Transcript Origins of Life - Yale University

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ORGANIC CHEMISTRY
2
Types of Organic Compounds
• Vast majority of over 20 million known
compounds are based on C: organic
compounds.
• Generally contain C and H + other elements
• Great variety of compounds
Isomerism
• Isomers have identical composition but
different structures
• Two forms of isomerism
– Constitutional (or structural)
– Stereoisomerism
• Constitutional
– Same empirical formula but different atomto-atom connections
• Stereoisomerism
– Same atom-to-atom connections but
different arrangement in space.
3
4
Structural Isomers
5
Stereoisomers: Geometric
Geometric isomers can occur when there is a
C=C double bond.
Cis-2-butene
Trans-2-butene
6
Stereoisomers: Optical
• Optical isomers are molecules with
non-superimposable mirror images.
• Such molecules are called CHIRAL
• Pairs of chiral molecules are
enantiomers.
• Chiral molecules in solution can rotate
the plane of plane polarized light.
Chiral Compounds and
Polarized Light
7
8
Stereoisomers Isomers
Chirality
generally occurs
when a C atom
has 4 different
groups attached.
Lactic acid
Stereoisomers Isomers
Lactic acid isomers are
nonsuperimposable
9
Chirality: Handedness in
Nature
These molecules are non-superimposable
mirror images.
10
Chirality: Handedness in
Nature
These amino acids are nonsuperimposable mirror images.
11
Stereoisomers in Nature
Right- and lefthanded seashells
The DNA here is
right-handed
12
13
Hydrocarbons
• Compounds of C and H
• Subgroups:
– Alkanes: C-C single bonds
– Alkenes: C=C double bonds
– Alkynes: carbon-carbon triple
bonds
– Aromatic: based on benzene
14
Hydrocarbons
• Alkanes have the general formula
CnH2n+2
• CH4 = methane
• C2H6 = ethane
• C3H8 = propane
• C4H10 = butane
• C5H12 = pentane
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16
Methane Hydrate, CH4(H2O)x
Methane
Hydrate,
CH4(H2O)x
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Methane Hydrate, CH4(H2O)x
Gas hydrates have been known for many years, and
combustion of a sample of methane hydrate is seen on
the front cover. Recently, however, vast deposits of
methane hydrate were discovered deep within
sediments on the floor of the world’s oceans. How these
deposits were formed is a mystery. But what is
important is their size. It is estimated that the global
methane hydrate deposits contain approximately 1013
tons of carbon, or about twice the combined amount in
all reserves of coal, oil, and conventional natural gas.
Now if scientists and engineers could only solve the
problem of extracting the methane conveniently and
safely!
CH 3CH2 CH 2CH2 CH 3
Pentane
Hydrocarbons
& Structural
Isomerism
19
CH3
CH 3CHCH 2CH3
2-Methylbutane
CH3
H3CCCH3
CH3
2,2-Dimethylpropane
Note names of isomers
Isomers of C5H12?
C5H12 has 3
structural isomers.
C6H14 has 5
C7H14 has 9
20
Hydrocarbons: Alkanes
Alkanes are colorless gases, liquids,
and solids
Generally unreactive (but undergo
combustion)
Not polar (or low polarity) and so are
not soluble in water.
21
Hydrocarbons: Cycloalkanes
All compounds are flexible.
Cyclohexane, C6H12, has interconverting
“chair” and “boat” forms.
Axial H ato m
H
H
4
H
H
Eq u ator ial H
atom
H
5
6
2
3
H
H
H
H
1
HH
Chair form
4
H
H
1
H
6
5
H
3
H
2
H
H
H
H
H
H
H
Boat form
H
H
H
H
5
4
H
3
HH
H
H
1
6
H
H
2
H
Chair form
H
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Alkenes: Compounds with
C=C Double Bonds
• How many isomers are possible for a
compound with the formula C4H8?
3 4
CH2CH3
H
1
C
H
1
C
2
C
H
H
1-butene
3
CH3
H
1
H3C
2
C
4
CH3
2
C
CH3
2-methylpropene
(isobutene)
H
4
CH3
H
3
C
2
C
H
cis-2-butene
1
H3 C
3
C
H
trans-2-butene
23
Alkenes—
Many Occur Naturally
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Reactions of Alkenes:
ADDITION REACTIONS
• Alkenes are unsaturated — more
bonds can form to the C atoms
• Molecules such as Br2, H2, HCl, HBr, and
H2O add to the double bond
H
C C + Br2
H
H
H
Br Br
H C C H
H H
1,2-dibromoethane
An Addition Reaction
Fat placed
in Br2 vapor
• The fat in bacon is partially unsaturated.
The fat adds Br2 to the C=C bonds.
• Fats can be “hydrogenated” with H2.
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An Addition Reaction
Fat placed
in Br2 vapor
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An Addition Reaction
• Fats can be “hydrogenated” with H2.
Peanut butter has partially hydrogenated
vegetable oil.
