Exam #2, October 24, 2008.
MU, Chemistry 8160, FS08, Dr. Glaser
Your Name:________________________________________________________________________________
Question 1. NMR Basics. (26 points)
(a) Indicate schematically the magnetic moments of “individual nuclear spins” (draw some 10-15) as arrows for
the following situations. Assume as always that the external magnetic field is pointing straight up (z-direction).
(12 points)
After sample is placed in
magnetic field. (But no
pulses as yet).
After one “90° pulse.”
After one “180° pulse.”
One hour after applying
one “90° pulse.”
(b) Draw a scheme of the Zeeman levels for an
AB-pair of H-nuclei and assume that J(HA,HB) = 0.
(4 points)
(c) Solvents (10 points)
Multiplicity depends on the number of equivalent neighbors n and their nuclear spin I and the multiplicity is
given by __________. For spin I = ½ nuclei, this formula simplifies to the ________-rule.
Acetonitrile-d3 (you observe Acetonitrile-d_)
Acetone-d6 (you observe Acetone-d_)
13
1
C couples to n =___ equivalent ___-atom(s) with
nuclear spin I = _____.
Multiplicity of 13C signal: _______________
H couples to n =___ equivalent ___-atom(s) with
nuclear spin I = ____.
Multiplicity of 1H signal: _________________
-1-
Exam #2, October 24, 2008.
MU, Chemistry 8160, FS08, Dr. Glaser
Your Name:________________________________________________________________________________
Question 2. Chemical Shifts & Increment Systems. (14 points)
1
H- and 13C-NMR of Eugenol
The structure of eugenol is shown and the chemical shift data are taken from the SDBS database. Using the
book by Pretsch et al., find the base value for the chemical shift of an aromatic C-atom “Cx”, locate the Zivalues and provide them in the table below. Do the same for the attached H-atom. Make sure to indicate the “i”
of the Zi-values (where the underline is shown). Then make the additions to obtain the “calculated” chemical
shift, assign the “measured” peaks and enter their chemical shifts in the respective row, and, finally, compute
the difference between “calculated” and “measured” values.
H-NMR Chemical Shifts (ppm)
A: 6.832; B: 6.66; C: 6.65; D:
5.933; E: 5.73; F: 5.058; G:
5.039; J: 3.801; K: 3.291.
HO
H3CO
C-NMR Chemical Shifts (ppm)
146.60, 144.03, 137.91, 131.94,
121.26, 115.49, 114.46, 111.28,
55.84, 39.92.
Cx
Hx
Cx
Hx
Base =
Z (OMe) =
Z (OH) =
Z_(CH2–CH=CH2) =
Base =
Z (OMe) =
Z (OH) =
Z_(CH2–CH=CH2) =
Calculated:
Measured:
Deviation:
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Exam #2, October 24, 2008.
MU, Chemistry 8160, FS08, Dr. Glaser
Your Name:________________________________________________________________________________
Question 3. C6H6O2 (20 points)
NMR and IR spectra are provided for a
molecule with formula C6H6O2. Deduce its
structure and assign the spectra.
1
H-NMR: 399.65 MHz, 0.04 g : 0.5 ml DMSO-d6
13
C-NMR: 22.53 MHz, 0.04 g : 0.5 ml DMSO-d6
-3-
Exam #2, October 24, 2008.
MU, Chemistry 8160, FS08, Dr. Glaser
Your Name:________________________________________________________________________________
Question 4. C14H10 (20 points)
NMR spectra are provided for a hydrocarbon
with formula C14H10. Deduce its structure and
assign the spectra.
1
H-NMR: 89.56 MHz, 0.04 g : 0.5 ml CDCl3
13
-4-
C-NMR: 15.09 MHz, 0.198 g : 0.8 ml CDCl3
Exam #2, October 24, 2008.
MU, Chemistry 8160, FS08, Dr. Glaser
Your Name:________________________________________________________________________________
Question 5. Butanol. (20 points)
NMR spectra are provided for the alcohol with
formula C4H10O, 2-Butanol.
-- Draw its structure, mark each chiral center,
and mark each H-atom (or group of equivalent
H-atoms) as homotopic, enantiotopic, or
diastereotopic.
-- How many signals do you expect if one pure
stereoisomer is present?
-- Do the spectra show one pure stereoisomer?
1
H-NMR
13
-5-
C-NMR