same compound
• Stereoisomers (cis/trans)
• Constitutional (structural) isomers
• Different compounds that arent isomers

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Reactions of Alkenes

• 11.3
• Addition Reactions

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Addition Reactions

• The double/triple bond can be broken
• alkenes alkynes are very reactive.
• In addition reactions, reactants are added to the
  carbon atoms in the double or triple bond.

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Hydrogenation

• H2 adds to the C atoms of a double/triple bond.
• A catalyst (e.g. Pt or Ni) is used to speed up
  the reaction.

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Hydrogenation of Oils

• Adding H2 to double
• bonds in vegetable
• oils produces
• compounds with higher melting points.
• solids at room temperature such as margarine,
• soft margarine,
• and shortening.

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Trans Fats

• In vegetable oils, the unsaturated fats usually
  contain cis double bonds.
• During hydrogenation, some cis double bonds are
  converted to trans double bonds (more stable),
  which causes a change in the fatty acid
  structure.
• If a label states partially or fully
  hydrogenated, the fats contain trans fatty
  acids.

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Trans Fats So What?
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• 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 Reaction

• an acid H catalyst is required.
• water (HOH) adds to a double bond.
• an H atom bonds to one C in the double bond.
• an OH bonds to the other C.
• 
  H OH
• 
  H
• CH3-CHCH-CH3 H-OH CH3-CH-CH-CH3

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Hydration

• When hydration occurs with a double bond that has
  an
• unequal number of H atoms,
• the H atom bonds to the C in the double bond with
  the more H.
• the OH bonds to the C in the double bond with the
  fewer H atoms.
• OH H
• H
  
• CH3-CHCH2 H-OH CH3-CH-CH2

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Learning Check

• Write the addition product for each of the
  following
• 
  H
• 1. CH3-CH2-CHCH-CH2-CH3 HOH
• CH3
• H
• 2. CH3-CCH-CH2-CH3 HOH
• 3. CH3-CHCH-CH3 H2
• 4. HOH

Pt
H
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Solution

• H OH
• 1. CH3-CH2-CH-CH-CH2-CH3
• CH3
• 2. CH3-C-CH-CH2-CH3 3.
  CH3-CH2-CH2-CH3
• OH H
• OH
• 4.
• H

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One Last Thing about HydrationHydration is
also reversible the equilibrium amounts of
alkene compared to alcohol depend on how much
water is around.
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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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Spring Breakers Why too much UV is bad A
Reaction of Double Bonds!
DNA damage by UV radiation induces dimerization
of DNA bases (particularly T-T)
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Conjugated bonds
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• If you have alternating double single bonds,
• you get extended, conjugated pi bonds.
• what looks like a single bond in between two
  double bonds, is actually sort of a double bond
  itself.
• multiple pairs of electrons can spread out all
  the way through the aligned parallel orbitals -gt
  molecules like this!

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Why is blood red?

• Delocalization of course!

• Its the HEME in hemoglobin!!!

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Aromatic Compounds Special Conjugation

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

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Benzene 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 Health

• Vanillin Aspirin
• Ibuprofen
  Acetaminophen

Aromatics can be bad too ? Many are carcinogens!
Can interact with DNA.
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Aromatic rings can include N atoms, too.
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• They can be 5 or 6 membered rings (and gt), fused
  rings, etc.

Pyridine
Thymine
Adenine
Phenylalanine