Name: _________________________________
CHEM 332. Midterm 2
Spring 2015
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 10 pages in this exam. Please check that your test has 10 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 / Jennie
Tues / Andrew
Wed / Jennie
Thurs / Andrew
Question
Points
1
_____ /20
2
_____ /15
3
_____ /25
4
_____ /20
5
_____ /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. (20 points) (a) Please complete the reaction coordinate diagram below for the formation of enolates
2 and 3 from 1.
OK
O
t-BuOK/t-BuOH
CH3
OK
t-BuOK/t-BuOH
CH3
1
2
3
E
O
CH3
+ t-BuOK
reaction coordinate to 2
reaction coodinate to 3
(b) Please explain the relative energies of enolates 2 and 3. Is one more stable than the other? Why?
3
Name: _________________________________
(1 – continued)
(c) Please explain the relative transition state energies for the formation of enolates 2 and 3. Is one
transition state more stable than the other? Why?
4
Name: _________________________________
2. (15 points) (a) Please give the product of the following transformation. Be sure that your structure
is consistent with the 1H NMR spectrum provided.
Br
O
H3C
O
NO2
CH3
Et3N
1
H NMR (300 MHz, CDCl3) δ 2.05 (s, 6H), 3.76 (s, 2H), 7.31 (d, 2H, J =
8.1 Hz), 8.17 (d, 2H, J = 8.8 Hz), 16.84–16.86 (br s, 1H)
(b) Please draw a reasonable arrow-pushing mechanism for the reaction in part (a).
5
Name: _________________________________
3. (25 points) Please draw the major product for each of the following reactions.
1) LiAlH4 (excess)
2) H3O+
O
(a)
O
1)
N C N
O
(b)
H2N
OH
2) K2CO3,
CH3
1) CrO3, pyridine
2) cat. HCl,
HN
Me
(c)
Me
(d)
OH
3) MeI; then H3O+
O
NaOH, H2O
H
O
(e)
Br
1) LiN(i-Pr)2, –78 °C
2) Me3SiCl
6
Name: _________________________________
4. (20 points) Please draw a reasonable arrow-pushing mechanism for the following reaction.
Hint: The reactivity of ethyl nitrite (1) is analogous to the reactivity of an ester.
H
Ac
+
N
H
O
CH3
O N OEt
1) NaOEt
2) H3O+ (work-up)
OEt
Ac
1
O
H
N
NOH
H
CH3
7
Name: _________________________________
5. (20 points) Provide a synthesis of n-propanol from i-propanol. You may use any inorganic reagents
and any organic reagents with less than 2 carbons.
OH
H3C
CH3
i-propanol
H3C
OH
n-propanol
8
Name: _________________________________
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Name: _________________________________
This page was intentionally left blank and may be used for scratch paper.
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