Donor solvent effects, rules

In summary, if the different contributions are considered as additive, one can see that the solvent strongly rules the capacity of CoPc to accept electrons from a generic donor, since m values almost double in going from gas phase to solution, while the surface plays a minor role. On the other hand, both solvent and surface effects increase the reactivity of the adsorbed species, the total intermolecular hardness being less than one-half of the gas-phase values (3.0 vs. 1.3 eV, respectively). 

Rate measurements are straightforward if the carbenes can be monitored directly. As a rule, the decay of carbene absorption is (pseudo) first-order, due to rearrangement and/or reaction with the solvent. In the presence of a quencher, the decay is accelerated (Eq. 1), and the rate constant kq is obtained from a plot of k0bs versus [Q], Curved plots were often observed with proton donors (HX) as quenchers, particularly for high concentrations of weakly acidic alcohols. Although these effects have been attributed to oligomerization of the alcohols,91 the interpretation of curved plots remains a matter of dispute.76 Therefore, the rate constants reported in Tables 2-4 are taken from linear (regions of) obs-HX plots, or refer to a specified concentration of HX. 

The media represented in Table 10 contain, as a rule, a protic component but in small amounts. However, the content of proton donors can be increased appreciably hydrogenation of benzene can be effected in mixtures of water and aptotic solvents (such as diglyme, ethylenediamine, sulfolan. Table 11). Furthermore, benzene can be reduced not only in a mixture of aptotic and protic solvents but often in protic media as well. Mono- and dibasic alcohols and also water (Table 11) proved to be suitable for the purpose. Although the presence of tetrabutylammonium cations enhances to some extent the dissolution of benzene in an aqueous phase. 

An important achievement of the early theories was the derivation of the exact quantum mechanical expression for the ET rate in the Fermi Golden Rule limit in the linear response regime by Kubo and Toyozawa [4b], Levich and co-workers [20a] and by Ovchinnikov and Ovchinnikova [21], in terms of the dielectric spectral density of the solvent and intramolecular vibrational modes of donor and acceptor complexes. The solvent model was improved to take into account time and space correlation of the polarization fluctuations [20,21]. The importance of high-frequency intramolecular vibrations was fully recognized by Dogonadze and Kuznetsov [22], Efrima and Bixon [23], and by Jortner and co-workers [24,25] and Ulstrup [26]. It was shown that the main role of quantum modes is to effectively reduce the activation energy and thus to increase the reaction rate in the inverted... 

Cqpolymerization of MCM with traditional monomers is the main technique of metal insertion into a polymer chain, and it is more widely used than their homopolymerization. However, ocpolymerization laws in such systems are difficult to analyze because of their raultiparameter dependence of the kinetics and copolymerization characteristics on the process, parameters such as pH, solvent nature and even concentration ratio (30). The metal-containing giroup in MCM is, as a rule, an electron-donor substituent (scheme Q-e). The copolymerization yields complexes of different comonomers, effecting the polymer composition and structure. In our view, the most remarkable one is cqpolymerization of transition metal diacrylates with MMA, styrene, etc. (37), as well as vinylpyridine and vinylimidazole MX complexes and formation of ternary copolymers of the following composition (38) ... 

In an interesting paper it is revealed that di-t-butylnitroxide (DTBN) radical induces upheld contact shifts for the X-H proton donor molecules and conforma-tionally dependent downfield shifts for C—H protons in accordance with the W-rule. Methyl protons in close spatial contact with the N-H or O-H proton donor groups exhibit marked DTBN-induced downfield pseudo-contact shifts. The origin of these effects and their potential uses are discussed. Proton shifts for various monoterpenes e.g. camphor, camphor quinone, and pinocarvone) in hexafiuorobenzene are compared with the shifts obtained in other, more conventional, solvents. Unusually large couplings between the OH and adjacent CH protons have been observed for extremely pure samples of syn- and anrt-7-hydroxynorbomene in particular solvents. " The simplification in the spectra of these compounds, of 7-hydroxynor-bornadiene, and of the catalytically deuteriated (exo-addition) derivatives, with the aid of Eu(dpm)3 and Eu(fod)3 is reported in a companion communication. ... 

---