chapter 26 skeleton notes
TRANSCRIPT
1
Organic ChemistrySelected sections Ch 26 + Ch 11
The chemistry of life and living things
The chemistry of carbon compounds
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Evolution of the field
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Why is organic chemistry important?
• To understand how we interact with– other organisms (food & nutrients, infections),– our environment (aromas, pollutants),– drugs, and – ourselves (metabolism, growth, immunity,
cancer)
• To understand how things are made, what they're made of, and how they react with each other
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Why is organic chemistry important?
• Because it is central to:ChemistryChemical BiologyBiochemistryBiologyEngineeringMaterial sciencesForensic SciencesMedicine
• To get into graduate/medical/dental school!
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Medical Application: Molecular Imaging
18F-fluorodeoxyglucose
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Organic Chemistry Components
1) Structure: The connectivity and 3-D nature of compounds
2) Theory: Structure and reactivity in terms of atoms and the electrons that bind them together
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Components (continued)
3) Synthesis: How to design new molecules – and then make them
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Organic Compounds
• Why is one element in the periodic table given its own field?– 98% of all known chemical substances are
organic
• Inorganic chemistry = the chemistry of everything else
• Nearly all pharmaceuticals are organic in nature
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Organic Compounds: Biological
OH
11-cis-retinal
Serotonin(neurotransmitter)
NH
NH2
OH
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Diagnostic iClicker Question
Which is the cis double bond in 11-cis-retinal?
OH
(a)
(b)(c)
(d)
(e)
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Organic Compounds: Medicines
Tamoxifen Viagra
OMe2N
NN NH
N
O
SO O
N
NEtO
N OH
NH
O
F
OH OH O
Lipitor
5
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Organic Compounds: Drugs
Stanozolol
NHN
OHCH3
CH3
CH3
H
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Organic Compounds: Industrial Chemicals
Indigo dye (blue jeans)NH O
NHO
NH2
NH
O
CO2H O
OMeAspartame
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Organic Compounds: Natural Products
NOH
N
MeO
Quinine
CocaineN
O
O
OO
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Alkanes
Section 26-1, 26-2
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Alkanes
• Hydrocarbons – the simplest organic compounds (CnH2n+2)
• Saturated (use all bonding e− to make single bonds)
• Methane (various representations):
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Ethane (C2H6)
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Propane (C3H8)
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Drawing Organic Molecules
• Guideline 1: Draw molecules in a Zig-Zag shape versus linear structures
• Guideline 2: You can assume there are H-atoms attached to carbon atoms in a Zig-Zag structure giving a valence of 4
vs CH3CH2CH2CH2CH2CH3
OH OHH H
H H
H
HH
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Drawing molecules (continued)
• Guideline 3: For reactions, draw out the functional groups in detail and include lone pairs (electrons)
OHO
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Advice and hints
• Be neat – messy structures lead to mistakes
• Count your carbon atoms!
• Count the substituents on carbon atoms (including implied H atoms)
• In this course, there are never more than four bonds to carbon
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Diagnostic iClicker Question
Which of the following wedge-and-dash drawings of propane is incorrect?
(a)
(c)
H
H
H
H
HHH
H
H
HH
H H
HHH
HH
H
H
H
H
HH
HH
H
H
HHH
H
(b)
(d) (e) don't know
PH
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Diagnostic iClicker Question
Which of the following wedge-and-dash drawings of propane is incorrect?
(a)
(c)
H
H
H
H
HHH
H
H H
HH
H H
H
H
HH H
H H
H HH
HH
H
H
HHH
H
(b)
(d) (e) don't know
PB
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Diagnostic iClicker Question
Which of the following wedge-and-dash drawings of propane is incorrect?
(a)
(c)
H
H
H
H
HHH
H
H
HH
H H
HHHH
H
H
H
H
H
HH
HH
H
H
HHH
H
(b)
(d) (e) don't know
JV
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Diagnostic iClicker Question
Which of the following wedge-and-dash drawings of propane is incorrect?
HH
H
H
HH
H
H HH
H H
HH
H
H
H HH
HH
HHH
HH
H
H
HHH
H
(a) (c)(b)
(d) (e) don't know
HS
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Fuels: Octane Number
Octane Number: used to indicate the resistance of a motor fuel to “knock”
p. 1084
10
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Fuels: Alcohols
Alcohols can also be used as fuels:
CH3OH(l) + 1.5O2(g) CO2(g) + 2H2O(l)
CH3CH2OH(l) + 3O2(g) 2CO2(g) + 3H2O(l)
∆Ho = -726 kJ mol-1
∆Ho = -1367 kJ mol-1
∆H°(combustion) forCH4, methane -891 kJ/molC2H6, ethane -1560 kJ/mol
http://pubs.acs.org/cen/coverstory/85/8551cover.html
Structural Diversity
Isomers, cycloalkanes
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Concept Check: Skeletal/Structural Isomerism
Concept check:
Draw structural isomers of C5H12
Skeletal or structural isomers have:
- The same molecular formula but different connectivity.
