Linear polyenyl cations

Table IV. STO-3G Calculated Bond Lengths for Linear Polyenyl Cations...

Figure 3. Idealization of resonance forms found for linear polyenyl cations...

Figure 4. Energy of conjugation for linear polyenyl cations (Ln+ = CnHn+2+)...

There are a variety of methods for the computation of the MOs that interact in the transition states of [4+2]-cycloadditions. The LCAO method (linear combination of atomic orbitals) is often employed, and the basic idea is as follows. The MOs of the -systems of alkenes, conjugated polyenes, or conjugated polyenyl cations, radicals, or anions all are built by so-called linear combinations of 2p AOs. In a somewhat casual formulation, one might say that the MOs of these -systems are constructed with the help of the 2pz AOs. These AOs are centered at the positions of the n C atoms that are part of the -system. LCAO computations describe a conjugated -electron system that extends over n s/ 2-hybridized C atoms by way of n Ji-type MOs. 

Table VIII. Conjugation Energies for Linear a,a>-Dimethyl Polyenyl Cations (kcal/mol)...

Figure 6 Dependence of non-bonded resonance stabilization energies, Fnobo, of linear a.ll-trans polyenyl cations CH2-(CH=CH) -H on the chain length n...

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