HW 2 Multinuclear NMR Name:
Points: C6800 Date:
Max. 100 points Spring 2011 Version A
1. Predict the number and relative intensity of the signals in the 29
Si NMR spectra of
molecules 1–3. For 1 and 3 give the symmetry point groups.
2. Gold(I) tris(ethylene) complex [Au(C2H4)3][SbF6] was prepared by the following reaction
and was structurally characterized.
a) Draw clearly all symmetry elements present in the cation.
b) Give the symmetry point groups of the cation and the anion.
c) Is this complex diamagnetic or paramagnetic?
d) How many resonances (signals) do you expect in the 1
H and 13
C NMR spectra.
e) These resonances are significantly upfield relative to the free ethylene (5.28 / 123.2 ppm).
What causes this shielding effect?
Δδ(13
C) = δ(13
C)complex − δ(13
C)ethylene
[Ag(C2H4)3] [Al{OC(CF3)3}4] −7.0 ppm
[Au(C2H4)3][SbF6] −30.7 ppm
f) What are the 13
C NMR chemical shifts of the two complexes?
3. Alkyl gallium peroxide anion was synthesized by the following procedure:
a) Draw clearly all symmetry elements present in the anion.
b) Give the symmetry point group of the anion.
c) Are there any geminal groups? Assign them as Homo-, enantio-, or diastereotopic.
d) How many resonances (signals) do you expect in the 1
H, 13
C, and 29
Si NMR spectra.
4. How many signals of the NMe2 and CH2 groups do you expect in the following
compounds:
5. How many signals do you expect in 19
F a 31
P NMR spectra of the following compound:
O
PN
O
O
P
P
O
O
F
F
F
F