- Different physical properties.
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Concept Check: Solution
C C C C CH
HH
H
H
H
H
H
H H
HH
H C C C CH
H
H
C
H
H H
HH
HH
H
H C C CH
H
C
C
H
HH
HH
H HH
H
pentane
2-methylbutane
2,2-dimethylpropane
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Conformations of alkanes
Newman Projections
Lower E
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• Conformation: arrangement of atoms in a molecule that can be changed by simple rotation of single bonds, without breaking any bonds.
• Configuration: the permanent geometry of a molecule resulting from the spatial arrangement of its bonds.– Must break bonds to change configuration.
Conformation versus configuration
versus
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Conformations of ‘disubstituted ethane’
R'
H HR
HHH
H R'R
HHH
R' HR
HH
Staggered
Lowest E
RR'
H H
H H
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Eclipsed Conformations
H
R'
H
R
HHH
H
R'
R
HHR'
H
H
R
HH
Eclipsed
Highest E
• All eclipsed conformations have higher energy than all staggered conformations.
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Formative iClicker Question #1
Which conformation has the lowest (most favourable) energy?
R'
H HR
HH
H
H R'R
HH
R'
H
HR
HHH
H
R'R
HH
R'
H
R
HH
H
(a) (b) (c)
(d) (e)
PH
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Formative iClicker Question #1
Which conformation has the highest (least favourable) energy?
R'
H HR
HH
H
H R'R
HH
R'
H
HR
HHH
H
R'R
HH
R'
H
R
HH
H
(a) (b) (c)
(d) (e)
PB
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Formative iClicker Question #1
Which conformation has the highest (least favourable) energy?
R'
H HR
HHH
H R'R
HHR'
H
HR
HH
H
H
R'R
HH
R'
H
R
HH
H
(a) (b) (c)
(d) (e)
JV
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Formative iClicker Question #1
Which conformation has the lowest (most favourable) energy?
R'
H HR
HHH
H R'R
HHR'
H
HR
HH
H
H
R'R
HH
R'
H
R
HH
H
(a) (b) (c)
(d) (e)
HS
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Ring Structures: Cycloalkanes
CnH2n
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Molecules are not always flat: Cyclohexane
Boat Chair
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Boat conformation movie
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Boat conformation movie
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Chair conformation movie
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Chair conformation movie
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Cyclohexane Conformations
Axial vs. equatorial substituents.
Boat Chair
Equatorial H atoms are pink, axial H atoms are blue
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Ring Strain in Cycloalkanes
propane cyclopropane
• Bond angles (at C atoms) 109.5o • Bond angles (at C atoms) 60o
• H-atoms are eclipsed
Naming
Section 26-1
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Naming
• Chemistry is a visual science: Structures are key to understanding reactivity and physical properties
• Systematic nomenclature: IUPAC rules (assumed knowledge)
IUPAC: International Union of Pure and Applied Chemistry
See the supplementary information about naming in ELM for more information
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Names of common compounds
Acetone
Acetaldehyde
Formic acid
Acetic acid
Ethyl acetate
Ether
OCH2CH3
O
OH
O
H OH
O
H
O
O
CH3CH2OCH2CH3
H3C
OAcetyl group
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Common compounds (continued)
Benzene
Toluene
Phenol
Pyridine
OH
N
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Some Common Alkyl Substituents (Table 26.1)
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More alkyl names
R
R
R
R
n-butyl
sec-butyl
isobutyl
tert-butyl
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Substituents
Vinyl groups
Allyl groups
Phenyl groups
Example: Allyl acetate
R
R
R
O
O
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Diagnostic iClicker Question
What is the name of this compound?
(a) sec-butyl acetate(b) butyl methyl carboxylic acid(c) ethyl butanoate(d) isobutyl acetate(e) n-butyl acetate
O
O
PH
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Diagnostic iClicker Question
What is the name of this compound?
(a) sec-butyl acetate(b) propyl butanoate(c) ethyl butanoate(d) isobutyl acetate(e) n-butyl propanoate
O
O
PB
5757Chem1AA3
Diagnostic iClicker Question
What is the name of this compound?
