C341 Fall 2011/Chapter 1
Welcome to C341!!
Chapter 1 & 2:
Review of General Chemistry
What will we do today?
1.
Review of the syllabus together.
2.
Discuss course structure and textbook.
 You will use the entire textbook between C341, C342 and C343.
3.
Set realistic expectations for work load.
4.
Start reviewing general chemistry concepts in chapter 1.
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C341 Fall 2011/Chapter 1
Pertinent subjects in C117 that lead to success in C341:
1. Periodic table; charges on ions and atoms by group
2. Types of bonding; ionic versus covalent bonds, e.g. NaOCH3, NaH
3. Lewis structures; organic line drawings, understanding ball and stick
drawings with wedges and dashes; bond polarity and molecular
polarity; functional groups would be nice.
4. Hybridization, shape, and VSEPR.
5. Resonance structures with organic molecules, not just carbonate,
sulfate and nitrate.
6. Intermolecular forces, physical properties and solubilities in water
versus hydrocarbons.
7. Thermochemistry; bond energies, potential energy diagrams and
enthalpy changes.
8. Kinetics; one‐step versus two‐step reactions, reaction mechanisms and
their rate laws.
9. Equilibrium; equilibrium constants; Le Châtelier’s principle; product‐
favored versus reactant‐favored.
10. Thermodynamics, ΔG and spontaneity; product‐favored versus
reactant‐favored.
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C341 Fall 2011/Chapter 1
Chapter 1 & 2 outline:
1. Lewis Structures for organic compounds
 Line Drawings ‐ drawing organic compounds
 Formal charge
 Resonance, resonance contributors & bond order
2. Bond Angles & Shapes
3. Hybridization
4. Bond Polarity & Molecular Polarity
 Polar & Non‐polar compounds
5. Intermolecular forces
6. Predicting physical properties based on intermolecular forces
7. Predicting solubility based on intermolecular forces
 Solubility of molecules
8. Functional Groups – may be new material for some people
You should do all the problems within the chapter and at the end of the chapter.
But if you who want to do the minimal amount of work:
Chapter 1: 1.34 (use line drawings), 1.39, 1.45, 1.46, 1.48, 1.52, 1.53, 1.56 (draw
this as a line drawing), 1.61, 1.63, 1.64
Chapter 2: 2.43‐2.50, 2.53, 2.55‐2.58, 2.61, 2.63‐2.66
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C341 Fall 2011/Chapter 1
1. Lewis Dot Structures from Condensed Structural Formulae
A Lewis Structure depicts the structure of a compound by its arrangement of
atoms with its neighbors, bonds that exist, and the presence of lone pairs.
 Molecules share electrons in order to achieve a closed shell or a total of 8
electrons surrounding each atom (octet rule).
 Hydrogen is the only atom who is content with only 2 electrons.
 Don’t forget that third row atoms or lower can exceed an octet, e.g. S and P.
CH3COCH2NH2
CH3CO2CHCHCH3
CH3CHOHCH2CONHCH2CH3
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C341 Fall 2011/Chapter 1
Line Drawings
Amoxicillin:
Estrogen (female steroid):
Zingerone (pungent extract from ginger):
Capsaicin (you and a neighbor come up with the formula for this):
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C341 Fall 2011/Chapter 1
Constitutional Isomers:
Single bonds are axes of rotation to form conformers:
Constitutional isomers of hexanes:
Draw several constitutional isomers for C4H10O:
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C341 Fall 2011/Chapter 1
Formal Charge
H
O
O
S
O
N
N
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C341 Fall 2011/Chapter 1
Resonance Structures:
o Some molecules cannot be adequately represented by a single Lewis structure.
o Resonance structures are two Lewis structures having the same placement of
atoms but a different arrangement of electrons.
o Resonance allows certain electron pairs to be delocalized over several atoms,
and this delocalization adds stability to the molecule.
o A molecule with two or more resonance forms is said to be resonance
stabilized.
o Resonance structures are possible if electrons are in conjugation.
