Peri-substitution

The methodology is useful for a variety of synthetic purposes. The cycloadditions are not subject to steric hindrance. Thus diyne cycloadditions to 2,5-disubstituted furans or pyrroles, followed by elimination of the oxygen or nitrogen bridges, provides an excellent, short route to peri-substituted arenes, as in the following examples 4 6 8... 

Similar statements for IP(tt4) can be made for the two diaminonaphthalenes (15,16). Peri-substituted naphthalenes are examples of molecules with strong intramolecular crowding which can result in unique physicochemical properties. 1,8-Bis(dimethylamino)naphthalene (19) ( proton sponge 88,89) has been found to have an... 

Close examination of the population ratios of the peri substituted compounds (Table 21) shows another point. That is, whereas the sc form of the methoxycarbonyl compound is less favored relative to that of the cyano compound when the peri substituent is methyl, the situation is reversed when the peri substituent is chlorine. Weak attractive interactions between a carbonyl moiety and a peri substituent bearing a lone pair of electrons are known in triptycene systems, and the methoxycarbonyl group is a stronger electron acceptor than cyano (148). This attractive interaction may be the cause for the seemingly anomalous populations. 

Studying further the 1,5-interactions in peri-substituted naphthalenes (which culminated in the complete formation of a single bond in zwitterion 63 (Section 8.11.3.1.1) the corresponding methylthio derivative 242 was investigated <2006CEJ7724> also in this case the MeS sp -C attractive interaction controls the solid state structure of compound 242. 

TMS derivatives, respectively, without the formation of peri-substituted products, as observed in the corresponding naphthalene systems. 6- and... 

One of the most common uses for peri-substituted pentacene is as a red emitter in organic light-emitting diodes (OLEDs). Diphenylpentacene, for example, has a fluorescence quantum yield of 30% as a 0.55% dopant in Alq3, yielding OLED devices with efficiencies near the theoretical maximum [34]. Variation of the aryl substituents improves solubility and processing and can increase fluorescence quantum yield (for example, pentacene 25 has a composite fluorescence quantum yield of 32%) [35]. There is one report of the use of diaryl pentacenes in FET devices, but the performance was generally poor (hole mobility for vapor-deposited 23 was of the order of 10-8 cm2 V-1 s-1) [30]. 

Scheme 6. Regioselective cleavage of />-anisyl groups from peri-substituted naphthalenes...

The elimination of OH and H2 (20) from ortho and peri substituted alkoxy aldehydes, ketones or quinones is of diagnostic value for the location of functional groups113 114 The reaction sequence is restricted to systems containing such a substitution pattern. Investigations of 2H and lsO labelled model compounds establish the origin of neutral species (OH and H2) without clarifying the details of the complex skeletal reorganization. From the results it can only be concluded that the formation of stable oxonium ions, e. g., 105, is of importance. 

Sterical factors can be taken into account in analyzing the isomerizations of substituted aromatic compounds too this can be demonstrated, e.g., by considering methylated naphthalenes with peri-methyl groups. Isomerization of peri-substituted naphthalenes is characterized by two features by an anomalous facility of the reaction and by an apparent irreversibility of the process. These peculiarities are... 

The Japanese investigators who have studied the isomerization of peri-substituted polymethylnaphthalenes in CF3COOH have failed to explain many peculiar effects of the number and position of methyl groups on the kinetic parameters. 

The calculated values of R terms for the isomerization of peri-substituted polymethylnaphthalenes under complete protonation (8 = 1) are presented in Table 56 together with the experimental values of AG (at 5, = 1) for the conversions of 1,8-di-, 1,4,5-tri- and 1,2,3,4,5-pentamethylnaphthalenes. The differences in the relative ability to isomerize for various peri-substituted polymethylnaphthalenes... 

Table 56. Estimated and experimental values of free activation energy for isomeric transformations of peri-substituted polymethylnaphthalenes...

As the hydrogens of the peri positions in 1 are replaced by larger moieties, the repulsion energy increases and AG inv decreases relative to 1 (Table 1) [57, 62]. The order of barrier heights of some 2,3-disubstituted corannulenes determined experimentally follows oxygen (35, 9.9 kcal/mol) > phenyl (32, 9.4 kcal/mol) > bromomethyl (34, 9.1 kcal/mol), and aU these examples exhibit lower barriers than other non-peri disubstituted corannulene derivatives, such as 36 (9.9 kcal/mol) and 37 (10.4 kcal/mol). The lower barriers found for the peri-substituted compounds compared to that found for the same substituents in isolated positions shows the special contribution from peri X/X repulsion. Substitution at the peri positions as well as the 1,6-positions leads to a further reduction in the barrier, for example compound 38 (8.7 kcal/mol). From an assumption of additivity in steric bulk, one can assess the steric size of a peri substituent as being roughly OR < Ph=Cl < Me. 

Arnold et al. reported in 1988 [68] the synthesis of oligomeric or low molecular-weight polymeric metallocenes (M = Fe or Ru) in which the separate metallocene units are held proximate and face to face by the bridging peri-substituted naphthalene rings, 17. Cyclic voltammetry of the ferrocene oligomers shows... 

Ashbrook, S.E., Biihl, M., Slawin, A.M.Z. and Woollins, J.D., Noncovalent interactions in peri-substituted chalconium acenaphthene and naphthalene salts A combined experimental, crystallographic, computational, and solid-state NMR study, Inorg. Chem. 51 (20), 11087-11097 (2012). 

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