Monomer fragmentation

The oxidation of PH ([PH] is the concentration of the monomer fragments (in mol kg-1)) proceeds by the chain mechanism when the initiation rate is not very high, i.e., when 2ktVi < /cp2[PH]2 (see Chapter 2). The oxidation rate for very long chains is the following ... 

The reaction of diethylzinc with acetylacetone (acacH) in toluene resulted in the dimeric compound [EtZn(acac)]2 (39), which consists of a four-membered Zn202 ring . The El mass spectrum of 39 displayed three groups of peaks, attributed to the [Zn(acac)2] (miz 262), [EtZn(acac)] (m/z 192) and [Zn(acac)]+ (m/z 163) ions. The ion with m/z 192 simply represents a monomer fragment, whereas the ion with m/z 262 can be written as [M- EtiZn]. ... 

Spectroscopic analysis revealed that the thermally initiated [3 + 2] polycycloaddition produced 1,4- and 1,5-substituted triazole isomers in an approximately 1 1 ratio. This ratio appears to be statistic and dependant on the bulkiness of the organic moieties. For example, hfr-r-P[30(4)-20] with butyl spacers contained slightly more 1,4-triazole isomers than did hb-r-P[30(6)-20] with hexyl spacers. This becomes clearer if we look at the proposed transition states a and b of the [3 + 2]-dipolar cycloaddition (Scheme 16). Because of their molecular orbital symmetry, the acetylene and azide functional groups arrange in two parallel planes, a so-called two-plane orientation complex [48], which facilitates a concerted ring formation. If the monomer fragment or the polymer branch ( ) attached to the functional groups are bulky, steric repulsion will come into play and transition state a will be... 

The intermediate involved in the first process is indicated to be the monomer fragment, CpMoCCO), by the following (i)... 

We expect that the judicious selection of a core unit, internal monomer subunits, and terminal monomer fragments will allow the design of dendrimers to complex with specific guest molecules and to deliver them to specific sites. It will, of course, be essential to develop synthetic schemes that allow for chemical control and fidelity. 

In the vacuum pyrolysis of PTFE, the mass spectrum (Fig. 37, bottom trace) appears nearly identical to that of the monomer (Fig. 36, bottom trace) but different from that of the perfluoro-n-alkanes (Fig. 36, top and middle traces). This agrees with the known fact that pyrolysis generates almost the monomer fragments [36]. 

Mass spectrometric analysis of monomer fragments before and after ignition of the plasma ... 

The consequences of these alternatives are different each of the first two products contains three monomer units, but in the third alternative, we go directly from two-monomer fragments to a product with four monomer units. Since the reactivity of the —OH group or of the —CO2H group in all these reactants is quite similar, there is no particular preference among them, and the rates of the various reactions will depend mainly on the concentrations of the particular reactants. 

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