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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)

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Announcements agenda 03 05 07
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)


Last time functional groups know these
Last Time: Functional Groups (Know these!!!)

These are some of the most important biological functional groups!


Last time saturated vs unsaturated hydrocarbons
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 C=C bond, CnH2n

    • Monounsaturated = 1 D.B.

  • are alkynes with triple bonds

    • If one C≡C bond, CnH2n-2

Naming:

Know “ene” means alkene group present

Know “yne” means alkyne group present


Last time unsaturated fatty acids
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

    CH3CH2CH2CH2CH2CH=CHCH2CH=CH(CH2)7COOH

    6

    linoleic acid, a fatty acid

an alkene group

a carboxylic acid group


Last time unsaturated compounds are oxidized relative to saturated compounds
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


Bond angles in alkenes alkynes
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.


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.


Steroisomers cis trans isomers
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

    cistransCH3

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


Cis trans isomerism
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-bromopropene1,1-dibromoethene

    (not cis or trans) (not cis or trans)

H

H

Br

H


Cis-Trans Isomerization of Retinal

Present in Rhodopsin

From Lehninger Principles of Biochemistry 3rd ed.


These guys are
These guys are…

  • The exact same compound

  • Stereoisomers (cis/trans)

  • Constitutional (structural) isomers

  • Different compounds that aren’t isomers


These guys are1
These guys are…

  • The exact same compound

  • Stereoisomers (cis/trans)

  • Constitutional (structural) isomers

  • Different compounds that aren’t isomers


These guys are2
These guys are…

  • The exact same compound

  • Stereoisomers (cis/trans)

  • Constitutional (structural) isomers

  • Different compounds that aren’t isomers


Reactions of alkenes
Reactions of Alkenes

11.3

Addition Reactions


Addition reactions
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.


Hydrogenation
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.


Hydrogenation of oils
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.


Trans fats
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.


Trans fats so what

0

Trans 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


Hydration another addition reaction
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.

    HOH

    H+│ │

    CH3─CH=CH─CH3 + H─OH CH3─CH─CH─CH3


Hydration
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.

    OHH

    H+│ │

    CH3─CH=CH2 + H─OHCH3─CH─CH2


Learning check
Learning Check

Write the addition product for each of the following:

H+

1. CH3─CH2─CH=CH─CH2─CH3 + HOH

CH3

│ H+

2. CH3─C=CH─CH2─CH3 + HOH

3. CH3─CH=CH─CH3 + H2

4. + HOH

Pt

H+


Solution
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


0

One Last Thing about Hydration…Hydration is also reversible – the equilibrium amounts of alkene compared to alcohol depend on how much water is around.

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).


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)


Conjugated bonds

0 Double Bonds!

Conjugated bonds

  • 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 -> molecules like this!


Why is blood red
Why is blood red? Double Bonds!

  • Delocalization of course!

  • It’s the HEME in hemoglobin!!!


Aromatic compounds special conjugation
Aromatic Compounds Double Bonds!“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.


Benzene and aromaticity
Benzene and Aromaticity Double Bonds!

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


Occurrences in nature health
Occurrences in Nature & Health Double Bonds!

VanillinAspirin

IbuprofenAcetaminophen

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


Aromatic rings can include n atoms too

0 Double Bonds!

Aromatic rings can include N atoms, too.

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

Pyridine

Thymine

Adenine

Phenylalanine


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