Rule 1:
All resonance structures must have the same number of valence e’s.
Rule 2:
The octet rule must be obeyed and not exceeded (esp. for C, O, N,& H).
Rule 3:
Nuclei do not change positions in space between resonance structures.
Rule 4:
Sigma bonds must not be broken and the skeletal structure rearranged.
Conjugation =
A series of alternating single and multiple bonds with overlapping p orbitals.
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C341 Fall 2011/Chapter 1
Organic Resonance structures (anions, cations & neutral compounds):
Recognizing allylic and vinylic positions:
Indicate all chlorides as either allylic and vinylic:
Cl
Cl
Cl
Cl
Cl
Circle all the allylic lone pairs:
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C341 Fall 2011/Chapter 1
O
O
O
N
H
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C341 Fall 2011/Chapter 1
Common Mistakes
Localized vs. delocalize electrons. Generally, lone pars adjacent to a C=C double
bond are capable of resonance, but not in this case.
Your turn to practice with a neighbor:
N
N
O
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C341 Fall 2011/Chapter 1
2.
Bond angles & shapes
VSEPR Theory predicts the MOLECULAR SHAPE & ANGLES
FACT:
Molecules bond such that all the regions of electron density around a central
atom are as far away from each other as possible.
Determine the shape, not geometry, for the following atoms:
O
O
O
O
cocaine
N
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C341 Fall 2011/Chapter 1
3.
Hybridization, σ & π‐bonds
Single bonds –
 End‐to‐end overlap of orbitals of two ‘s’ orbitals.
 Electron density is found along the bond axis in between the atoms.
 The first bond between any 2 atoms is always a σ‐bond.
Multiple bonds –
 Multiple bonds arise from a combination of a σ ‐bond and π–bonds.
 π ‐bonds have their electron density above and below the bond axis.
 π ‐bonds arise from the parallel overlap of unhybridized p orbitals.
 π ‐bonds are weaker than σ‐bonds.
 Two π ‐bonds on the same atom are made in perpendicular planes.
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C341 Fall 2011/Chapter 1
Determine the hybridization for the following atoms:
O
H3CO
Co-enzyme Q-10
H3CO
O
Hybridization of an amide?
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C341 Fall 2011/Chapter 1
Orbital overlap descriptions:
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C341 Fall 2011/Chapter 1
4.
Bond Polarity & Molecular Polarity
Electronegativity =
The relative ability of an atom to attract electron density to itself during a covalent
bond (expressed on a scale relative to “F” being assigned a number of 4.0)
Expressions of bond polarity
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C341 Fall 2011/Chapter 1
Which of the following bonds are polar? How do we illustrate that a
bond is polar and which direction is the electron density flowing?
H—Br
C—O
C—H
O—H
B—H
C—I
Bond polarity relates to acidity in chapter 3:
H2B—H
H3C—H
H2N—H
HO—H
H—F
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C341 Fall 2011/Chapter 1
Polar molecules versus non‐polar molecules
A. Use electronegativity values to predict bond dipoles (assign δ+ and δ ‐).
B. Use the VSEPR method to predict the molecular shape.
C. From the molecular shape, determine whether bond dipoles cancel to give a
non‐polar molecule or combine to produce a resultant dipole moment for
the molecule.
Start to learn these organic solvents below (they will be tested on quiz 1/exam 1).
Which are polar and non‐polar?
O
O
O
CH3OH
S
DMSO
dimethly sulfoxide
acetone
O
OH
acetic acid
H
H3C
N
DMF
(dimethyl
formamide)
methanol
acetonitrile
O
THF
(tetrahydrofuran)
CH2Cl2
methylene chloride
CH3
O
diethyl ether
C
hexane
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toluene
N
C341 Fall 2011/Chapter 1
Where do you draw the line between polar vs. non‐polar?
