Upload
yan-li
View
214
Download
0
Embed Size (px)
Citation preview
8/3/2019 1. Review of Organic Chemistry I
1/64
Your C342 Team: Part I
This course will be team taughtwe will manage theentire course as a team, including lectures, quizzes and
exams1
Prof. Martha G. Oakley Prof. Laura C. Brown
8/3/2019 1. Review of Organic Chemistry I
2/64
8/3/2019 1. Review of Organic Chemistry I
3/64
C342 Organic Chemistry II
Time
Understanding
A Challenging Course
Many of life's failures are people who did not realize how close
they were to success when they gave up. ~ Thomas Edison
8/3/2019 1. Review of Organic Chemistry I
4/64
Discussions: Attend Any You Like
You may attend more than one discussion per week, if space
You may earn up to 10 bonus points over the semester for
attending office hours (max 1 per week) 4
8/3/2019 1. Review of Organic Chemistry I
5/64
OFFICE HOURS
We will hold 12 office hours weekly beginning next week Professor Oakley will hold office hours this week from
3:00-4:00 on Tuesday and from 4:00 to 5:05 onThursday, Simon Hall (across from Jordan), Room 320B.
Professor Brown will hold office hours this week onMonday 9-10 am and Wednesday from 12:20-1:20 in
Chemistry A112
Regular office hours begin next week.
5
8/3/2019 1. Review of Organic Chemistry I
6/64
Grading
Quizzes (see syllabus for dates) best 3 out of 4 (100 pts) Early quizzes available only for university sanctioned
events, etc.
Exams 3 x 2 hr exams; Tues evenings (150 pts each) Final Exam (300 pts) Drop lowest exam or of final grade, whichever is lowest YOU ARE RESPONSIBLE FOR READING THE
SYLLABUS
6
8/3/2019 1. Review of Organic Chemistry I
7/64
Grading Cutoffs
The instructors do not grade on a curve (A) understands the material well andcan apply it
creatively to new situations. Cutoff for an A- no higher than 90%. (B) Good, solid understanding of the material Cutoff for a B- no higher than 75% (C) Major gaps in understanding Cutoff for a C- no higher than 60%. (D or F) Still larger gaps
7
8/3/2019 1. Review of Organic Chemistry I
8/64
Active Learning
You should be thinkingduring class We will do lots of problem-solving in class We will call on students to help us work problems You should be trying to work the problem at the same
time as the student who has been called on
You get a bonus point every time you participate right orwrong
There are no other ways to earn bonus points, except fordiscussion attendance
8
8/3/2019 1. Review of Organic Chemistry I
9/64
Courtesy in Class
This is a large room and there are a lot of people in it. Whispering in class makes it difficult for others to hear
the lectures
This class costs a lot of money! Lecture attendance is optional in this course Should you choose to attend lecture, we expect you to
be courteous to us and to your classmates
If we are slowed or cannot continue because of noise,you are responsible forallthe material we would havecovered without the noise.
9
8/3/2019 1. Review of Organic Chemistry I
10/64
Review of Organic Chemistry I
Work practice problems on Oncourse (Resources,Practice Problems for Quiz 1)
Read Chapter 4.2-4.6 (Review)Work problems 4.3, 4.16, 4.17, 4.18, 4.19, 4.22,
4.29, 4.30, 4.31
10
8/3/2019 1. Review of Organic Chemistry I
11/64
Lewis Structures and Formal Charge
11
8/3/2019 1. Review of Organic Chemistry I
12/64
B. Write a Lewis structure for diazomethane
(CH2N2) and assign each atom a formal charge
(connectivity as shown)
12
8/3/2019 1. Review of Organic Chemistry I
13/64
II. Curved Arrows
B. Move from electron source to electron sink
source: ________ charge or _____________
sink: __________ charge or partial _____________
13
8/3/2019 1. Review of Organic Chemistry I
14/64
III. Resonance
A. Provide appropriate curved arrows to show how togenerate additional resonance structures (if possible)
O
O
O
14
8/3/2019 1. Review of Organic Chemistry I
15/64
B. How many resonance structures can you draw for the
benzyllic cation (5 possible)? Show the electron flow
between each one.
