Cyclophanes strain energies

Cyclophane Strain Energy Cyclophane Strain Energy... 

The intra- and intermolecular interaction between cationic center and tt-electron system have attracted many chemists and much knowledge on the interaction has been accumulated (1). In 1975, we intended to apply such a kind of interaction to cyclopolymerization. Thus, it is expected that the transition state leading to a strained cyclic unit in the polymerization could be stabilized by the intramolecular attractive interaction between cationic growing-end and ir-system There had been few examples of cyclopolymerizations giving strained units. A paracyclophane unit was employed as a strained cyclic unit in the polymer main chain. In Table I are summarized some cyclophanes with their strain energies. 

Another example of thermodynamic product control is found in the cyclophane synthesis reported by Okada et al. [131]. They found that irradiation of 135 yielded exclusively 136 (Scheme 55), which had both cyclobutane rings in the exo orientation. Calculations revealed that the bis-exo cycloadduct 137 had 12 kcal moT less strain energy than the bis-endo adduct 139 and 6 kcal mol less strain energy than the exo-endo compound 138 (see Fig. 3). With energy differences of this magnitude, the selectivity exhibited by this... 

HEATS OF COMBUSTION AND STRAIN ENERGIES OF SOME CYCLOPHANES. 

We close is discussion by mentioning three more cyclophanes. The first is a triply layered species, all para in its benzene substitution, all with two methylene groups as linkages, l,4 2,5-[2.2.2.2]cyclophane (40). For the purpose of calculating strain energy, this... 

The substantial amount of strain in [6]paracyclophane (la) (Structures 1) and its lower homologues precluded ordinary synthetic methods for cyclophane synthesis. Viable alternative should therefore be based on transformation from high energy species such as strained molecules or reactive intermediates like... 

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