Substituents Located on Both Rings

SM was obtained by Friedel-Crafts acylation of 2,3-dichloroanisole with 3,4-dichlo-robenzoyl chloride in the presence of aluminium chloride in refluxing methylene chloride [475] or in ethylene dichloride at 60° for 1 h [476]. m.p. 179-180° [476] Spectra (NA). 

Q - Preparation by Fries rearrangementof 3,5-dichlo- rophenyl 2,5-dichlorobenzoate with aluminium 

5-dichlorophenyl 3,4-dichlorobenzoate with alnmininm chloride first 10 min at 140-150°, then for 30 min at 150-160° (80%) [458]. 

5-dichlorophenyl 2,4-dichlorobenzoate with alnmininm chloride in chloro-benzene for 20 min at 140-150° or in nitrobenzene for 24 h at 75° [480]. 

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Substituents Located on Both Rings [1476] p. 409 (3,4-Dihydroxy-5-nitrophenyl)(2-fluorophenyl)methanone... 

Photochromic reactions of cw-l,2-diarylethenes are the extension of photochemical electrocyclization of cw-stilbene, which yields dihydrophenanthrene. When the aromatic stabilization energy (aromaticity) of at least one aryl group is low (such as furan, thiophene, benzothiophene) and the nonhydrogen substituents are located on the ring-forming carbon atoms, the thermally irreversible photochromism is observed. When the aromaticity of both aryl groups are high (such as phenyl, indolyl, or pyrryl), the diarylethene is thermally reversible [31]. 

These data on the hydrogen exchange in the alkyl groups of arenium ions and their precursors cover the examples when both substituents located at the ring sp -hybridized carbon are not hydrogen. A similar exchange scheme, however, is also possible for ions formed upon protonation of alkyl-substituted aromatic compounds. 

Fit of (R) and (S) 8-OH-DPAT according to a) Hibert et al. [34] and b) Mellin et al. [35], In both fits the nitrogen lone pairs coincide. In a) the hydroxy groups are also fitted, but not the aromatic centers. In contrast, in b) the aromatic centers are fitted, while the hydroxy groups are located on opposite sides of the benzene ring. As a result, in a) the N-substituents of both enantiomers are more distant than in b). 

Following the dipole moments presented, quaternary alkylations on nitrogen take place readily. But unlike pyridine, both quinoline and isoquinoline heterocyclic nitrogen promote the reaction with nucleophiles. What is more, electrophilic substitution takes place much more easily than in pyridine, and the substituents are generally located in carbocyclic ring preferentially in the more activated positions of the benzene ring, with a positional selectivity in the case of quinolines in the order of C8 > C5 > other positions. 

In the previous examples it was possible to discuss the effect of a substituent only in terms of the induction/field effect or primarily in terms of the resonance effect. Both effects are important for many substituents, and the location of the substituent on the ring influences how the effects influence the reaction site. The positive value for the methoxy group indicates that it... 

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