Electronegative groups, definition

There is little information for fluoro-substituted sulfinyl groups. Values of a and ffp for SOCFj based on benzoic acid ionization are 0.63 and 0.69 respectively , compared with values of about 0.52 and 0.49 for SOMe (Table 3). Thus the electronegative fluorine somewhat enhances the electron-attracting influence of the sulfinyl function and makes the order more definitely sulfur lone pair to engage in 7t(pp) conjugation. Values of and ffp for SOCF3 based on anilinium ion dissociation are 0.76 and 1.05 respectively . An increase of 0.13 as between and [Pg.509]

Zintl phases remarks on their definition. We have seen that the Zintl phases may be considered as a group of compounds formed by an electropositive (cationic) component (alkali, alkaline earth metal, lanthanide) and an anionic component (for instance a main group element of moderate electronegativity). The anionic part of the structure may be described in terms of normal valence combination. 

Nevertheless, there is a definite trend in H 0 bond lengths consistent with the relative electronegativities of the donor and acceptor groups. 

Successful model building is at the very heart of modern science. It has been most successful in physics but, with the advent of quantum mechanics, great inroads have been made in the modelling of various chemical properties and phenomena as well, even though it may be difficult, if not impossible, to provide a precise definition of certain qualitative chemical concepts, often very useful ones, such as electronegativity, aromaticity and the like. Nonetheless, all successful models are invariably based on the atomic hypothesis and quantum mechanics. The majority, be they of the ah initio or semiempirical type, is defined via an appropriate non-relativistic, Born-Oppenheimer electronic Hamiltonian on some finite-dimensional subspace of the pertinent Hilbert or Fock space. Consequently, they are most appropriately expressed in terms of the second quantization formalism, or even unitary group formalism (see, e.g. [33]). 

Components of Zintl phases are metals A (Li-Cs, Mg-Ba) and semimetals X (B-Tl, Si-Pb, P-Bi, Te). The definition of the components of Zintl phases is not quite sharp, neither for the metals nor for the semimetals, until today. While the alkali- and alkaline earth metals are undoubtedly metals in the classical sense, there is still the vast field of transition metals T, which in Zintl type compoimds, might also occur. Electropositive T atoms may replace the main group metal A and electronegative ones tike a semimetal X. One of the wellknown examples here is CsAu (a diamagnetic semiconductor). This phase shows the typical properties of a valence compound according to the electron transfer description Cs Au [4]. 

The mixture probably contains the same trichloroethane as the peaks at 45.3 and 95.6 p.p.m. suggest (the chemical shifts of the mixture need not be quite the same as those of the pure compound as each compound is effectively dissolved in the other). The remaining peaks at 7.0, 27.3, 35.2, and 206.3 p.p.m. definitely belong to a carbonyl compound, probably a ketone since 206.3 p.p.m. is so large. Butanone fits the bill as it has one methyl and one CH2 group on the carbonyl group and one methyl away from any electronegative atoms. There are other possibilities. 

Using group electronegativities as local invariants electronegativity-based connectivity indices were proposed as molecular descriptors. Atomic electronegativities are also used in the definition of MARCH-INSIDE descriptors. 

---