Strain influence, cyclophanes

Coordinated and uncoordinated cyclophanes receive considerable interest due to the influence of strain on aromaticity [69]. Benzannulation adds a mild synthetic strategy to the known synthetic methods for their production, especially for coordinated cyclophanes, which have been mostly synthesized by the harsher direct coordination of pre-assembled cyclophanes. 

However, on top of the inclusion phenomena, cyclophanes have more interesting properties to offer. In his first publication on cyclophanes, Cram [13] had already expressed his opinion about some peculiarities to be expected in cyclophanes, which he outlined as follows a) electronic interaction between aromatic rings placed face to face , b) the resulting influence on substitution reactions in the aromatic rings by transannular electronic effects, c) intramolecular charge transfer complexes and d) ring strain, steric strain and transannular strain. These effects have been studied on the parent compounds in detail [3]. 

Dodziuk et al studied the chemieal shifts and SSCCs in the NMR spectra of strained [2.2.2]cyclophanes using experimental measurements and DFT calculations. The results demonstrated the influence of strain on the NMR parameters studied. In spite of the strain, the calculations reproduced the... 

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