Computation of the ESR. Coupling Constants of the [16]Annulene Radical Anion; Theoretical and Experimental Reinvestigation of the Excited States of [16]Annulene and its Mono‐ and Dinegative Ions

Abstract

SummaryThe problem of assigning the two small ESR. coupling constants of the [lblannulene radical anion to the two sets of four equivalent outer and inner ring protons is treated by three different semiempirical MO methods. All three methods indicate that the smaller coupling constant (0.743 Gauss) should be assigned to the inner protons, and the larger one (0.963 Gauss) to the outer ones. The electronic spectra of [ 16]annulene, its radical anion, and its dianion have been remeasured. Especially interesting was the detection of a symmetry-forbidden band of the radical anion at 1473 nm (6789 cm-', logc 2.57). The spectra are discussed in terms of different MO models.

Magnetic Circular Dichroism of Nonaromatic Cyclic π-Electron Systems. 5. Biphenylene and Its Aza Analogues

“…Two modifications of the original complete neglect of differential overlap/spectroscopic (CNDO/S) method were used, one due to Baumann and Oth and the other to Dick and Hohlneicher . Both of these calculations and also the LCOAO calculation 15 used the experimental geometry of 1 , and this was used for the LCOAO calculations on aza derivatives of 1 as well.…”

One-Pot Synthesis ofN-Substituted Diaza[12]annulenes

“…Annulenes have attracted much attention since the first report on [8]annulene in 1911 . Many efforts have been devoted to probing the (anti)aromaticity of [4 n ]annulenes by using NMR spectroscopy and computational methods. − The addition of π-electrons to the [4 n ]annulenes that are antiaromatic in the Hückel sense has been carried out to alter their aromaticity and magnetic properties. − Among the [4 n ]annulenes, studies on [12]annulenes and hetero[12]annulenes are very limited due to their decreased thermal stability. ,− Stevenson reported that [12]annulenes show diamagnetic properties 10a…”