(a) sec-butyl acetate(b) butyl methyl carboxylic acid(c) ethyl butanoate(d) isobutyl acetate(e) n-butyl acetate
O
O
JV
20
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Diagnostic iClicker Question
What is the name of this compound?
(a) sec-butyl acetate(b) butyl methyl carboxylic acid(c) ethyl butanoate(d) isobutyl acetate(e) n-butyl acetate
O
O
HS
Reactions of Alkanes
Section 26-2
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Concept Check
C8H18(l) + O2(g) ?
1) What are the products of the reaction at 298K?2) Write a balanced chemical equation3) Predict the signs of ∆H, ∆S and ∆G4) What type of reaction is shown?
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Concept Check: Solution
C8H18(l) + O2(g) → 8 CO2(g) + 9 H2O(l)252
∆H° = -5.48 × 103 kJ mol−1 (exothermic!)
∆So is negative
∆Go = ∆H°-T∆So, ∆Go should be negative (∆H° is large)
Reaction type: Combustion, redox
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Halogenation
CH4
X2
Light or heatCH3X + HX + CH3-CH3
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Halogenation
Initiation:
Propagation:
Termination:
H3C· + Cl·→ H3C-Cl
Cl· + Cl· → Cl-Cl
H3C· + H3C·→ H3C-CH3
Cl-Cl → 2 Cl·∆ or hν
H3C-H + Cl· → H3C· + HCl
H3C· + Cl2 → H3C-Cl + Cl·
Applicable also for F2 (often explosive), Br2, I2 (slow)
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Grignard Reagent
R XMg
Et2OR MgX
ClMg
Et2OMgCl
Look at the change in oxidation state of the Mg: Mg(0) Mg(II)
X = Cl, Br or I
Question: What gets reduced?Cl Mg2+Cl-
Bonding in alkanes
Hybridization
Section 11-3
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Review: Electronic Structure and Bonding
The following section, up to "Review: p-orbitals", is assumed knowledge and will not be discussed in class.
The Atom: A dense nucleus surrounded by a much larger extranuclear space
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Review: Principal Energy Levels
• Electrons are confined to shells defined by the principal quantum number (n)
• n = 1, 2, 3 …
• Each shell can contain 2n2 electrons
• The lower the value of n-the lower the energy of the shell (nearest to the nucleus)
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Review: Orbitals
• Shells are divided into sub-shells labelled s, p, d, f
• p, d, and f orbitals are further divided up based on their spatial orientation
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Review: Orbitals in Shells
Shell Orbitals in that shelln = 1 1sn = 2 2s, 2px, 2py, 2pz
n = 3 3s, 3px, 3py, 3pz, + 5 3d
24
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Review: Electron Configuration
Three principles/rules are used to determine the electron configuration:
Aufbau PrinciplePauli Exclusion PrincipleHund’s rule
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Review: Orbitals (subshells)
• Each type of orbital (s, p, d, f) has a distinct shape
• The shape represents the probability of finding an electron (quantum mechanics)
• Organic chemists are interested in shells 1, 2, and sometimes 3
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Review: s-orbitals
Spherical:
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Review: p-orbitals
3 of them: px, py, pz
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Example: Carbon
1s22s22p2
The outer most electrons of atoms (valence electrons) govern the chemical and physical properties
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p-Orbital Shapes
• The p-orbitals in carbon are at 90o to each other
• Atoms bonding to a carbon atom should therefore be situated at 90o to each other
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Methane - CH4
• Problem: the shape of methane is tetrahedral (AX4)
• Bond angles are 109.5o not 90o
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Hybridization
• Comes from the word hybrid which means something of mixed origin or composition
• Hybrid orbitals arise by combination of atomic orbitals within an atom
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sp3 Hybridization (section 11-3)
1s22s22p2
Ground state4 sp3 hybrid orbitals
4 atomic orbitals
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sp3 Hybridization
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sp3 Hybridization
The number of hybrid orbitals is equal to the number of combining atomic orbitals
Combine one 2s orbital and three 2p orbitals four sp3 orbitals
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Bonding-methane
Overlap of sp3 orbitals from carbon and 1s-orbitals from hydrogen
End-on (or end-to-end) overlap produces sigma (σ) bonds.
End-on overlap of sp3-orbitals also produces σ-bonds.
109.5o
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Diagnostic iClicker Question
How many σ-bonds are there in this molecule?