15
8/3/2019 1. Review of Organic Chemistry I
16/64
IV. Curved Arrows in Reaction Mechanisms
16
8/3/2019 1. Review of Organic Chemistry I
17/64
17
8/3/2019 1. Review of Organic Chemistry I
18/64
V. Following Electron Flow in Reactions You
Haven't Seen Before
A. Thioester Claisen Condensation
S CH2
O
S CH3
O
+
Note: I will give you either the arrows or the products18
8/3/2019 1. Review of Organic Chemistry I
19/64
continued
S
O -O CH3
S
19
8/3/2019 1. Review of Organic Chemistry I
20/64
A.
B.
20
8/3/2019 1. Review of Organic Chemistry I
21/64
Provide Arrows
HO NH O
-O
H HHO
H N
Provide mechanistic arrows, indicating the direction of electron flow, for the following one-step
transformation. Hint:number your carbons. Where are bonds broken or formed?
O-
H
OO O-
21
8/3/2019 1. Review of Organic Chemistry I
22/64
NH
NH
CH3
O
H
CO2-
+HN
HN
H
NH+
NH
CH3
O
H
CO2-
NH
NH
CH3
O
H
CO2-
+HN
HN
H
NH+
NH
CH3
O
H
CO2-
Which of these groups of mechanistic arrows
is correct? Why? Electron source? Sink?
8/3/2019 1. Review of Organic Chemistry I
23/64
VI. Nomenclature
Examples:1. isopropanol (2 propanol) 2. cis 3-hexene (Z-hexene)
3. tert-butanol (2,2-dimethylethanol) 4. trans-2-butene (E-butene)
5. n-butylamine (1-butyl amine)
You should be able to write structures from IUPAC or common names
23
8/3/2019 1. Review of Organic Chemistry I
24/64
VII. Thermodynamics and Equilibrium
(1) Gravitational (2) Electrical (3) Chemical
24
8/3/2019 1. Review of Organic Chemistry I
25/64
G = H TH
Free Energy is a Combination of Enthalpy and Entropy
25
IfG < 0, reaction is product-favored
IfG >0, reaction is reactant-favored
IfG < 0, reaction is thermodynamically favorable
(higher to lower energy)
IfG >0, reaction is is thermodynamically unfavorable
(lower to higher energy)
In other words:
8/3/2019 1. Review of Organic Chemistry I
26/64
Example of an Exothermic Reaction. Where does the energy
come from?
Consider the reaction H2(g) + Cl2 (g) --> 2 HCl
26
8/3/2019 1. Review of Organic Chemistry I
27/64
27
8/3/2019 1. Review of Organic Chemistry I
28/64
Estimating Reaction Enthalpy from Bond
EnthalpiesOOH
These molecules are a special kind of isomer of one
another called tautomers (molecules that differ by the
placement of a double bond and a proton).
Enol tautomer Keto tautomer
28
8/3/2019 1. Review of Organic Chemistry I
29/64
C=O C-O:
C=C C-C:
29
8/3/2019 1. Review of Organic Chemistry I
30/64
Bonds formed:
Enthalpy of reaction:
OOH
Bonds broken:
30
8/3/2019 1. Review of Organic Chemistry I
31/64
31
Practice: Predicting Entropy Changes
1. CO2 (s) ----> CO2 (g)2. 2CO + O2 (g) ----> 2 CO2 (g)3. Ag+(aq) + Cl-(aq) ----> AgCl (s)4. CO2 (g) ---> CO2 (aq)5.
+ H2
8/3/2019 1. Review of Organic Chemistry I
32/64
Chemical Equilibrium
Concentrations of products and reactants at equilibrium are
CONSTANT.