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Alkynes
• Alkynes have carbon-carbon triple bonds.
• C2H2: common name = acetylene
systematic name = ethyne
Preparation:
CaC2(s) + H2O(liq) -->
C2H2 (g) + Ca(OH)2(s)
∆Hfo(C2H2, g) = +226.7 kJ/mol
∆Hrxn for C2H2 + O2
= –1300 kJ/mol
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Aromatic Compounds
• Benzene, C6H6, in the
top 25 chemicals
produced in the U.S.
• Starting point for
hundreds of other
compounds.
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Resonance in Benzene
• C6H6 has two resonance structures with
alternating double bonds.
• The π electrons are delocalized over the ring.
H
C
H
C
C
H
HC C C H
H
H
H
C
C
H
C
C
H
CH
C
H
Resonance structures of benzene, C6 H6
H
C
HC
H
C
C
C
H
H
CH
Abbreviated representation
of resonance structures
Resonance in Benzene
• CC bond order is _______________
• C–C single bond = 154 pm
C=C bond = 134 pm
• CC bonds in benzene = 139 pm
π electrons delocalized
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Other Aromatic Hydrocarbons
Toluene
Naphthalene
Benzene Derivatives
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Aniline
Phenol
C6H5NH2
TNT
trinitrotoluene
C6H5OH
C6H4CH3(NO2)3
Naming Benzene Derivatives
Cl
1
6
2
3
5
4
34
Ortho to Cl
Meta to Cl
Para to Cl
1,4-dimethylbenzene
Common name: Para-xylene
Reactions of Aromatics
35
• Substitutions — not additions — are
typical.
CH3
+ CH3Cl
AlCl3
AlCl3 is a catalyst. Catalysts typically used in
aromatic substitutions.
+ HCl
36
Functional Groups
See CD-ROM Screens 11.5 & 11.6
37
Alcohols
• Characterized by –OH group
• Name: add –ol to name of hydrocarbon
Methanol
Butanol
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Structures of Alcohols
C3H5OH: how many structural isomers?
H
H
H
H
C
C
C
H
H
H
1-propanol
OH
H
H
OH H
C
C
C
H
H
H
H
2-propanol
Naming: Add -ol to name of 3-C hydrocarbon. Indicate
position of OH with number.
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Alcohol Properties
• Alcohols are a derivative of water
• Many alcohols dissolve in water
Methanol dissolves
in water.
Butanol is NOT soluble
in water.
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“Sterno”
• Alcohols burn in air
• A mixture of ethanol +
calcium acetate =
STERNO
GLYCOLS
Alcohols with Two OH Groups
Ethylene
glycol
Propylene
glycol
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42
Alcohol Reactions
Screen 11.6
Substitution
Elimination—the
reverse of addition
43
Sugars: Related to Alcohols
• Sugars are carbohydrates, compounds
with the formula Cx(H2O)y.
CHO
H OH
4
HO
HO
5
3
H
H
OH
2
H
3
H
OH
4
H
OH
5
H
HO
2
HO
1
OH
OH
a-D-glucose
H
1
CH2OH
H OH
4
HO
HO
5
HO
1
3
H
H
2
OH
H
b-D-glucose
Open chain form
What is the difference between a and b D-glucose?
OH
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Sucrose and Ribose
H OH
HO
HO
HO
H
OH
O
H
HO
H
O
H
CH2OH
a-D-Glucose
H
HO
H
O
OH
Fructose
H
OH
H
CH2 OH
OH
H
H
H
Ribose, a pentose in
the DNA backbone
45
Amines
Alcohols are derivatives of H2O (R–OH)
and amines are derivatives of NH3.
Methylamine
Dimethylamine
Trimethylamine
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Amines
Amines generally have terrible odors!
Cadaverine
Pyridine
Amines
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Amines, like NH3, are bases
2 C6H5NH2 (aq) + H2SO4(aq)
Aniline
2 C6H5NH3 +(aq) + SO42-(aq)
Anilinium ion
48
Amines
H+
Nicotine
Many natural
products
and drugs
(such as
nicotine and
cocaine) are
bases.
49
O
C
Aldehyde
Compounds with
Carbonyl Group
Carboxylic acid
Ketone
50
Structures of Aldehydes
Cinnamaldehyde
Odors from aldehydes and
ketones
Carboxylic Acids
Acetic acid
Acids are found in
many natural
substances: bread,
fruits, milk, wine
51
Benzoic acid
Carboxylic acid group
with acidic H+
All are WEAK acids
52
Carboxylic Acids
H
O
Formic acid,
HCO2H, gives
the sting to ants.
C
O
O
C
CH3
O
Aspirin, acetylsalicylic acid
53
Acids + Alcohols --> ESTERS
Esters have generally pleasant odors
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Acids + Alcohols --> ESTERS
O
O
CH 3COH + CH 3CH 2OH
Acetic acid
H+
CH 3COCH 2CH 3 + H 2O
Ethyl acetate
Ethanol
O
O
RC—O—H
+ R'—O—H
Carboxylic acid
Alcohol
H+
RC—O—R' + H 2O
Ester
One of the important reactions in nature!
