Electrophilic aromatic substitution. Part 18. Protiodetritiation of anthracene, coronene (dibenzo[ghi,pqr]perylene), and triphenylene in anhydrous trifluoroacetic acid

Application of Electron Delocalization Indicators in the Study of Electrophilic Aromatic Substitution Reactions

“…The MESP topography in several of these molecules is shown in Figure 20. The central rings of triphenylene, perylene and coronene have no MESP minima, in agreement with the consideration that these rings are empty [2,114]. A Clar's aromatic sextet [115] in the central ring of triphenylene and coronene prevents the existence of another sextet in these molecules (see for example Figure 21(a)), while it is not possible to draw a sextet in the central ring of perylene.…”

The quantitative electrophilic reactivity of annulenes. Part 3. Partial rate factors for protiodetritiation and protiodesilylation of 1,6 : 8,13-propane-1,3-diyldene[14]annulene

“…It was assumed that tritium would preferentially enter the 2-position in view of the qualitative results for electrophilic substitution of (4), ' and this was confirmed by the results for desilylation, below. The [ 14)annulene is like the [ 10]annulene, unstable under the standard conditions for acid-catalysed hydrogen exchange uiz. anhydrous trifluoroacetic acid at 70 "C. Runs were therefore carried out with 50:50 v/v Aristar acetic acid in pure trifluoroacetic acid, using 9 vols of this mixture to 1 vol of chloroform (to aid solubility) at 25 "C. The compound gave excellent first-order kinetics, indicating that the next most reactive site in the molecule must be at least lo2 less reactive.…”

“…9 1 ~ acids,I2 in excellent agreement with the value obtained with the [ 14lannulene. The 9.0-fold rate difference between the [14]-and [lO]-annulenes may therefore be used with confidence.…”

“…

We have prepared 1,6: 8,13-propane-I ,3-diylidene [14]annulene with tritium and trimethylsilyl su bstituents at the 2-position. Rates of protiodetritiation and protiodesilylation have been measured, leading t o partial rate factors, under standard conditions, of 2.0 x 1 O8 (trifluoroacetic acid at 70 "C) and 8.34 x l o 4 ( 2 : 5 v/v perchloric acid-methanol at 5 0 "C), respectively.

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“…spectrum of its dication.6 Similar interactions have been identified in the electronic spectrum of 1,6: 8,13-propane-1,3-diylidene[ 14lannulene (4),' confirmed [and also for (l)] by their photoelectron spectra.' No reactivity data are yet available for (4), or indeed for any [14]annulene, and in order to provide information on the reactivity of (4) compared with (l), we have undertaken a quantitative kinetic study of electrophilic substitution of the former.…”