Name: _________________________________
CHEM 332. Midterm 2
Spring 2016
Prof Mary Watson
Please write your answers clearly in the boxes provided. If your answer is illegible or
outside the box, it will not be graded. You may use the back of test pages for scratch
work.
You may use molecular models.
Use of calculators, cell phones, headphones, or any other electronic device during this
exam is prohibited.
No notes or books may be used during this exam.
You may raise your hand to ask a question if you are not sure what is being asked of
you.
There are 11 pages in this exam. Please check that your test has 11 pages before you
begin. The last 2 pages are blank and may be used as scratch paper. Page 2 contains
potentially useful IR and NMR spectral tables, as well as a periodic table.
Please circle your discussion
section:
Mon
Tues
Fri
Question
Points
1
_____ /12
2
_____ /8
3
_____ /20
4
_____ /20
5
_____ /20
6
_____ /20
Total
_____ /100
1
Name: _________________________________
Approximate IR Absorption Frequencies
Bond
O–H (alcohol)
O–H (carboxylic acid)
N–H
C–H
C≡N
C≡C
C=O
C–O
1
Approximate H NMR Chemical Shifts
Hydrogen
δ (ppm)
CH3
0.8–1.0
CH2
1.2–1.5
CH
1.4–1.7
C=C–CHx
1.7–2.3
O=C–CHx
2.0–2.7
Ph–CHx
2.3–3.0
2.5
≡C–H
R2N–CHx
2.0–2.7
I–CHx
3.2
Br–CHx
3.4
Cl–CHx
3.5
F–CHx
4.4
O–CHx
3.2–3.8
C=CH
4.5–7.5
Ar–H
6.8–8.5
O=CH
9.0–10.0
ROH
1.0–5.5
ArOH
4.0–12.0
RNHx
0.5–5.0
CONHx
5.0–10.0
RCOOH
10–13
–1
Frequency (cm )
3650–3200
3300–2500
3500–3300
3300–2700
2260–2220
2260–2100
1780–1650
1250–1050
Intensity
Strong, broad
Strong, very broad
Medium, broad
Medium
Medium
Medium to weak
Strong
Strong
13
Approximate C NMR Chemical Shifts
Carbon
δ (ppm)
Alkanes
Methyl
0–30
Methylene
15–55
Methine
25–55
Quaternary
30–40
Alkenes
C=C
80–145
Alkynes
70–90
C≡C
Aromatics
110–170
Benzene
128.7
Alcohols, Ethers
C–O
50–90
Amines
C–N
40–60
Halogens
C–F
70–80
C–Cl
25–50
C–Br
10–40
C–I
–20–10
Carbonyls, C=O
R2C=O
190–220
RXC=O (X = O or N)
150–180
2
Name: _________________________________
1. (12 points) (a) Two products form in the following reaction. A is favored at low reaction
temperatures. B is favored at high reaction temperatures. Please provide the structures of A and B.
HBr
+
A, major product at low
temperature
B, major product at high
temperature
(b) Please complete the reaction coordinate diagram below to explain your answer to part (a).
E
+ HBr
Reaction coordinate to A
Reaction coordinate to B
3
Name: _________________________________
2. (8 points) (a) Is cyclopropenyl anion aromatic, anti-aromatic, or not aromatic? Please circle your
answer.
Circle one:
aromatic
anti-aromatic
not aromatic
(b) Please draw a molecular orbital diagram for the π system of cyclopropenyl anion to explain your
answer in part (a).
4
Name: _________________________________
3. (20 points) For the following problem, please consider the Diels–Alder reaction shown below.
O
O
X
+
*
Δ
X
H
*
H
*
(a) Please rank the following dienes with respect to their reactivity in this Diels-Alder reaction.
Number the molecules 1–4, giving 1 to the most reactive and 4 to the least reactive.
NH
CH2
O
O
(b) Please show the relative energies of the HOMO’s of the dienes on the molecular orbital energy
diagram below to explain your answer in part (a).
E
CH2
NH
O
O
5
Name: _________________________________
(3 – continued)
(c) Please re-draw the product, showing the stereochemistry at each of the starred carbons (*).
O
*
X
*
H
*
(d) Using clearly drawn structures, please explain your prediction in part (c).
6
Name: _________________________________
4. (20 points) Please draw the major product for each of the following reactions. Please show
stereochemistry where appropriate.
cat. HCl
OH
O
HO
HO
H3C
OH
OH
OH
OH
O
HO
HO
1. HNO3
2. DCC, HNEt2
OH
OH
O
O
O
1. K2CO3, EtO
OEt
Br
NH
O
2. K2CO3, Br
3. HCl, H2O
1. HNO3, H2SO4
2. NaOCH3
Br
CN
OEt
Δ
7
Name: _________________________________
5. (20 points) Please draw a reasonable arrow-pushing mechanism for the following reaction.
O
HO S CF3
O
O
N
Cl
O
Cl
N
H
O
HO S CF3
O
triflic acid
very strong acid
pKa ~ –12
8
Name: _________________________________
6. (20 points) Provide a synthesis of 1 from benzene. You may use any other reagents you want.
CH3
H
N
H3C
O
O
1
9
Name: _________________________________
This page was intentionally left blank and may be used for scratch paper.
10
Name: _________________________________
This page was intentionally left blank and may be used for scratch paper.
11