NMR - structural analysis: TEST 2
1. Figure bellow shows 1
H NMR spectrum of Z and E isomer of C2H2Cl2. Hint: Consider non-equivalent
character of H atoms attached to 12C and 13C.
a) By analyzing the splitting of 13C satellites, identify chemical shift of both isomers.
b) Estimate the values of 1JHC and 3JHH.
c) Calculate the optimal delay needed for evolution of anti-phase magnetization in case of
heteronuclear coupling. Draw a vector scheme of INEPT sequence.
2. Attached figure shows standard 1H NMR spectrum of presented bicyclic compound and two inserts
which are difference spectra (subtraction irradiated - standard) resulting from selective irradiation of
signals at either 0.95 or 1.38 ppm.
a) What type of phenomena is used in these experiments?
b) Was decoupler active during acquisition of irradiated spectra?
c) Based on comparison of the individual spectra assign resonances of Ha-Hf. Explain your decision.
1.43 2.08 2.28 2.43 2.55 2.60
d) Comment on chemical shift difference between methyl groups as well as He and Hf.
3. 1H-1H COSY spectrum shown below contains mixture of butylbromid and butanal.
a) Assign the signals of both molecules. Comment on the spitting of signal at 2.4 ppm (look at 1D
projection at the border).
b) Why do crosspeaks differ in splitting between mirror images?
c) Based on crosspeak 1.6, 2.4 try to describe the meaning of “active” and “passive coupling” terms.
4. Try to identify resolved 1H signals of a diterpenoid-lactone based on 1D NMR spectrum and NOESY
correlations.
a) Redraw structure into perspective formula and check number of non-equivalent protons. Denote
examples of diasteretopic atoms.
b) Based on molecular weight and sign of off-diagonal NOE crosspeak suggest approx. mixing time of
recorded NOE experiment. Which cross-relaxation is usually dominant for such type molecules?
c) Explain opposite sign of off-diagonal crosspeak of exchangeable protons and assign them. Hint
Deshielding effect of attached carbon atom increases from primary to tertiary carbon.
f) Use edited 1H-13C HSQC to find some geminal protons. Try to interpret resolved NOE crosspeaks.