Parameters resonance

It is observed that solvolyses of the tertiary benzylic / nitrobenzoates A, B and C are correlated by Yukawa-Tsuno equation with reduced resonance components as indicated by a lower coefficient of the resonance parameter r. Offer an explanation. 

Table 17.6 Nuclear magnetic resonance parameters for the halogen isotopes...

The two-center one-electron integrals given by the second equation in (3.74) are written as a product of the corresponding overlap integral times the average of two atomic resonance parameters, (3. 

Here we will not discuss these problems and the intriguing observation that am and strong correlation which is, however, difficult to explain (reviews Charton, 1981 Cook et al., 1989 Hansch et al., 1991). These questions were intensively studied in the 1970s and 1980s, leading gradually to the development of field and resonance parameters denoted by F and R respectively (after an original proposal of Swain and Lupton, 1968), which can be considered as independent of each other. The secondary parameters R + and R reflect the potential for an additional mesomeric donor-acceptor interaction (as in 7.7, and the opposite type with a donor instead of NQ2 and the reaction site as acceptor). 

Examples of the successful application of such dual substituent parameter (DSP) treatments with field and resonance parameters will be discussed in Sections 8.3 (hydroxy-de-diazoniation) and 10.5 (Sandmeyer reaction). 

In the form of treatment developed by Taft and his colleagues since 195660-62, the Hammett constants are analyzed into inductive and resonance parameters, and the sliding scale is then provided by multiple regression on these. Equations 5 and 6 show the basic relationships. 

In the area of spectroscopy, the application, with computer assistance, of the theory to observed spectra should provide much readier access to magnetic resonance parameters (e.g., radical jr-factors, absolute signs of a- and J-values) than has been available hitherto. Moreover, for rtidical parameters, CIDNP is much more versatile than e.s.r. spectroscopy, since it can readily handle even very reactive radicals. 

Inductive and resonance parameters, (Tr°, ct, were evaluated for the isocyanide ligand from F chemical shifts they suggest that the isocyanide is a good cr-donor and a weak ir-acceptor. 

Vaara, J. (2007) Theory and computation of nuclear magnetic resonance parameters. Physical Chemistry Chemical Physics, 9, 5399-5418. 

Once the equation was well founded it became a tool for establishing a scale of resonance parameters based uniformly on infrared intensities, and particularly for measuring values of substituents which had not been obtained in other ways. It should, of course, be noted that the above equation could not give the sign of for any given substituent, since... 

Marriott and Topsom have recently developed theoretical scales of substituent field and resonance parameters. The former correspond to the traditional inductive parameters but these authors are firm believers in the field model of the so-called inductive effect and use the symbol The theoretical substituent field effect scale is based on ab initio molecular orbital calculations of energies or electron populations of simple molecular systems. The results of the calculations are well correlated with Op values for a small number of substituents whose Op values on the various experimental scales (gas-phase, non-polar solvents, polar solvents) are concordant, and the regression equations are the basis for theoretical Op values of about 50 substituents. These include SOMe and S02Me at 0.37 and 0.60 respectively, which agree well with inherent best values in the literature of 0.36 and 0.58. However, it should be noted that a, for SOMe is given as 0.50 by Ehrenson and coworkers . 

A table of correlations between seven physicochemical substituent parameters for 90 chemical substituent groups has been reported by Hansch et al. [39]. The parameters include lipophilicity (log P), molar refractivity MR), molecular weight MW), Hammett s electronic parameters (a and o ), and the field and resonance parameters of Swain and Lupton F and R). 

S. Sinnecker, E. Reijerse, F. Neese and W. Lubitz, Hydrogen bond geometries from paramagnetic resonance and electron-nuclear double resonance parameters Density functional study of quinone radical anion-solvent interactions, J. Am. Chem. Soc., 2004, 126, 3280. 

The F and R parameters are qualitatively analogous to the field and resonance parameters, 5 and SR, of Swain and Lupton19 that is, they measure the a and 7r-electronegativities, respectively, of substituents. However, the F and R values are more appropriate for correlating processes in which a localized positive charge develops than are the S and 91 values. Hence the F and R values correlate lone pair ionization potentials and proton affinities better than the corresponding and 91 values do. 

Taft and Topsom151 have fairly recently written an extensive review of the electronic effects of substituents in the gas phase. This article includes a tabulation of substituent inductive and resonance parameters. The inductive parameters (designated Op) are based on measured spectroscopic properties in either the gas phase or in hydrocarbon or similar solvents. The resonance parameters were arrived at through the treatment of 38 gas-phase reactivity series by iterative multiple regression, using the cr values of Bromilow and coworkers155 as the starting point. The of value for NO2 was found to be 0.65 (quoted... 

There is a further problem regarding a value for the resonance parameter of NO. The infrared method (Section V.A) yields a rri]K value of 0.07154, cf 0.31 or 0.25 above. 

The resonance effects of these groups are greatly enhanced when they are exerting an influence on highly electron-demanding processes. This topic will be discussed later. Here we shall be concerned with the resonance effects as shown under milder conditions and measured either by o()R or by a (BA) (Section II.B). For brevity we shall refer to the latter simply as or. The distinction between the two types of resonance parameter is important with —I groups, cf the nitro group (Sections in.C and V.D). 

The revised version246 developed new scales of field and resonance parameters, the awkward symbols, T and 3i being replaced by the more straightforward F and R. Some of the criticism made of the earlier form of the treatment had been met by the modifications, but the critics were still not satisfied247-249. 

Fields, R., Green, M., Jones, A. Bis(trifluoromethyl)phosphine Solvent Effects on Nuclear Magnetic Resonance Parameters. J. Chem. Soc. A, 1969, 2740. 

Schmidt, R. L., Butler, R. S., Goldstein, J. H. The Role of Polar Factors in Collision Complex Models for the Solvent and Concentration Dependence of Nuclear Magnetic Resonance Parameters. J. Phys. Chem. 73, 1117 (1969). 

Points 2 and 3 are characterized by the same value for the (homo-lytic) bond dissociation energy. However, resonance stabilization of charges can occur only for the heterolysis represented by point 3, Therefore in this case, the resonance parameter R has a high value, whereas it is zero for the heterolysis represented by point 2. 

Positive slopes in partial correlations of small series for which the Taft equation is suitable. For a resonance parameter r = 0.8. 

The frequency of a single-mode laser inside the spectral gain profile of its active medium is mainly determined by the eigenfrequency of the active laser cavity mode. Therefore any instability of resonator parameters, such as variation of cavity length, mirror vibrations or thermal drifts of the refractive index will show up as frequency fluctuations and drifts of the laser line. 

Memory, J. D. (1968). Quantum Theory of Magnetic Resonance Parameters. McGraw-Hill, New York. 

The partially occupied 17eag orbital is of greatest interest in the interpretation of magnetic resonance parameters. As Table I shows, this orbital is split off from the other copper 3d levels, and is almost pure a spin, with only 0.14% population in the spin-down atomic orbital. As written, the orbital is nearly pure imaginary for example, the coefficients of Y22 and Y2-2 are nearly... 

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