Equilibrium is DYNAMIC; the rates of the forward andreverse reactions are equal.
Equilibrium concentrations are independent of the direction
of approach (same reaction, same temp).32
8/3/2019 1. Review of Organic Chemistry I
33/64
8/3/2019 1. Review of Organic Chemistry I
34/64
Direction of Approach Doesnt Matter
Figure 14.1
34
N2(g) + 3H2 (g) 2NH3(g)
8/3/2019 1. Review of Organic Chemistry I
35/64
A brief look at kinetics
The rate of a reaction depends on the concentration ofthe reactant(s) and a constant that is characteristic for
the reaction.
For example, isomerization of butene:
Rateforward = kforward [cis-butene]
Ratereverse = kreverse [trans-butene]
What happens to the concentrations of cis and trans
butene as we approach equilibrium?35
8/3/2019 1. Review of Organic Chemistry I
36/64
How do these rate constants relate to the
equilibrium constant Kc?
At equilibrium, Rateforward = Ratereverse
Thus: kforward [cis-butene]eq = kreverse [trans-butene] eq
Rearranging:
kforward [trans-butene] eq=
kreverse [cis-butene]eq
36
8/3/2019 1. Review of Organic Chemistry I
37/64
Writing Equilibrium Constant Expressions
Only consider substances whose concentrations change asthe reaction occurs.
Should we consider:
A) Pure solidsB) Pure liquidsC) GasesD) Solutes in dilute solutions (the stuff thats dissolved)E) Solvents in dilute solutions
For the reaction
aA + bB cC + dD
Keq = --------------------
37
8/3/2019 1. Review of Organic Chemistry I
38/64
Shifting a Chemical Equilibrium: Le
Chateliers Principle
If a system is at equilibrium and conditions are changed so
that the system is no longer at equilibrium, the system will
Example: isomerization of butene. Keq = 1.5 at 600 K
Remove 1/2 of cis butene at equilibrium. What happens?
38
8/3/2019 1. Review of Organic Chemistry I
39/64
Figure 14.6
39
Can drive a reaction to completion by removing one of the
products.
OH
OOH
O
O+ H2O
init. 1 mmol 1 mmol 0 mmol 0mmoleq. .33 mmol .33 mmol .67 mmol .67mmol
propyl acetateH2SO4
8/3/2019 1. Review of Organic Chemistry I
40/64
40
The concentrations of reactants and products at equilibrium are
dictated by the difference in free energy between them:
At room temperature,
For example calculate Keq
for following reaction:
N2(g) + 3H2 (g) 2NH3(g)
G =-32.90 kJ
Or to estimate, Keq =
8/3/2019 1. Review of Organic Chemistry I
41/64
A word about arrows
41
Irreversible Reactions:
Reversible Reactions:
Note: your book uses equilibrium arrows only when the reaction is actually at
equilibrium. This is technically correct but not very useful pedagogically. We will usereversible arrows to indicate that both forward and reverse reactions are occurring.
OH
O Oheat O
+ CO2 (g)
OH
O
OHO
O + H2O
H2SO
4 Keq = 4
OH
OH
NH3OH
O NH4 Keq ~ 1016
8/3/2019 1. Review of Organic Chemistry I
42/64
VIII. Acid-Base Reactions and pKas
Normally written in simplified form:
Ka =[HA]
[H3O+ ][A- ]
H-A + H2O H3O+ + A-
Or
Ka is simply the equilibrium constant for this reaction:
H+
+ A-H-A H+ + AH-A
+
42
8/3/2019 1. Review of Organic Chemistry I
43/64
Arrow pushing for acid-base reactions:
43
Why is this wrong?
8/3/2019 1. Review of Organic Chemistry I
44/64
Directionality of Acid-Base Reactions
44
In which direction does the equilibrium lie?
?