Dielectric constant = the property of a dielectric that determines the electrostatic
energy per unit volume for unit potential gradient.
WHAT does that mean?
What is considered a polar solvent based on dielectric constant?
Name
Structure
bp, oC
dipole moment
dielectric
constant
water
H‐OH
100
1.85
80
formic acid
100
1.41
58
diemthyl sulfoxide (DMSO)
189
3.96
47.2
N,N‐dimethylformamide
(DMF)
153
3.82
38.3
acetonitrile
81
3.92
36.6
methanol
CH3‐OH
68
1.70
33
ethanol
CH3CH2‐OH
78
1.69
24.3
56
2.88
20.7
97
1.68
20.1
80
2.78
18.5
acetone
1‐propanol
CH3CH2CH2‐OH
methyl ethyl ketone
1‐butanol
CH3CH2CH2CH2‐OH
118
1.66
17.8
methylene chloride (DCM)
CH2Cl2
40
1.60
9.08
tetrahydrofuran (THF)
66
1.63
7.52
acetic acid
118
1.74
6.15
ethyl acetate
78
1.78
6.02
35
1.15
4.34
80
0
2.28
diethyl ether
CH3CH2OCH2CH3
benzene
carbon tetrachloride
CCl4
76
0
2.24
hexane
CH3(CH2)4 CH3
69
‐‐‐‐
2.02
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C341 Fall 2011/Chapter 1
5.
Intermolecular Interactions
 Intramolecular forces (covalent & ionic forces) are strong.
 Intermolecular forces are comparatively weak. But these intermolecular
forces add up to make an “overall” significant contribution to the overall
physical property of a substance.
Review the types of intermolecular forces:
o
o
o
o
Relative strengths
H‐bonding (HBA & HBD)
10‐40 kJ/mol
Dipole‐dipole forces (DD)
5‐25 kJ/mol
London dispersion forces (LDF)
0.5‐40 kJ/mol
Induced dipole
2‐10 kJ/mol
Compare to:
o Ionic
o Covalent
o Metallic
Relative strengths
400‐4000 kJ/mol
150‐1100 kJ/mol
75‐1000 kJ/mol
Why is understanding intermolecular forces (IMF) important?
 Solubility in solvents (hydrophobic vs. hydrophilic)
 Physical properties like boiling and melting points (e.g. the stronger the
intermolecular forces the higher the boiling point)
 Three dimensional structures (consider the tertiary structure of a protein)
 Reactivity between species
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C341 Fall 2011/Chapter 1
Non‐polar molecules tend to experience predominately:
London Dispersion Forces (a.k.a. van der Waals forces) WEAK, attractive forces
between molecules with TEMPORARY DIPOLE.
What dictates extent of LDF?
What is polarizability? Which are more polarizable: cations or anions?
Compare the isomers of hexane – they have the same number of atoms and
electrons. Which has higher LDF and why?
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C341 Fall 2011/Chapter 1
Polar organic molecules tend to experience:
Dipole‐dipole forces: attractive forces between molecules with a PERMANENT
DIPOLE.
Demonstrate how acetone exhibits a DD interaction (you must understand polar
bonds and dipoles first).
H‐bonding: an especially strong dipole‐dipole attraction forces between
molecules that have X—H bonds (X = O, N, F only).
What are HBA and HBD? Demonstrate an H‐bonding interaction:
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C341 Fall 2011/Chapter 1
6.
Predicting physical property trends in organic chemistry
Work with your neighbors to put the following compounds in order of
boiling point.
Also put in an example of the methyl butyl amine.
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C341 Fall 2011/Chapter 1
7.
Polarity Effects on Solubility (“Like dissolves like”)
 Which would you predict to be soluble in water?
 Which would you predict to be NOT water soluble?
 Which are protic?
 Which are aprotic?
