Alternant hydrocarbons substitution into

No defined complexes could be isolated from reactions of complex 1 with acetone Me2C=0. Complexes 2a and 2b react with acetone to give the zirconafuranone 2c, which is an interesting zirconocene precursor in view of its extremely good solubility in hydrocarbon solvents and because of its ability to dissociate into the alkyne complex [2f], It is also possible to cleanly substitute the bis(trimethylsilyl)acetylene unit so as to obtain the complex 47, or, alternatively, to substitute the acetone with formation of the zirconafuranone 95 (Fig. 10.14) [2f],... 

In substituted benzenes, the symmetry is lowered and the transitions into the states that correlate to the B2u and B u states of benzene become allowed by IPA, 2PA, or both. However, when the substituents induce only a weak perturbation on the benzene yr-electron system, the IPA or 2PA spectra of the substituted compounds often closely resemble the spectrum of the unsubstituted parent molecule. Various theoretical models have been developed in an attempt to predict the type of change in the band intensity and characteristics in the 2PA spectra of substituted benzenes and, more generally, of alternant hydrocarbons [34-36]. It was found that the effect of a perturbation is quite different for IP and 2P allowed transitions. In particular, 2P transitions to the state correlated to the benzene B2u state (Lb) are affected more by vibronic coupling than transitions to the state correlated to the benzene Biu state (La, in Platt notation [31,32]). In contrast, inductive perturbations enhance the La band more than the Lb band. The effects of vibronic coupling and inductive substituents are reversed for IP transitions into these states. Experimental... 

As a general treatment of the problem of substitution, Wheland s method has the disadvantage of not being very easy to apply. For one class of aromatic substances, namely the alternant hydrocarbons and heterocyclic compounds isoaromatic with them, a comprehensive and rapid treatment has been developed. Alternant hydrocarbons have no odd-numbered rings. They have the property that the constituent carbon atoms fall into two sets distinguished as starred and unstarred, such that no atom of one set is adjacent to another of the same set. Odd alternant hydrocarbons are radicals or ions. As an... 

An obvious extension of polyhedral silsesquioxane materials chemistry would be the incorporation of suitably functionalized POSS cages into important classes of thermoset resins, such as epoxy, phenolic, vinyl ester, styrene/divinylbenzene, acrylic resins and hydrocarbon networks. However, little has appeared in the literature, except for a few examples already discussed. This is an area in which our laboratory has become quite active. Two general types of substituted POSS monomers can be chemically incorporated into such resins. First, monofunctional monomers can be used. Alternatively, difunctional or polyfunctional POSS monomers can be used. Incorporating a monofunctional POSS monomer can actually lower flie resulting resin s crosslink density if the amoimt of the monofunctional POSS monomers in the commercial resin s monomer mixture is held constant. The POSS cages with organic functions attached to its comers have typical diameters of 1.2-1.5 run. Therefore, each POSS monomer occupies a substantial voliune. When that POSS... 

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