Cyclophanes spectroscopic properties

The cyclophane hexaene 29 has been synthesized via a sixfold Wittig reaction59. Spectroscopic properties and possible conformations of the hydrocarbon were discussed. Catalytic hydrogenation of 29 led to the polycycle 30. 

The chemistry of cyclophanes has been studied extensively by Cram and others (12), and their following spectroscopic properties are revealed Characteristic absorption around 11 y in IR spectroscopy (13), high field shift of aromatic protons in 1NMR spectroscopy due to the shielding effect of the opposite aromatic nucleus (14), abnormal absorption at ca. 240 nm and red-shifted, broad B-band in UV spectroscopy (15), red-shifted CT-band with TCNE in visible spectroscopy (VS) (14, 16), and characteristic properties in fluorescence spectroscopy (FS) (17, 18) and 13CNMR spectroscopy (19), which are discussed below. 

That in real life - in the laboratory of the synthetic chemist - the benzene rings do not have to be planar to display their aromaticity (as shown by their chemical and spectroscopic properties) became increasingly obvious when Cram s seminal studies on cyclophanes began to appear, hydrocarbons which are characterized by bent and battered rings (Cram). 

Larger cyclophanes have been used for metal coordination, too [92]. A recent example is the preparation of the disilver(I) complex of a conjugated polyene with [2.2.2]paracyclophane end groups (144) [93]. The NMR spectroscopic studies and X-ray structure analysis showed that the sites of complexation are exclusively the cyclophane groups and the olefinic spacers do not overly perturb the complexation properties of the cyclophanes. 

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