(a) 1(b) 2(c) 7(d) 14
H
H
H
HH
H
PH
8383Chem1AA3
Diagnostic iClicker Question
How many sp3-orbitals are there in this molecule?
(a) 1(b) 2(c) 7(d) 8
H
H
H
HH
H
PB
8484Chem1AA3
Diagnostic iClicker Question
How many sp3-sp3 σ-bonds are there in this molecule?
(a) 1(b) 2(c) 7(d) 14
JV
29
8585Chem1AA3
Diagnostic iClicker Question
How many sp3-hybridized atoms are there in this molecule?
(a) 2(b) 6(c) 8(d) 26
HS
Moving beyond alkanes:Functional Groups
8787Chem1AA3
NH2
NH
O
CO2H O
OMe
Sample Problem
What functional groups do you see?
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NH2
NH
O
CO2H O
OMe
Sample Problem: Solution
Carboxylic Acid
AmineAmide
Ester
Aromatic/Arene
8989Chem1AA3
Table 26.2
* Not a functional group
*
p. 1080
9090Chem1AA3
Table 26.2
R O R
O Ocarboxylic acid
anhydride H3C O CH3
O O
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Table 26.2
You must be able to recognize these functional groups
9292Chem1AA3
Diagnostic iClicker Question
Which functional group is not found in this molecule?
(a) aryl(b) amine(c) amide(d) phenol
PH
NH
NH2
OH
9393Chem1AA3
Diagnostic iClicker Question
Which functional group is not found in this molecule?
(a) aryl(b) hydroxyl(c) aryl halide(d) ester
PB
N OH
NH
O
F
OH OH O
32
9494Chem1AA3
Diagnostic iClicker Question
Which functional group is not found in this molecule?
(a) amide(b) ketone(c) aryl halide(d) alkene
JV
NH
HN
O
O
Cl
9595Chem1AA3
Diagnostic iClicker Question
Which functional group is not found in this molecule?
(a) aryl(b) hydroxyl(c) amine(d) amide
PB
NN NH
N
O
SO O
N
NEtO
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Synthesis
1) Functional group interconversion– ex. Converting an aldehyde to an alcohol
2) Carbon-carbon bond forming reactions– ex. Grignard reaction
H OH
O
1. CO2
2. H3O+R MgX R CO2H
33
Alkenes
Section 26-3
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Alkenes (CnH2n)
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Multiple Covalent Bonds
• Ethylene has a double bond in its Lewis structure
• VSEPR says trigonal planar shape at C
sp2 hybridization
p. 435
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100100Chem1AA3
sp2 Hybrid Orbitals (section 11-4)
Combine one 2s orbital + two 2p orbitalsthree sp2 orbitals (+ one 2p orbital left
over)
Hybrid orbital lobes pointing in the direction of an equilateral triangle: bond angles 120o
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sp2 Hybrid Orbitals
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sp2 Hybrid Orbitals
• The extra p-orbital can be used to form π-bonds
• π-bonds are covalent bonds that form by the sideways overlap of parallel p-orbitals
eclipsed p-orbitalsπ-bond
staggered p-orbitalsno π-bond
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Ethene
Section 11-4 Overlap above and below plane of atoms gives 1 π bond
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Recall: Conformations of alkanes
105105Chem1AA3
Alkenes have restricted rotation
Geometric Isomers
p. 1086
cis trans
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Fats and Oils: Triacylglycerols
O
O
O
O
R
R
O
O
R
triacylglycerol
Fat: solid at room temp.Oil: liquid at room temp.
Key Factors:• Chain length (MW)• Number of double bonds• Geometry of the double
bonds
OH
OH
OH
glycerol
(More information available on p. 1137-1139)
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Concept Check
Which of these two fatty acids has the higher melting point and why?
RO
O
Linoleic acid (R = H)
RO
O
Stearic acid (R = H)
108108Chem1AA3
Concept Check: Solution
RO
O
Linoleic acid (R = H)
RO
O
Stearic acid (R = H)
mp = -5oC
mp = 70oC
Less efficient packing because of kink in chain geometry, therefore weaker intermolecular forces and lower melting point.
Straight chain allows more efficient packing, therefore strongerintermolecular forces and higher melting point.
37
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Impact of Geometry
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The E,Z System of Nomenclature
• Need a new system• Higher priority higher atomic number
p. 1106
Z isomer E isomer
111111Chem1AA3
Concept Check
OMe2NOMe2N
Label the tamoxifen isomers as E or Z:
Z E
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Formative iClicker Question #2
Which molecule has an E configuration?