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Acids + Alcohols --> ESTERS
3-methylbutanol
Acetic acid
O
H3C
C
CH3
O
CH2 CH2CHCH3
3-methylbutylacetate
Glycerol
Alcohol with 3 OH Groups
Combine this with long chain acids ------> ???
Fatty acids ---> fats and oils
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Fats and Oils
H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
What is the
functional group in a
fat or oil?
R = organic group
with NO C=C bonds
C12 = Lauric acid
C16 = Palmitic acid
C18 = Stearic acid
R = organic group
with C=C bonds
C18 = oleic acid
57
H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
Fats and Oils
58
Fats with C=C bonds are usually LIQUDS
Oleic acid: a
monounsaturated
fatty acid
C=C bond
H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
Fats and Oils
Fats with saturated acids (no C=C bonds)
are SOLIDS.
Saturated fats are
more common in
animals.
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Fats and Polar Bears
60
•Bears gorge on blubber
in the winter.
•During the summer
bears rely on stored fat
for energy.
•Burn 1-1.5 kg of fat per
day.
•Water for metabolism
comes from fat burning.
Trans Fatty Acids
61
•Oleic acid is a mono–unsaturated cisfatty acid
•Trans fatty acids have deleterious health
effects.
•Trans fatty acids raise plasma LDL
cholesterol and lower HDL levels.
C=C bond
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Fats and Oils: Saponification
Glyceryl stearate, a fat + NaOH
O
CH2 O CR
O
+ 3 NaOH
O CR
CH
O
CH2 O CR
R = —(CH2 )16CH3
CH2 OŃ H
CH OŃ H
CH2 OŃ H
Glycerol
O
+ 3 RCŃ O- Na+
Sodium stearate, a soap
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Acids + Amines --> AMIDES
N-methylacetamide
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Acids + Amines --> AMIDES
H
C
H
H
H
O
H
O
C
C
C
C
C
C
N
C
H
H
H
H
Amide link
Acetoaminophen
Tylenol, Datril, Momentum, ...
65
Alpha-Amino Acids
H2N
H
O
C
C
OH
R
Amine
H
Alanine
H3C
C
Chiral a-carbon
NH3
CO2
Acid
66
Peptides and Proteins
O
H 3N
OŠ
H CH3
Alanine
HOCH2
+
H 3N
H
OŠ
O
Serine
peptide bond
H
HOCH2
H
H 3N
O
N
H
O
OŠ
CH3
Adding more peptide links ---> PROTEIN
Polymers
• Giant molecules made by joining many
small molecules called monomers
• Average production is 150 kg per person
annually in the U.S.
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68
Polymer Classifications
• Thermoplastics (polyethylene) soften and
flow when heated
• Thermosetting plastics — soft initially
but set to solid when heated. Cannot be
resoftened.
• Other classification: plastics, fibers,
elastomers, coatings, adhesives
69
Polymer Preparation
• Addition polymers — directly
adding monomer units together
• Condensation polymers —
combining monomer units and
splitting out a small water (water)
70
Polyethylene: Addition Polymer
n H2 C
CH2
Ethylene
H
H
C
C
H
H
n
Polyethylene
A polymer with a molar mass of
1e6 has about 36,0000 units.
Mechanism of Addition
Polymerization
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Types of Polyethylene
Linear, high density PE
(HDPE)
Branched, low density
PE, LDPE
Cross-linked PE, CLPE
73
Types of Polyethylene
Polymers based on Substituted Ethylenes, CH2=CHX
CH2CH
OH
CH2CH
n
polyvinyl alcohol
CH2CH
OCCH3 n
O
polyvinyl acetate
n
polystyrene
Table 11.12: others are PVC, acrylonitrile,
polypropylene, polymethyl methacrylate
Polystyrene
• Polystyrene is nonpolar material and dissolves
in organic solvents.
• PS foam is mostly air, and when it dissolves it
collapses to a much smaller volume.
74
75
Slime!
Slime is
polyvinylalcohol
cross-linked
with boric acid
76
Condensation Polymers
O
n HOC
O
COH + n HOCH2CH2OH
terephthalic acid
O
C
ethylene glycol
O
COCH2CH2O
+ H2 O
n
Polyethylene terephthalate (PET), a polyester
77
Polyesters, PET
Jackets made from recycled
PET soda bottles
Soda bottles, mylar
film.
78
Polyesters: Mechanism
79
Polyamides: Nylon
80
Polyamides: Nylon
•Each monomer has 6 C atoms in its chain.
•A polyamide link forms on elmination of HCl
•Result = nylon 66
•Proteins are polyamides
81
Polymer Recycling Symbols
LDPE =
HDPE =
PP =
V=
Low density PE = 0.910-0.925 g/cm3
High density PE = 0.941-0.965
Polypropylene = 0.90
PVC (Vinyl chloride) = 1.30-1.58