Spectrum delocalised system

In this form it has the structure of a bridged delocalised 10 TT-electron system, which is presumably energetically preferred to a peripheral delocalised system involving 16 tr-electrons, since the former involves a (4m + 2) ir-electron system and the latter a (4m) system. The chemical shifts in the H-n.m.r. spectrum of the dianion agree with this interpretation in that any charge-induced upfield shift appears to be neutralised by the effect of a diamagnetic ring current. 

The formation of anion radicals by chemical or electrochemical reduction may provide information about electron delocalisation in an inorganic ring system through the determination of the EPR spectrum in conjunction with molecular orbital calculations. In practice, however, the LUMO of the homo- or heterocycle is often an antibonding orbital. Consequently, occupation of the LUMO... 

A tropylium ion reacts at the 8-position to give a product which, on treatment with triphenylmethyl tetrafluoroborate, gives the interesting salt (XLIV), which forms dark blue crystals and whose n.m.r. spectrum indicates that the positive charge is delocalised over the whole ditropylmethyl system [367]... 

It is worth noting that fine features in the valence spectrum of ternary alloys are mainly due to rearrangements of delocalised states near the Fermi energy, and, consequently, they cannot be reproduced correctly with cluster models which use very small clusters. For this reason, it is better to use band structure methods for the systems under consideration. 

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