F
ClF
Cl(a) (b) (c)
(d) (e)
PH
113113Chem1AA3
Formative iClicker Question #2
Which molecule has an E configuration?
(a) (b) (c)
(d) (e)
F
FF
F
PB
114114Chem1AA3
Formative iClicker Question #2
Which molecule has an E configuration?
(a) (b) (c)
(d) (e)
Cl
ClCl
Cl
JV
39
115115Chem1AA3
Formative iClicker Question #2
Which molecule has an E configuration?
Cl
ClF
Cl F(a) (b) (c)
(d) (e)
F
HS
116116Chem1AA3
Degree of Unsaturation
• A hydrocarbon with one π-bond or ring has two fewer H-atoms than a linear alkane; it is said to have “1 degree of unsaturation”
• The molecular formula of a hydrocarbon can be used to determine the number of π-bonds and/or rings in a compound.
• The "degree of unsaturation" (d.o.u.) can be calculated using:
d.o.u. = (2n + 2 - m) / 2 (m = # of H-atoms, n = # of C-atoms)
117117Chem1AA3
Degree of Unsaturation (d.o.u.)
• Rings count as one d.o.u. • Double bonds count as one d.o.u. • Triple bonds count as two degrees of
unsaturation
• d.o.u. does not give the type or number of each type of unsaturation (ring, π bond); this is determined using spectroscopic techniques (2nd
year)
• Note: a molecule can be saturated yet have a degree of unsaturation (e.g., cyclohexane)
40
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Diagnostic iClicker Question
Which molecule has the highest degree of unsaturation?
(a) (b) (c)
PH
119119Chem1AA3
Diagnostic iClicker Question
Which molecule has the highest degree of unsaturation?
(a) (b) (c)
PB
120120Chem1AA3
Diagnostic iClicker Question
Which molecule has the lowest degree of unsaturation?
(a) (b) (c)
JV
41
121121Chem1AA3
Diagnostic iClicker Question
Which molecule has the lowest degree of unsaturation?
HS
(a) (b) (c)
Reactions involving alkenes
Section 26-3
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Addition Reactions
Markovnikov’s rule: the H atom ends up attached to the carbon atom of the double bond that has the most hydrogen atoms to start with.
Not observed
p. 1087-1088
42
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Explanation of Markovnikov’s rule
H Br
H
+
+
H
2o carbocation - less stable
3o carbocation - more stable
Br -
X
Br -
H
Br
haloalkane product
δ+δ-
125125Chem1AA3
Curly arrows
• The curly arrow represents electrons moving from the alkene π-bond to the proton of HBr, forming a C-H bond.
• We will examine this in more detail in nucleophilic substitution reactions (Section 26-11)
H Brδ+δ-
126126Chem1AA3
Carbocation stability
Stability:
Why do alkyl substituents increase cation stability?
Steric:
The cationic carbon rehybridizes from sp3 to sp2, relieving the steric clash between substituents
H3C+ < < <
methyl 1° 2° 3°< < <
Br
H3CH3C CH3
Br -
CH3H3C
H3C
43
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Carbocation stability
Why do alkyl substituents increase cation stability?
Electronic:
Alkyl substituents are electron donating compared with H. Donating electrons to an electron deficient (positively charged) centre stabilizes it.
= a permanent electric dipole
CH3
CH3H3C
δ-δ+
128128Chem1AA3
Formative iClicker Question #3
What is the expected product, according to Markovnikov's rule?
HBr
(a)
Br
BrBr
(b)
(c)
Br
(d)
Br
PH
129129Chem1AA3
Formative iClicker Question #3
What is the expected product, according to Markovnikov's rule?
HI
(a)
I
II
(b)
(c) (d)
I
I
PB
44
130130Chem1AA3
Formative iClicker Question #3
What is the expected product, according to Markovnikov's rule?
HBr
(a)BrBr
(b)
(c) (d)
Br Br
JV
131131Chem1AA3
Formative iClicker Question #3
What is the expected product, according to Markovnikov's rule?
HCl
(a)
Cl
ClCl
(b)
(c) (d)
Cl
Cl
HS
132132Chem1AA3
Hydration Reaction
• Addition is favoured (forward reaction) in dilute acid
• Elimination is favoured (reverse reaction) in concentrated acid
45
133133Chem1AA3
Hydration also follows Markovnikov's rule
HO
HH2O
H
+H2O
H3O+
H
+OH
H
OH
H
H
HO
H3O+
JV?