8/3/2019 1. Review of Organic Chemistry I
45/64
Which is the stronger acid, HA or HB?
Stronger base?
8/3/2019 1. Review of Organic Chemistry I
46/64
Acidity and pKa
Ka =[H-A]
[H+ ][A- ]
So, the higher the Ka, the stronger or weaker the acid?
So, the higher the pKa, the stronger or weaker the acid?
If the pKa values differ by 1 unit, by how much do Kas differ?
Define pKa:
If Ka = 10-7, what is pKa?
7
46
8/3/2019 1. Review of Organic Chemistry I
47/64
Acid-Base Equilibria
In which direction doesthe equilibrium lie?
Is Keq < 1 or > 1?
Keq=
47
8/3/2019 1. Review of Organic Chemistry I
48/64
Where K = Ka
8/3/2019 1. Review of Organic Chemistry I
49/64
Acid Conjugate Base pKa Ka
H-Cl
OH
O
acetic acid
H O H
NH3+
NH4+
O
NH2
Review from Organic Chemistry I
Note:
Ka =[H-A]
[H+ ][A- ]
49
8/3/2019 1. Review of Organic Chemistry I
50/64
50
8/3/2019 1. Review of Organic Chemistry I
51/64
C C HH H C N:
NH3
H2O HF
Structure and Acidity
Conj base?
pKa?
Conj base?
pKa?
38 16 3
25 9
8/3/2019 1. Review of Organic Chemistry I
52/64
How about within a column of the periodic table?
H-I
H-Br
H-Cl
H-F
CH3OH
CH3SH
8/3/2019 1. Review of Organic Chemistry I
53/64
53
O
OH OH
4.8 15.9
OH OH
v.
10 15
8/3/2019 1. Review of Organic Chemistry I
54/64
What about this series?
54
HH
H
H
H
H
H3C CH3
8/3/2019 1. Review of Organic Chemistry I
55/64
OH
O
OH
O
IOH
O
BrOH
O
Cl
name?
pKa 4.8 3.2 2.9 2.6As halogenelectronegativity
increases,pKa_____________
OH
O
OH
O
ClOH
O
ClOH
O
Cl
pKa 4.8 2.9 1.5 0.7
Cl ClCl
Inductive Effects
8/3/2019 1. Review of Organic Chemistry I
56/64
OH
O
_________
4.8
ClOH
O
______________
4.5
OH
O
_________
4.0
OH
O
______________
2.8
Cl
Cl
Inductive effect falls off rapidly with distance:
Example 16.2. Pick the stronger acid in each pair.
OH
O
OH
Ov.
name?
8/3/2019 1. Review of Organic Chemistry I
57/64
57
OH OH
NO2
OH
NO2
10 8.4 7.2
Explain:
8/3/2019 1. Review of Organic Chemistry I
58/64
58
OO
Which is the most acidic proton in thismolecule? Next? Least?
When the acid is neutral, consider the stability of the conjugate base.
The more stable (less reactive) the conjugate base, the more reactive the acid,
lower pKa.
8/3/2019 1. Review of Organic Chemistry I
59/64
How to decide which atom is most basic?
59
Draw resonance structures for each form:
8/3/2019 1. Review of Organic Chemistry I
60/64
OCH3
O
OCH3
O H
acid conjugate base
NH2
O
NH2
OH
pKa
-6.5
-0.5
Why is the protonated estermore acidic than the
protonated amide?
Hint: think about resonance
structures.
60
8/3/2019 1. Review of Organic Chemistry I
61/64
List the five structural factors important for
determining the pKa of an acid:
61
1)
2)
3)
4)
5)
8/3/2019 1. Review of Organic Chemistry I
62/64
IX. pKas and Substitution Reactions
A. Which molecule is more likely to react via an SN2
mechanism? SN1? Predict products?
62
8/3/2019 1. Review of Organic Chemistry I
63/64
63
8/3/2019 1. Review of Organic Chemistry I
64/64
64