HW 4 Multinuclear NMR Name:
Points: C6800 Date:
Max. 100 points Spring 2014 Version A
1. Fluorinated ethers are used as anestethics.
a) (10 pts) Give number of signals, integral intensities, splitting patterns (multiplicity) and
relative intensities of lines in the multiplets (consider only 1
H and 19
F and maximum threebond
scalar coupling).
b) (10 pts) In compounds B to D find and classify the geminal groups (H, E, D).
A) Isoflurane CF3CHClOCHF2
B) Desflurane CF3CHFOCHF2
C) Enflurane CHClFCF2OCHF2
D) Sevoflurane (CF3)3CHOCH2F
2. (12 pts) Find all possible coupling constants and write a proper label n
JAB for each of them.
Consider only 31
P and 19
F nuclei:
3. (8 pts) Photolysis of HSiCl3 provides a compound with an empirical formula Si5Cl12. The
product displays two chemical shifts in the 29
Si NMR spectra in a 4:1 intensity ratio. Derive
structural formula of this molecule.
4. The 13
C{1
H} NMR spectrum in the picture belongs to Li[Al(CH3)4] in dimethoxyethane.
a) (10 pts) Explain multiplicity of the signal, intensities of lines in the multiplet, and mark a
coupling constant in the spectrum.
b) (5 pts) Which property of this molecule allows observing the splitting? Give the symmetry
point group.
c) (5 pts) How would this spectrum change after turning off decoupling.
5. Consider NMR spectra of the anion Tl3Se7
5(its
symmetry point group is C3v) in liquid
NH3, at 68 °C:
a) (10 pts) Calculate abundances of isotopomers of Tl (disregard Se nuclei).
b) (10 pts) Consider the following isotopomer (enriched to 100% both in Se = 77
Se, and Tl =
205
Tl):
Designate this spin system by prime and bracket notations:
6. (10 pts) Draw 31
P{1
H} NMR spectrum of following compound, consider maximum twobond
scalar couplings with isotopes in natural abundance, mark the coupling constants in the
spectrum:
7. (10 pts) Calculate abundances of isotopomers (77
Se) in the following cyclic molecule.
(Hint: Abundance for the whole molecule in a product () of abundance for site A and
abundance for site B):