134134Chem1AA3
Reduction of Alkenes
HH
H H
catalyst
Hydrogenation
135135Chem1AA3
Application: Hydrogenation of Natural Products
CH2OC(CH2)7CH
CHOC(CH2)7CH
O
CH(CH2)7CH3
CH(CH2)7CH3
O
CH2OC(CH2)7CH
O
CH(CH2)7CH3
3H2
Ni catalyst heat
CH2OC(CH2)16CH3
CHOC(CH2)16CH3
O
O
CH2OC(CH2)16CH3
O
Unsaturated vegetable oil(olein-liquid)
Solid cooking fat-shortening (stearin, solid)
(More information available on p. 1137-1139)
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Partial Hydrogenation
RO
O
RO
O
H2 (1 equiv.)
catalyst
H
Hmixture
saturated at either double bond, e.g.
137137Chem1AA3
cis versus trans fatty acids
cis-9-octadecenoic acid(Oleic acid)
trans-9-octadecenoic acid(Elaidic acid)
Alkynes
Section 26-3
47
139139Chem1AA3
Alkynes
According to VSEPR, alkynes are linear
p. 1085
140140Chem1AA3
sp Hybrid Orbitals
• Combine one 2s orbital + one 2p orbital two sp orbitals (+ two 2p orbitals left over)
sp hybridization
Section 11-4, p. 436
sp hybridization
141141Chem1AA3
sp Hybrid Orbitals
48
142142Chem1AA3
Acetylene: Orbitals
• Acetylene, C2H2, has a triple bond.• Linear at carbon
Reactions of Alkynes
144144Chem1AA3
Reduction of Alkenes and Alkynes
HH
H H
catalyst
CH3CH2C CCH3 + H2
CH3
HH
EtLindlar's catalyst
CH3CH2C CCH3 + H2Pd/C
CH3CH2CH2CH2CH3
Cis isomer only!
p. 1088
49
The Carbonyl Group:ketones and aldehydes
Section 26-6
146146Chem1AA3
Examples
Ketones
Aldehydes
O
Acetone Methyl ethyl ketone (MEK) Testosterone
O
OHCH3
H3C
O
H
O
H
O
H H
O
Formaldehyde Benzaldehyde Cinnamaldehyde
p. 1094-1095
147147Chem1AA3
Structure and Polarity
H3C CH3
O122o
116o
122o
H CH3
O124o
118o
118o
H H
O121o
118o
121o
R R
Oδ+
δ-
50
Synthesis and reactions of aldehydes and ketones
Section 26-5, 26-6
149149Chem1AA3
Synthesis
Oxidation of alcohols:
HOH
O
OH O
Oxidation: Addition of an oxygen atom or removal of (a molecule of) hydrogen
[O] = Oxidizing agent
[O]
[O]
150150Chem1AA3
Primary, Secondary & Tertiary Alcohols
R CH2 OH
R CH OHR'
R C OHR'
R''
Primary (1o)
Secondary (2o)
Tertiary (3o)
51
151151Chem1AA3
Oxidation
• Primary alcohol aldehyde carboxylic acid
• Secondary alcohol ketone
• Tertiary alcohol no reaction– a C-C bond would have to break in order for oxidation
to occur
HOH
O
OH
O
OH O
152152Chem1AA3
Formative iClicker Question #4
What is the expected product of oxidation of 2,2-dimethylpropanol?
(a) 2,2-dimethylpropanoic acid(b) 2,2-dimethylpropanone(c) 2-methyl-2-propanal(d) no reaction
PH
153153Chem1AA3
Formative iClicker Question #4
What is the expected product of oxidation of s-pentanol?
(a) methyl butyl ketone(b) 2-pentanone(c) pentanoic acid(d) none of the above
PB
52
154154Chem1AA3
Formative iClicker Question #4
What is the expected product of oxidation of isopentanol?
(a) methyl butyl ketone(b) 2-pentanone(c) 4-methyl pentanoic acid(d) none of the above
JV
155155Chem1AA3
Formative iClicker Question #4
What is the expected product of oxidation of 2-methylbutanol?
