Coupling Constants Identify Coupled Protons

Predict the splitting patterns for the signals given by compounds a-m in Problem 4. 

Identify the following compounds. (Relative integrals are given from left to right across the spectrum.) 

Describe the NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals  

The a and b protons of 1,1-dichloroethane are coupled protons— that is, they split each others signals, so their signals have the same coupling constant. Jot, = -fba- 

The doublets observed for the a and b protons in the H NMR spectra of a trans alkene and a cis alkene. The coupling constant for trans protons (14 Hz) is greater than the coupling constant for cis protons (9 Hz) because it depends on the dihedral angle (180° for trans protons 0° for cis protons). 

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The multiplets and coupling constants of the axial) protons at = 3.15, 3.50 and 4.08 moreover confirm the equatorial positions of all three OH groups, as can be seen in formula B. Here the couplings from 10.0 to 11.5 Hz, respectively, identify vicinal protons in diaxial configurations, whilst values of 4.5 and 5.0 Hz, respectively, are typical for axial-equatorial relationships. As the multiplets show, the protons at 5 = 3.50 and 4.08 couple with two axial and one equatorial proton (triplet of doublets) respectively, whereas the proton at = 3.15 couples with one axial and one equatorial proton (doublet of doublets). 

Fattorusso and co-workers identified a component of wormwood called artar-borol. Correlation spectroscopy (COSY) and rotating frame nuclear overhauser effect spectroscopy (ROESY) experiments allowed for deduction of four possible diastereomeric structures of artarborol, 2-5. Low energy conformers of 11-14 were obtained through a molecular mechanics (MM) search. These conformers were screened to identify those having a dihedral angle of around 90 for the C-8 and C-9 protons due to a low coupling constant between these protons. Only conformers of 11 and 13 satisfied this criterion. Next, five low energy conformers, two... 

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