Conjugated n-systems

The dimension of the matrix is the number of atoms in the n conjugated system. Let us take the three-carbon system allyl as our next step. Concentrate on the end... 

Table 5 Structures and properties of silole-acetylene n-conjugated systems ...

Silyl cations like 3 and 7 in which the positively charged silicon is part of a n-conjugated system attracted particular interest. The marginally stable silatropylium ion 7, is characterized by a Si NMR resonance at 8 Si = 149 in CD2CI2 at —50 °C, downfield-shifted by 192 ppm compared to the precursor silane.This experimental value is in fair agreement with the calculated silicon NMR chemical shift for the optimized gas phase structure of 7 (8 Si = 159.9, at GIAO/HF/6-311 + G(2df,p)(Si), 6-31G(d) (C,H)). This indicates only small interactions between the cation and dichloromethane, the solvent used for the NMR investigations. 

The presence of ji-ji or n-n conjugated systems does not assure absorption of visible light or generation of color. However, all colored organic compounds, including pigments, possess extended conjugated resonance systems. Thus, whereas 1,4-diphenylbutadiene is colorless. 1,6-diphenylhexatriene is colored. 

Many of the above deficiencies were removed in further refinements of the Hiickel method, which was anyway made obsolete by the development of ab initio and DFT techniques. Still, organic chemists adhere to the original Hiickel description, which is often sufficient to make qualitative predictions about the nature of n-conjugated systems. In particular, the Hiickel model finds widespread use in porphyrinoid chemistry. The so-called annulene model, which will be used throughout this review, is outlined below for the parent porphyrin macrocycle. 

Synthesis of [1 OjCyclophenacene n-Conjugated Systems from [60jFullerene I 67... 

Design of n-Conjugated Systems Using Organophosphorus Building Blocks... 

Synthetic Approaches to Highly Annelated Chiral n-Conjugated Systems... 

Structures, Reactions and Functions of d-d and d-n Conjugated Systems Editors A. Nakamura, N. Ueyama, K. Yamaguchi... 

Detailed calculations on reactants visualized as oblate spheres have shown that Hel also depends on the shape and nodal character of overlapping orbitals [56]. Thus, Hel for planar n-conjugated systems is predicted to vary depending on the relative orientation of the molecules (Fig. 15 and 16). Orbital character has special importance in PET where overlap between orbitals of the quencher and the rapidly oscillating wavefunctions of the excited reactant determines the extent of electron coupling. 

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