HW 2 Multinuclear NMR Name:
Points: C6800 Date:
Max. 100 points Spring 2018 Version A
1. (3 pts) The 119
Sn NMR resonance of the Sn atom at the apex of the square pyramid in 3 was found to
be extraordinarily shielded, being observed at −2441.5 ppm. The value closely approaches those of the
stannocene derivatives, with their record high-field tin resonances appearing in the range from −2100 to
−2300 ppm. Explain these observations considering the two resonance structures of pyramidane 3,
covalent and ionic. Which one is more important?
2. (15 pts) Mark geminal protons of CH2 in the following molecule as homotopic (H), enantiotopic (E)
and diastereotopic (D). Find the symmetry point group of each molecule:
3. (4 pts) Explain the 19
F {1
H} NMR spectrum the following molecule, mark all peaks, spin interaction
constants and give relative intensities:
4. (38 pts) Draw schematically all possible complexes [PFx(CN)6-x] (x = 0 – 6) and give the label of the
corresponding point group. Predict multiplicities of signals in 31
P and 19
F NMR spectra (number of
resonances, name of a multiplet, and the relative intensities of lines in a multiplet).
x Molecule
Point group
31
P 19
F
6
5
4
3
2
1
0
5. (6 pts) Calculate relative populations of 207
Pb isotopologues in the molecule of plumbane:
H3C
Pb
H3C
H3C
C C Pb
CH3
CH3
CH3
6. (4 pts) Values of interaction constants in following anions recalculate for other NMR active isotopes
of Ga, In and Tl.
[GaF6]3 1
J(71
Ga-F) = 245.4 Hz
[Ga(CF3)4] 2
J(71
Ga-F) = 150.2 Hz
[InF6]3 1
J(115
In-F) = 420.0 Hz
[Tl(CF3)4] 2
J(205
Tl-F) = 2072 Hz
7. (4 pts) Explain differences between values of interaction constants:
Si O
P
O
F
F Si O
P
O
F
F
JPF = 974 Hz JPF = 967 Hz
Me3Si O
P
O
F
Cl
JPF = 1064 Hz
Me3Si O
P
O
F
Cl
JPF = 1095 Hz
BCl3
8. (26 pts) Classify spin systems (magnetic in/equivalence) in proton NMR spectra of following
molecules. Give both prime and bracket notation labels:
Prime Bracket Prime Bracket
A H
B I
C J
D K
E L
F M
G