(a) 2-methylbutanoic acid(b) 2-methylbutanone(c) s-pentanoic acid(d) none of the above
HS
156156Chem1AA3
Oxidizing Agents
• Commonly metals in high oxidation states (transfer of 2 to 4 electrons)
e.g., MnO4-, Cr2O7
2- (KMnO4, K2Cr2O7)
• Usually done in acid or base to facilitate electron transfer
• Pyridinium chlorochromate (PCC)– Specific for oxidizing 1o alcohols aldehydes
53
157157Chem1AA3
Metabolism of Alcohol: Detoxification
ethanol rapidly distributes from blood to tissues/organs brain
two-step oxidation of ethanol acetaldehyde acetic acid
acetic acid is eliminated by kidneys or metabolized into energy
Enzymatic Detoxification by Two-step Oxidation
"One of the disadvantages of wine is that it makes a man mistake words for thoughts." -- Samuel Johnson
158158Chem1AA3
Metabolism of Alcohol: Detoxification
Enzymatic Detoxification by Two-step Oxidation
Alcohol Dehydrogenase
AcetaldehydeDehydrogenase
OH + NAD+
H
O+ NADH + H+
+ NAD+ + NADH + H+
OH
O
H
O
oxidizing agent toxic intermediate
non-toxic final product
159159Chem1AA3
Addition Reactions to the Carbonyl Group
Reduction: NaBH4 is a source of H- (hydride)
H OH
O 1. NaBH4
2. H3O+
O 1. NaBH4
2. H3O+
OH
aldehyde 1o alcohol
2o alcoholketone
p. 1096
54
Synthesis and Reactions of Carboxylic Acids and
Derivatives
Section 26-7
161161Chem1AA3
Examples
p. 1097
162162Chem1AA3
Carboxylic Acid: Structure
55
Synthesis and Reactivity
Section 26-7
164164Chem1AA3
Carboxylic acids
Weak acids:
OH
O
O-
O+ H3O++ H2O Ka = 1.4x10−5
OH
O
O-
O+ H3O++ H2ONaOH Na+ + H2O
R Cl
O
R O
O
R R NHR
O
R O
O
R
O
Acid chloride Ester AmideAnhydride
Derivatives:
165165Chem1AA3
Preparation of Esters
OH
O
OCH2CH3
OH++ CH3CH2OH + H2O
• Fischer Esterification
• Acid catalyst
• Condensation reaction
p. 1098
56
166166Chem1AA3
Hydrolysis of Esters
OH
O
OCH2CH3
O H++ CH3CH2OH+ H2O
• Reverse of previous reaction
• Also requires acid catalyst
167167Chem1AA3
Acid chlorides
Acid chloride
R Cl
O
R NH
OR NH2 R
+ HCl+
R Cl
O
R O
OR OH
R+ HCl+
R OH
O R NH2
R O-
O
RH3N+Carboxylic acid Acid-base
reaction
amide
ester
168168Chem1AA3
Acetyl Group
p. 1097
57
Synthesis
Section 26-12
170170Chem1AA3
Concept Check: Synthesis
Fill in the missing reagents:
OHO
171171Chem1AA3
Concept Check: Solution
OHO 1. NaBH4
2. H3O+
conc. H2SO4, ∆
58
172172Chem1AA3
Formative iClicker Question #4
What are conditions i and ii?
O
OHi
ii
PH
PCCNaBH4(d)KMnO4NaBH4(c)
10% H2SO4PCC(b)KMnO4Lindlar's catalyst(a)
iii
173173Chem1AA3
Formative iClicker Question #4
What are conditions i and ii?OH
i
ii
PB
10% H2SO4conc. H2SO4(d)H2/Pd-C10% H2SO4(c)
10% H2SO4PCC(b)conc. H2SO410% H2SO4(a)
iii
174174Chem1AA3
Formative iClicker Question #4
What are conditions i and ii?
