Interactions cyclophanes

Reddington, M.V. (1989) Non-covalent bonding interactions cyclophanes, catenanes, and rotaxanes, PhD. Thesis, University of Sheffield. 

Cyclophanes or 7r-spherands have played a central role in the development of supramolecular chemistry forming an important class of organic host molecules for the inclusion of metal ions or organic molecules via n-n interactions. Particular examples are provided by their applications in synthesis [80], in the development of molecular sensors [81], and the development of cavities adequate for molecular reactions with possible applications in catalysis [82]. The classical organic synthesis of cyclophanes can be quite complex [83], so that the preparation of structurally related molecules via coordination or organometallic chemistry might be an interesting alternative. 

These structural data demonstrate that 12 is a rather less distorted molecule than [2.2]paracyclophane. However, a dramatic effect of the strong cr(Si—Si)—w interaction was observed in UV spectra as shown in Fig. 5. In the UV spectrum of phenylpentamethyldisilane, an intramolecular crfSi—Si)—7T charge-transfer band appears around 231 nm (11a, 12). Octamethyltetrasila[2.2]ortho- (15) and metacyclophane (16) show similar absorptions, but the band splits into two bands at 223 nm (e = 19,100) and 263 nm (e = 22,500) in 12. This type of red shift in the UV spectra occurs only in 12 among other polysilapara-cyclophanes such as 13 and 14. 

To date the structure and reactivity of numerous complexes derived from aromatic compounds and nitrosonium cation have been studied (5, 56-63). However, relatively few studies are available on the nitrosonium complexes of cyclophanes (5, 57, 59, 61, 62), cf ref. (63). The interaction of [2.2]paracyclophane with nitrosonium tetrachloroaluminate was studied by H and 13C NMR spectroscopy using deuterium isotope perturbation technique (64). It was found that the resulting nitrosonium complexes containing one (25) or two NO groups (26) are involved in fast interconversion (on the NMR time scale) (Scheme 17). 

A) almost equals the van der Waals distance. As in [2.2]para-cyclophane, the hydrogen atoms of the aromatic moieties are directed towards the interior of the molecule because of the increased -electron density on the outside of the molecule caused by the intraannular interaction of the 7r-electron clouds. 

The IR spectrum of the pseudo-geminal 46) 4-acetyl-13-bromo[2.2]para-cyclophane (18) shows a band for the carbonyl stretching vibration at 1663 cm-1. This frequency lies outside the range of frequencies (1666—1668 cm-1) found for the absorption of other isomers and has been attributed by Reich and Cram to transannular Br...C=0 interactions. 

There are several types of natural and synthetic molecular hosts, such as cyclodextrin and cyclophane, that are shaped to accommodate neutral and charged organic molecules in the three-dimensional cavity. The inclusion complexation by molecular hosts is driven by various weak forces like van der Waals, hydrophobic, hydrogen bonding, ion-dipole, and dipole-dipole interactions, and therefore the molecular recognition process seems much more complicated. In expanding the scope of the present theory, it is intriguing and inevitable to perform the extrather-... 

Photoelectron spectra (PES) of helicenes have been measured to trace whether interactions between the orbitals of overlapping benzene rings occur. Evidence for such interactions has been found for cyclophanes 118, ll9) bands from symmetry-equivalent n-orbitals of the benzene rings in these compounds were split due to transannular jt-Jt-overlap. 

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