Chemical shifts fused aromatic rings

TABLE D.4 Chemical Shifts of Protons on Fused Aromatic Rings... 

Table 3.11 Chemical shifts of protons on fused aromatic rings 7.81 8.31 7.91...

The chemical shift of the angular proton in benzo[c]quinolizidines will differ from that in quinolizidine itself as a result of delocalization of the lone pair electrons over the aromatic ring in certain conformations. Examples are provided by 29 and 30. In trans-fused 29, the nitrogen lone pair is delocalized over the aromatic ring and thus the anti-coplanar shielding mechanism is lost and the angular proton absorbs to low field of that in the cis conformation 30.51... 

Amongst the benz-fused systems, the question of aromaticity in 1,2-benzothiazepine 1,1-dioxides has been addressed by Abramovitch and co-workers. The benzothiazepines are very stable chemically, but the chemical shifts for the H-4 protons in (25b) and (25c) (5 7.1 and d 7.2, respectively), and for the H-5 protons in (25a) and (25c) (d 6.2 and d 6.3), together with the relatively large size of the A 5 coupling constant (12.7 Hz in (25c)), indicates that the seven-membered ring is not aromatic, favoring structure (25) over (26) (Equation (1))) <83CC520>. 

The n.m.r. spectra of a series of benzocycloalkanes and their 3- and 4-fluoro-derivatives have been obtained, including benzycyclobutane." Aromatic carbon assignments were confirmed, in the case of the hydrocarbons, by use of appropriately deuteriated substrates. The variation of the chemical shifts with the size of the fused ring has been discussed. The n.m.r. spectra of these compounds were also examined,... 

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