2015 Chemistry 143 NMR Spectroscopy Problem Set #2 Due Friday April 17, 2015
ppm
multiplicity, J values (Hz)
Problem 1. Tabulate the 1H
CH3COO
Ha 6.46
NMR (500 MHz, CDCl3)
Hb 5.33
information and assign the
Hc 5.22
protons and coupling
CH3COO
Hd 4.84
constants to the structure.
O
He 4.39
Hf 4.25
CH3COO
Hg 4.19
Problem 2 (a) Choose the correct structure of C10H14O3 from the 1H NMR (500 MHz, CDCl3)
spectrum provided. For each of the other structures, indicate one reason why it is incorrect.
CH3
CH3
O
O
O
O
O
CH3
CH3
O
O
O
O
CH3
O
O
CH3
CH3
O
CH3
O
O
CH3
O
O
CH3
CH3
O
CH3
O
(b) Explain the origin of the four proton multiplet found near 2.8 ppm and assign each
individual proton to a carefully drawn structure which you have chosen.
Hj
CH3
CH3
H
O
H
OCH2OCH3
Problem 3. Assign the
protons Ha to Hi to the
structure and calculate the J
values for the multiplet at
2.16
ppm.
(1101.88,
1098.66, 1094.71, 1090.87,
1087.28, 1083.28, 1079.62,
1075.74, 1071.70, 1068.59)
a 5.90 (dd, 1H, J = 1.4, 2.3 Hz)
b 4.99 (dd, 1H, J = 1.4, 2.6 Hz)
c 4.71 (d, 1H, J = 6.7 Hz)
d 4.64 (d, 1H, J = 6.7 Hz)
e 4.24 (ddd, 1H, J = 3.4, 7.2, 8.7 Hz)
f 3.38 (s, 3H)
g 2.68 (dq, 1H, J = 2.1, 11.9 Hz)
h 2.57 (ddd, 1H, J = 2.8, 8.8, 18.8 Hz)
i 2.46 (dt, 1H, J = 8.7, 18.8 Hz)
Problem 4. Below is shown the 1H NMR (500 MHz, CDCl3) spectrum of a single dimethyl
diphenylcyclobutanedicarboxylate isomer Ph2(CH)4(CO2Me)2. When this isomer 1 is treated with
NaOMe/MeOH to allow ester isomerization, it is converted to a different isomer 2 1H NMR (500
MHz, CDCl3) and 13C NMR (75 MHz, CDCl3). From the possible structures shown, choose the
correct structures of 1 and 2.
Ph
Ph2
(CO2Me)2
NaOMe
Ph2
MeOH
1
2
(CO2Me)2
MeOCO
Ph
MeOCO
CO2Me
Ph
MeOCO
CO2Me
Ph
Ph
Ph
MeOCO
CO2Me Ph
CO2Me
Ph
Ph
CO2Me
CO2Me Ph
CO2Me
Ph
CO2Me
Ph
Problem 5. Propose a structure for the ester C8H12O2. 1H NMR (300 MHz, CDCl3) and 13C
NMR (75 MHz, CDCl3):
Problem 6. Grushin and coworkers have prepared an organometallic cluster by treating
Ph(PPh3)PdOH dimer with CpCr(CO)3H at room temperature (Organometallics 1997, 16, 97).
H
O
Ph
Pd
Ph3P
Ph
Pd
O
H
PPh3
+ OC
-H2O
Cr
OC H
O
C
CO
Ph
Ph3P
Pd
Cr
O
C
C
Pd Ph
O O
PPh3
H
The 1H decoupled 13C (75 MHz) spectrum of this complex
shows a triplet at 243.2 ppm and a more complex pattern at
244.6 ppm (as shown below). The 1H decoupled 31P spectrum
of this molecule shows a singlet at 18.0 ppm.
(a) Draw the isotopic species responsible for the complex signal
in the 13C spectrum.
(b) If the phosphorus atoms are participating in this
phenomenon, why does the 31P spectrum only show a singlet?
(c) The simulated spectrum shown above was obtained by using
JPP = +5 Hz and 3JCP = +5 Hz. Using the ABX excel
spreadsheet calculator used in class, test these two values with
2JCP = +19 Hz and then using 2JCP = -19 Hz. What is the most
reasonable choice for Δν for this system? Which choice
reproduces the simulated spectrum from the publication?