Peri effect

The relations in Scheme V take into account intranuclear and intemuclear resonance activation and the special cases of 2-Le-3-aza (poor) and 4-Le-8-aza (extremely poor) activation as well as the two groups of inductive activation the possibility of an accelerative peri effect in substitutions with protic nucleophiles is indicated by the sign for 4-Le-5-aza compounds. 

The author17 explains the difference by involvong the peri-effect in 1,8-dihydroxynaphthalene. 

Some quinone methides with two MeS groups or one MeS and one Me2N group as donors (47b, 48 to 50) show quite low barriers (49). In the naphthoquinone methides a ground state destabilizing peri effect must be at work, but... 

The results of nitration reactions depend on reagents and the acidity of the medium. Thus fuming nitric acid in concentrated sulfuric acid converts (410a) to the 3-nitro derivative while with acetyl nitrate reaction occurs exclusively at C-4 (equation 50). The nitration in the 4-position can also conveniently be done with nitronium tetrafluoroborate. The reduction of these nitro compounds by hydrazine in the presence of palladium on charcoal provides a versatile route to 4-amino-7,6-borazarothieno[3,2-c]pyridines (75ACS(B)46l>. In the nitration of 4,5-borazarothieno[2,3-c]pyridines (e.g. 409a), peri effects from the substituents on the boron atom lead to formation of a considerable amount of the 2-nitro derivatives. 

P. G. Seybold and K. B. Lipkowitz, Int. J. Quantum Chem., 31, 847 (1987). An Empirical Force Field Examination of the peri Effect in Aromatic Hydrocarbon Carcinogenesis. 

The mass spectra of several thiete sulfones have been interpreted on the basis of ring-opening to the cyclic sulfinate (sultine). Benzothiete sulfones lose sulfur dioxide to give benzocyclopropenium ions. The peri effect in 1,8-disubsti-tuted naphthalene derivatives, for example, 205b, has been discussed. ... 

Peri effects of azine-nitrogens and of nitro groups are indicated by the data in Section IV, A, 2. For reaction in piperidine solution, the rates of peri or 1,8-situations of the leaving group and inductive-activating center are anomalously higher than those of the isomeric... 

Le-4-aza = 4-Le-2-aza g 4-Le-5-aza(internuclear) all equidistant accelerative peri effects in 4-Le-5-aza compounds occur in some reactions ... 

The thermochemical database for substituted naphthalenes is far less extensive than for substituted benzenes and is reproduced in Table 5. For a given R, there are two isomeric monosubstituted naphthalenes, the 1-R and the 2-R. The latter might be expected to be more stable because it lacks the 1.8-or peri-repulsion found in the former between the substituent and a small, but unavoidably nearby, hydrogen. For a methyl substituent, the difference between the enthalpies of formation of 1- and 2-me-thylnaphthalene, 113.5 1.7 and 110.7 1.7 kJ/mol, respectively, reveals a very small 2.8 2.4 kJ/mol peri effect. For identical substituents, there are the following naphthalene isomers 1.2-. 1.3-. 1.4-. 1,5-, 1.6-. 1.7-. 1.8-, 2,3-, 2.6-. and 2.7-isomers. There is no substituent for which all 10 isomers have been thermochemically characterized. Furthermore, there is only one substituent for which there are enthalpy of formation data for the isomer of greatest interest— 1,8-dimethylnaphthalene. Equation 20. analogous to eq 18, is now recast for mono- and disubstituted naphthalenes ... 

It is of interest that 9-ethyl and 9-isopropylanthracene do not show the same large deviation from the correlation for ring substitution. The simplest conclusion is that exocyclic hydrogen abstraction is less likely here because of peri effects caused by replacing one or both of the methylene hydrogens by methyl groips. 

Certain distinct conclusions may be drawn from these studies. Firstly, as might have been expected, is the obvious fact that delocalization can have a tremendous effect on the ease of benzylic radical formation. The peri effects, invoked by earlier mechanicians, seem to be less important than claimed for non-substituted systems, but, may exert a large effect if substituents are attached to either the exocyclic atom or the peri site. (Although only rate retarding peri effects have been treated above, accelerative counterparts can be easily imagined.) Finally, from the theoretical point of view, all of the work on formation of benzylic like radicals cited enforce the view that calculations which do not include interelectron terms are inadequate and that ground state parameters cannot successfully... 

OXO-, see azines, hydrosy-perfaaloallgd-, reactions of, 230 peri effects, 311,361 phenylazo-, reactions of, 241 phosphorylosy-, reactions of, 210 poly-, covalent addition to, 362 positional reactivity of, 172-174, 177-181, 264, 361 quatemization of, 161 quartemization, effect on reactivity, 308... 

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