Splitting diagrams triplet

You will find It revealing to construct a splitting diagram similar to that of Figure 13 20 for the case in which the CIS and trans H—C=C—H coupling con stants are equal Under those circumstances the four line pattern simplifies to a triplet as It should for a proton equally coupled to two vici nal protons... 

If a proton or set of protons is not coupled equally to neighboring protons, then die n + 1 rule is not adequate to describe the multiplicity of die absorption. Instead one observes multiplets of multiplets as the splitting pattern (e.g., doublet of doublets or triplet of doublets). The multiplicity can be understood by carrying out sequential splitting diagrams. For example, consider a proton II/, split by two neighboring vicinal protons II and Hc by Jab = 2 Hz and Jbc = 1 Hz. This is... 

A splitting diagram for a quartet of triplets. The number of peaks actually observed when a signal is split by two sets of protons depends on the relative magnitudes of the two coupling constants. 

We expect the signal for the methyl protons adjacent to the diastereotopic hydrogens of 2-bromobutane to be a doublet of doublets as a result of splitting by the nonequivalent diastereotopic hydrogens. The signal, however, is a triplet. Use a splitting diagram to explain why it is a triplet rather than a doublet of doublets. 

Figure 1.2. Jablonski energy level diagram showing the singlet state and the triplet state with its zero-field splittings for a planar aromatic chromophore.

Analogous negative ion PES experiments reveal that the singlet-triplet splitting of methylene (CH2) is only 9.05 kcal/mol.This difference is easily understood on the basis of a simple molecular orbital (MO) diagram. 

Fig. 15. Energy level diagram for a triplet molecule in the absence and presence of a zero-field splitting of the 0 and + 1 levels.

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