Molar ratio, donor/acceptor

Unless otherwise noted, the reaction was carried out using 1.0 mmol of Michael acceptors and donors (1 1) in 1.0 mL of solvent. The molar ratio of acceptor donor ruthenium is 50 50 1 (S/C = 50). Isolated yield after flash chromatography on the silica gel. Determined by HPLC analysis. dS/C = 100. eNot determined. -Determined by 13C NMR of the ketals derived from the products and (2R,3 )-butanediol. 

Bidentate ligand transfer also occurs between di- and mononuclear complexes via donor-acceptor intermediates. Reactions of the cationic complex [Au2(/i-dppm)2]2+ with [AuX2] (X = C1, Br) salts lead to tri- or dinuclear derivatives depending on the molar ratio (1 1 or 1 2) (Scheme 36).2645... 

Among the M(dmit)2-based superconductors, a-(EDT-TTF)[Ni(dmit)2] is also of donor-acceptor type and has two outstanding features it is the only one to contain a 1 1 molar ratio of donor and acceptor units and to exhibit superconductivity at ambient pressure [32]. It was found to be superconductive below 1.3 K under ambient pressure (Fig. 3). 

Figure 14 Fluorescence intensity ratio of acceptors at 417 nm and donors at 360 nm plotted against the molar fraction of MP-CUA in mixed LB films with (O) PA and ( ) AA The dotted line shows the calculated dependence by Forster energy transfer. 

For instance, Kochi and co-workers [89,90] reported the photochemical coupling of various stilbenes and chloranil by specific charge-transfer activation of the precursor donor-acceptor complex (EDA) to form rrans-oxetanes selectively. The primary reaction intermediate is the singlet radical ion pair as revealed by time-resolved spectroscopy and thus establishing the electron-transfer pathway for this typical Paterno-Biichi reaction. This radical ion pair either collapses to a 1,4-biradical species or yields the original EDA complex after back-electron transfer. Because the alternative cycloaddition via specific activation of the carbonyl compound yields the same oxetane regioisomers in identical molar ratios, it can be concluded that a common electron-transfer mechanism is applicable (Scheme 53) [89,90]. 

As shown in Box 2-3, the Henderson-Hasselbalch equation also allows us to (1) calculate pKa, given pH and the molar ratio of proton donor and acceptor (2) calculate pH, given pKa and the molar ratio of proton donor and acceptor and (3) calculate the molar ratio of proton donor and acceptor, given pH and pKa. 

In both cases the minimum donor - acceptor molar ratio demanded for the reduction of nitro- to amino group equals 3. 

The Henderson-Hasselbach equation is useful for calculating the molar ratio of base (proton acceptor) to acid (proton donor) for a given pH and pK or for calculating the pK, given the ratio of base (proton acceptor) to acid (proton donor). It can be seen that when the concentration of anion or base is equal to the concentration of undissociated acid (i.e., when the acid is half neutralized), the pH of the solu-tion is equal to the pK of the acid. 

The products (135) were obtained in excellent yields (<99%) with high enantiomeric excess (<96% de and <97% ee), even when only an equal molar ratio of the donor to acceptor was used.195... 

For the strong donor monomer VCZ, the photoreaction depends on the solvent basicity and the molar ratio of the donor and the acceptor. In strongly basic solvents such as dimethyl formamide (DMF), the radical homopolymerization of VCZ occurs in the presence of catalytic amounts of FN or diethyl fumarate (DEF), but it is replaced by radical copolymerization in an equimolar amount of the monomers. The cationic homopolymerization of VCZ, which proceeds in less basic solvents, e.g., benzene, and the cyclodimerization of VCZ, which proceeds in moderately basic solvents, e.g., acetone, is accompanied by the radical copolymerization of VCZ with FN or DEF [6],... 

The diradical nature of the intermediate in the copolymerization of monomers through a charge transfer intermediate has been suggested by Zutty et al. (88) as a result of studies on the copolymerization and terpolymerization of monomer systems containing bicycloheptene and sulfur dioxide. The third monomer apparently enters the copolymer chain as a block segment, while the donor-acceptor monomer pair enter the chain in a 1 1 molar ratio, irrespective of the ratio present in the monomer mixture. 

The reactions were carried out in benzene or aqueous methanol at 353 K. Mostly a high amount of catalyst was used (molar ratio ketone Fe(II)ion = 1 to 14). The activity of the FePc derivative is higher than that of low molecular unsubstituted FePc or other MPc. The activity of the Fe containing catalysts may be due to redox reactions abstracting halogen atoms. Therefore the FePc s support the electron transfer from the donor to the acceptor (Eq. 51). 

In comparing the thiourea-nitrate inclusion compounds with the thiourea-bicarbonate inclusion compounds, it is noted that the oxygen atoms of the NOJ ion, unlike the HCOJ ion, can only form acceptor hydrogen bonds with other potential donors. Therefore, the construction of a two- or three-dimensional host framework requires a higher thiourea/nitrate molar ratio, with or without cocrystallized water molecules, as is the case in complexes 2.5 and 2.6. In the 1 1 complexes 2.7,2.8, and 2.9 only a parallel arrangement of separate ribbons can be constructed from the thiourea and nitrate building blocks. 

Bi-directional flux of free cholesterol between cells and lipoproteins occurs, and rate constants characteristic of influx and efflux can be measured [17]. The direction of any net transfer of free cholesterol is determined by the relative free cholesterol/phospholipid molar ratios of the donor and acceptor particles. Cholesterol diffuses down its gradient of chemical potential generally partitioning to the phospholipid-rich particle. Such a surface transfer process can lead to delivery of cholesterol to cells. This mechanism operates independently of any lipoprotein internalization by the receptor-mediated endocytosis. The influence of enzymes such as lecithin-cholesterol acyltransferase and hepatic lipase on the direction of net transfer of free cholesterol between lipoproteins and cells can be understood in terms of their effects of the pool sizes and the rate constants for influx and efflux. 

Fig. 1.15 Fluorescence spectra of nanospheres dispersed in water with different molar ratios between donor (D) and acceptor (A). [D] = 49.7 mM. [D] to [A] molar ratio is 352 1, 176 1, 88 1, 58 1, 44 1 from bottom to top. = 375 nm. Adapted from Ref. [113]...

With different molar ratios between the donor and acceptor, the acceptor emission amplified significantly as the ratio of the donor increased. Eventually, the energy transfer was saturated at the 1 352 ratio of acceptor and donor, when the maximum acceptor emission amplification reached a factor of 35, which is much higher than that of other artificial light-harvesting systems. 

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