McConnell relationship

First, the hyperfine splitting conferred on the ESR spectrum of a 7t-radical by interaction of the electron spin with a proton is proportional to the 7t-spin population p, at the atom bearing the proton (the McConnell relationship).17 Thus, for a proton attached to carbon atom i the hyperfine splitting a(H),-is given by Eq. (1), where QCH is the spin polarization parameter for the C—H bond. 

When methyl groups are free to rotate, protons couple equivalently. In this circumstance, Eq. (11) approximates to Eq. (12) which is comparable with the McConnell relationship, Eq. (1) (see Section II,A)... 

It is therefore emphasized that the McConnell relationship must be... 

The general trend found earlier for the aromatic hydrogen hfcc values is confirmed, namely a(H4) > a(H2) > (FIs). In view of the empirical McConnell relationship, the spin population on the adjacent carbon atoms could be taken to be proportional to the hfcc values of hydrogen atoms bound to them. Thus, the experimental hfcc values of phenoxyl radical show much larger spin density on the para and ortho carbons ppara/Ponho = 1-5) than on the meta carbon (Ppara Pmeta = 5.3). While calculations are able to account for the ratio of para and ortho carbons, the trend for the meta carbon spin densities is not consistent with that suggested by the McConnell relationship. 

Discussion of Q-values of McConnell relationship. Theoretical discussion of total splitting. 

Subsequent geomorphic studies and work related to bauxite exploration have produced better dating and descriptions of relationships among erosion surfaces in South America (Aleva, 1979, 1984 Krook, 1979 McConnell, 1968 Menendez and Sarmentearo, 1984 Zorme-veld, 1969). The most economic bauxite deposits occur on the Neogene (55 Myr) surfaces. 

There is a relationship (the McConnell equation) between the unpaired electron density on a given atom and the polarization interaction with each attached proton ... 

McConnell (74) has shown that for the case of aromatic radical species where the interaction is between a spin density localized on a ptr orbital of a carbon atom and the proton bonded to that carbon atom a relationship exists between an observed proton contact interaction constant a, and the spin density p, on the adjacent carbon atom. This relationship is... 

The McConnell equation (Equation 1.17) shows the relationship of the observed coupling constant (aH) to the unpaired spin population on the adjacent carbon atom (pc)-... 

The spin density (pi) at the unsubstituted end of the radical can be calculated directly from the proton hyperfine coupling constants, using the relationship, A = 2i-lp (McConnell and Chesnut, 1958 Fessenden and Schuler, 1963). The spin density (ps) at the substituted end of the radicals can be calculated if it is assumed that the total spin density in the conjugated 77-electron system of the radical is unaffected by substitution. Then ... 

McConnell KP, Jager RM, Bland KI, et al. 1980. The relationship of dietary selenium and breast cancer. J Surg Oncol 15 67-70. 

The McConnell equation (Equation 1.18) expresses the relationship of the observed coupling constant (an) to the unpaired spin population on the adjacent carbon atom (pc) The constant Q is different from one situation to another, but when an electron in a pz orbital on a trigonal carbon atom couples to an adjacent hydrogen, it is about -24 G. Applied to aromatic hydrocarbons, where it is particularly easy to generate radical cations and anions, there proves to be a good correlation between coupling constants and the calculated coefficients in the HOMO and LUMO, respectively.62... 

McConnell D (1952) The Crystal ehemistiy of eaibonate apatites and their relationship to the composition of calcified tissues. J Dental Res 31 53-63... 

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