Cl
i ii
JV
HClLindlar's catalyst(d)
Cl2H2/Pd-C(c)
HClH2/Pd-C(b)
Cl2PCC(a)
iii
59
175175Chem1AA3
Formative iClicker Question #4
What are conditions i and ii?i ii
HS
H2/PdLindlar's catalyst(d)
Lindlar's catalystH2/Pd-C(c)
PCCKMnO4(b)
PCCH2/Pd-C(a)
iii
Substitution Reactions and Mechanisms
Section 26-11
177177Chem1AA3
Chemical Reactions
• Charge attraction draws molecules together
• In organic chemistry, there is often not a cation reacting with an anion
• It is more common to have a charged reagent be attracted to an organic compound that has a dipole– e.g., NaCN + acetone (polarized C=O bond generating
an electropositive carbon atom that attracts the CN-)
60
178178Chem1AA3
Chemical Reactions Continued
• The reagent does not necessarily need to be charged: Lone electron pairs would also be attracted to a dipole
179179Chem1AA3
Chemical Reactions
• The majority of reactions in organic chemistry involve the flow of electrons from one molecule to another
• nucleophile (nucleus loving) = electron donor = Lewis base
• electrophile (electron loving) = electron acceptor = Lewis acid
p. 1108
180180Chem1AA3
Chemical Reactions
• In most organic reactions the orbitals of the nucleophile and electrophile are directional therefore the two orbitals must be correctly aligned for a reaction to occur
61
181181Chem1AA3
Substitution Reactions at sp3 Hybridized Carbon
Charged nucleophiles
Neutral nucleophiles
182182Chem1AA3
Mechanism
• The flow of electrons between a nucleophile and electrophile can be represented by a double-headed curly arrow
• The result of the movement is to form a bond between an electrophile and a nucleophile
NH3 E+
NH3 E+ N EH
HH
+
183183Chem1AA3
Mechanism (continued)
• The arrow tail starts at the source of the moving electrons and the arrow head indicates its final destination
NH3 E+
62
184184Chem1AA3
SN2 Mechanism
Rate = k[OH-][CH3Cl]
S = substitution; N = nucleophilic, 2 = bimolecular
p. 1111
185185Chem1AA3
Diagnostic iClicker Question
Cl- + CH3Br CH3Cl + Br-
CH3ClBr-(d)
Br-Cl-(c)
Cl-CH3Br(b)
CH3BrCl-(a)
ElectrophileNucleophile
PH
What are the nucleophile and the electrophile in this reaction?
186186Chem1AA3
PB
Diagnostic iClicker Question
H3C-NH2 + CH3Cl H3C-NH-CH3 + HCl
H+Cl-(d)
Cl-CH3NH2(c)
CH3ClCH3NH2(b)
H3C-NH-CH3CH3Cl(a)
ElectrophileNucleophile
What are the nucleophile and the electrophile in this reaction?
63
187187Chem1AA3
JV
Diagnostic iClicker Question
What are the nucleophile and the electrophile in this reaction?
H3C-NH2 + CH3Cl H3C-NH-CH3 + HCl
H+H3C-NH-CH3(d)
CH3ClCH3NH2(c)
Cl-CH3Cl(b)
H3C-NH-CH3CH3NH2(a)
ElectrophileNucleophile
188188Chem1AA3
HS
Diagnostic iClicker Question
What are the nucleophile and the electrophile in this reaction?
Cl-Br-(d)
CH3ClCl-(c)
Cl-CH3Cl(b)
Br-Cl-(a)
ElectrophileNucleophile
Cl- + CH3Br CH3Cl + Br-
189189Chem1AA3
SN2 Mechanism
More on mechanisms in the next section
δ- δ-
64
190190Chem1AA3
SN2: Inversion of Configuration
191191Chem1AA3
SN1 Mechanism (unimolecular)
p. 1112
192192Chem1AA3
SN1 Mechanism
Rate = k [(CH3)3CBr]slow
fast
fast
65
193193Chem1AA3
SN1 versus SN2
• The mechanism depends on many factors, but as a general rule of thumb:
• 1o electrophile = SN2– less stable carbocation intermediate, less steric
hindrance to nucleophilic attack• 2o electrophile = ?
– hard to predict (you will see this next year)• 3o electrophile = SN1
– more stable carbocation intermediate, more steric hindrance to nucleophilic attack
194194Chem1AA3
Formative iClicker Question #5
Rank the likelihood of the following compounds to undergo SN2 nucleophilic substitutions:
(a) i < ii ≈ iii (b) i > ii > iii (c) i > ii ≈ iii(d) i ≈ ii > iii
ClCl
Cl
i ii iii
PH
195195Chem1AA3
Formative iClicker Question #5
Rank the likelihood of the following compounds to undergo SN2 nucleophilic substitutions:
(a) iii ≈ ii < i (b) i ≈ ii > iii(c) i > iii > ii(d) ii > i < iii
Cl ClCl
i ii iii
PB
66
196196Chem1AA3
Formative iClicker Question #5
Rank the likelihood of the following compounds to undergo SN2 nucleophilic substitutions:
(a) iii ≈ ii > i (b) i ≈ ii > iii(c) i > ii ≈ iii(d) ii > i < iii
ClCl
Cl
i ii iii
JV
197197Chem1AA3
Formative iClicker Question #5
Rank the likelihood of the following compounds to undergo SN2 nucleophilic substitutions:
(a) i ≈ iii < ii (b) i ≈ ii < iii(c) i < ii > iii(d) ii ≈ i > iii
Cl
Cl Cl
i ii iii
HS