Group 2 - Aromatic and Heterocyclic Protons

Protons on aromatic rings are generally fairly predictable, both as regards to their position, and shape. The effects of substituents on a benzene ring are shown in Table 5.4. 

They are applicable to compounds in the common NMR solvents - but not in D6-benzene (or D5-pyridine). The substituent effects are additive, but don t place too much reliance on chemical shifts predicted using the table, in compounds where more than two groups are substituted next to each other, as steric interactions between them can cause large deviations from expected values. Note that Table 5.4, like all others, does not cater for solvent shifts, etc  

A number of features become apparent on running an eye over these figures. Firstly, one saturated carbon in a substituent between the benzene ring and another group (e.g., -CH2-OH) is sufficient to 

Spectrum 5.2 A very broad carboxylic acid signal. 

As for spin coupling around the benzene ring, Table 5.3 shows the expected ranges and typical values. 

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