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

Abstract

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. The &value is -0.96. In both reactions the [I 4lannulene is more reactive than 1,6-methano[I Olannulene at the corresponding 2position, for which the partial rate factors are 1.03 x 1 O7 and 9.27 x 1 03, respectively, with G + -0.80.The reactivity difference towards exchange is 4.4-fold greater than that which exists between the corresponding 1 -positions of anthracene and naphthalene, as predicted by topological resonance energy calculations. These calculations also predict the observed greater reactivity of the annulenes compared with the corresponding polyacenes. The detritiation and desilylation data predict a 0value for the [14]annulene of -0.65, cf. -0.435 for the [lO]annulene. The difference 0 ' -0 is therefore 0.31 for the [I 4]annulene, compared with 0.32 for the [I Olannulenes, indicating that the [I 4lannulene is marginally less polarisable. Lithiation of the [I 4lannulene occurs preferentially at the 2 -position.

Annulenes, 1980–2000

“…110 Partial rate factors for protodetritiation and protodesilylation of 2-substituted derivatives of 68 have been measured. 111 Reduction of bridged [14]annulenes with lithium provides strongly coloured dianions. 78 The dianions are paratropic; their relative paratropicities reflect the conformational changes in a much more sensitive way than the diatropicities of the neutral annulenes, and further reveal the interdependence of steric and conjugative effects in the molecules.…”

The Low‐Temperature UV/VIS Absorption Spectrum of [14]Annulene

“…The quantitative electrophilic reactivity of the [14]annulenes was studied by Laws and Taylor [47]. Quantum-chemical computations were done by Destro et al [48] comparing the X-ray structures of syn-1,6:8,13-diimino[141annulenes with connected bridges to their MIND0/3 computed geometries, by Vogler and Mitchell computing by the n-SCF force-field method 'H-NMR chemical shifts and geometries of [14]annulenes and their dianion salts [49], as well as of dihydropyrene and several of its benzo-annelated derivatives [SO], and by Cremer et al [51] investigating the configurational stability of oxido-bridged [14]annulenes by HF/STO-3G, HF/4-3 IG, MP2/STO-3G, MNDO and correlation-corrected MNDO calculations.…”