Two molecules areisoconjugateor, more strictly,isohyphen;pgr;hyphen;electronicif they have the same number and geometrical arrangement of pgr;hyphen;electrons bound about equally tightly in a planar conjugated system. Their pgr;hyphen;electron spectra then show close resemblances. Example: anilinehyphen;styrene.Avariconjugate sequenceis a series of such molecules in which the binding of some of the pgr;hyphen;electrons and the appearance of the spectra slowly changes. Example: fluorobenzene (isohyphen;pgr;hyphen;electronic with benzene), phenol, aniline (isohyphen;pgr;hyphen;electronic with styrene). Here the heteroatoms are formally saturated and no transitions of nonbonding electrons (nhyphen;bands) are observed. Second example: phenyl cyanide (almost isohyphen;pgr;hyphen;electronic with benzene), benzaldehyde, phenyl azomethane (isohyphen;pgr;hyphen;electronic with styrene). Here the heteroatoms are formally conjugated andnhyphen;bands appear at long wavelengths in addition to the pgr;hyphen;spectra. The location of the pgr;hyphen;bands partly determines that of thenhyphen;bands.The pgr;hyphen;spectrum of every organic molecule with a closedhyphen;shell ground state lies on a variconjugate sequence between the pgr;hyphen;spectra of two conjugated hydrocarbons.Several such sequences involving 90hyphen;odd compounds are displayed, showing the different binding of pgr;hyphen; andnhyphen;electrons by different heteroatoms, and the interaction ofnhyphen;bands of neighboring heteroatoms.An examination is made of the general problem of assigning observed electronic transitions in organichyphen;molecule spectra to particular theoretically predicted transitions. It is shown how variconjugate sequences could be useful in making such assignments.
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