O
O
O
CH3OH
S
DMSO
dimethly
sulf oxide
acetone
O
O
H
H3C
C
N
N
DMF
(dimethyl
formamide)
methanol
acetonitrile
CH3
O
OH
diethyl ether
acetic acid
THF
(tetrahydrofuran)
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hexane
toluene
C341 Fall 2011/Chapter 1
What type of solvent would you use to dissolve cholesterol?
(Ask me now about the 5‐carbon rule…)
H
H
HO
H
cholesterol
Micelles:
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C341 Fall 2011/Chapter 1
Predict the solubility of the following molecules:
HO
O
OH
N
O
HO
NH2
N
Vitamin B6
Novocain (procaine)
OH
O
O
O
OH
5
HO
OH
O
Vitamin C
Vitamin K
HO
O
HO
Vitamin E
Vitamin D
Cl
H3CHN
Cl
N
Cl
O
N
Valium (diazepam)
Zoloft – antidepressant
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C341 Fall 2011/Chapter 1
8. Functional Groups:
 Organic Chemistry is the study of carbon and the compounds that contain
carbon (also contain H, N, O & S)
 Organic compounds are organized by classes called functional groups.
 A functional group is an atom or a group of atoms with characteristic
chemical and physical properties. It is the reactive part of the molecule.
 The different functional groups refer to compounds that have similar
properties with similar chemical bonds.
 Functional groups differ based on their component heteroatoms or pi‐bonds.
 Heteroatoms have lone pairs and create electron‐deficient sites on carbon.
 Many molecules have several functional groups in one molecule!
Capsaicin:
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C341 Fall 2011/Chapter 1
Hydrocarbons
Hydrocarbons contain carbons and hydrogens; generic formula of R—H (ask me
what the R means).
Functional Characteristic
group
Alkanes
Contains all C—C
single bonds
Alkenes
Contains at least
one C=C double
bond
Alkynes
Contains at least
one C≡C triple
bond
Arenes
Contains at least
one benzene ring
Examples
CH3
OH
Toluene
Naphthalene = moth balls
Phenol
NO2
NO2
NO2
O2N
CH3
TNT = trinitrotoluene
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NO2
O2N
OH
Picric acid = insecticide
C341 Fall 2011/Chapter 1
FG
Alcohol
Thiol
Characteristic
R—OH
Examples
Primary (1o)
Secondary (2 o)
Tertiary (3 o)
Primary (1o)
Secondary (2 o)
Tertiary (3 o)
R—SH
Ether
R—O—R
Thioether
R—S—R
S
S
Amines
R—NH2
Primary (1o)
Nitriles
R—C≡N
Alkyl
Halides
R—X,
X = halogen
Primary (1o)
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Secondary (2 o)
Secondary (2 o)
Tertiary (3 o)
Tertiary (3 o)
C341 Fall 2011/Chapter 1
Carbonyl containing compounds:
C=O is called a “carbonyl group”
O
O
C
C
R
H
R
Aldehyde
R
Acid chloride
R
Ketone
O
O
O
C
C
C
OH
R
Carboxylic acid
OR
R
Ester
Identify correct functional groups in the following molecules.
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NH2
Amide
C341 Fall 2011/Chapter 1
Working with a neighbor/after class, determine the following:
 Functional groups?
 Soluble (S) or insoluble (N) in water?
 IMF? LF (London Forces), DD (dipole‐dipole), HBA (hydrogen bond
acceptor), and HBD (hydrogen bond donor) as appropriate.
CH3
O
OH
O
OH
S or N
S or N
S or N
S or N
LF
LF
LF
LF
DD
DD
DD
DD
HBA
HBA
HBA
HBA
HBD
HBD
HBD
HBD
O
O
N
O
N
H
S or N
S or N
S or N
S or N
LF
LF
LF
LF
DD
DD
DD
DD
HBA
HBA
HBA
HBA
HBD
HBD
HBD
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HBD