Disubstituted Rings

FIGURE 5.58 The planes of symmetry present in (a) a para-disubstituted benzene ring (anethole) and (b) a symmetric orf/io-disubstituted benzene ring. 

290 Nuclear Magnetic Resonance Spectroscopy Part Three Spin-Spin Coupling 

FIGURE 5.59 The aromatic ring portions of the 300-MHz H NMR spectra of (a) anethole and (b) 4-allyloxyanisole. 

We will leave the analysis of this second-order pattern to more advanced texts. Note, however, that a crude four-line spectrum is characteristic of a para-disubstituted ring. It is also characteristic 

FIGURE 5.60 The expanded para-disubstituted benzene AA BB pattern. 

Of the possible substitution patterns of a benzene ring, only a few are easily recognized. One of these is the para-disubstituted benzene ring. Examine anethole (Fig. 5.43a) as a first example. 

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In addihon to this so-called 1,3-interaction between an exocyclic substituent and the hydrogens in 3-position, steric interactions can cause extra strain also in 1,2-disubstituted rings as the tra s-l,2-dimethyl-cyclohexane in Fig. 7.10(c). The... 

In Part II we discussed conformational isomerism of disubstituted ring systems from the standpoint of nonbonded interactions. Here, we shall examine the importance of a—a conjugation in these molecules. 

Disubstituted rings crystallize in a chair conformation (see Fig. 18). The molecules contain three-dimensional Fl-F bridges. The rings are perpendicular to each other.61... 

Answer Since IX-f contains a disubstituted ring with each substituent containing carbon atoms, yes, we do have to add carbon atoms. 

Answer Yes, because X-b is a disubstituted ring and each substituent contains carbon atoms, > ... 

The amphibian quinolizidines appear to be 1,4-disubstituted ring homologs of the 5,8-disubstituted indolizidines. A characteristic Bohlmann band pattern in their FTIR spectra, which is broader and less intense than that... 

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