S-acceptor

Use HYBOT s acceptor and donor enthalpy factors to estimate the optimum H-bonding energy via Eq. (3), 

Table 2.S Acceptor level of strained GaAs after lattice relaxation

Gutmann s acceptor number Linear Solvation Energy Relationships (0 hydrogen-bond parameters) 

The Gutmaim s Acceptor Number (AN) was proposed [Gutmann, 1978] as a quantitative empirical parameter of solvent hydrogen bond acidity based on P-nmr shifts of thiethylphosphine oxide at infinite dilution, calculated as AN = -6 " 2.349. 

Schematic reaction Reaction type Donor(s) Acceptor(s)

Fig. 4.3. The spherical polar angles 6, 0 used to define the direction of approach of an N - H donor to the lone pairs on an (AA)2-C=S acceptor group

Fig. 5.20 Plot of AV2 for CH3CN (o) and CD3CN (o) in more acidic solvents against the solvent s acceptor number AN. The best straight lines were estimated without the data for F and NMF. The data for CD3CN have been shifted vertically by 20 cm for clarity. (From reference 33, with permission.)

Fig. 7.7 Plot of the logarithm of the rate constant for reaction (7.3.23) in various solvents against the solvent s acceptor number AN (table 4.10).

A model has been proposed which allows an empirical prediction of reactivity for this class of compound. Accordingly, if R or are donor-type substituents or R or R acceptors, the substrates (20) are ODPM reactive. The complementary pattern of substituents (R or R s acceptors or R or R = dtxiors) is characteristic of the unreactive enones. Bicyclo[3.2.2]n(Mienones (64c,d no reaction. Scheme 12, Section 2.6.3.4.1) and mixed bicyclo[2.2.2]octenones (20e 21e Scheme 11, Section 2.6.3.4.1) need not 

Figure 3. (a) Stereoview of the crystal structure of thiourea. Note that the hydrogen-bonded shoulder-to-shoulder ribbons run parallel to the caxis and each S atom forms four N-H - S acceptor hydrogen bonds, (b) The hydrogen-bond framework in crystalline thiourea viewed along the caxis. (Data from ref. 48). 

Solvent-induced frequency shifts have also been studied for dimethylsulfoxide (DMSO), which is a strong Lewis base. Most solvents behave as Lewis acids and interact with DMSO via the electron density on the — S=0 group. This interaction leads to a red shift for this band which is as large as 56 cm in the presence of acetic acid [34]. The magnitude of the shift correlates well with the solvent s acceptor number giving the relationship 

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