Shielding, intramolecular

The behavior of the ort/io-methyl resonances of diarylsulfoxides is also exceptional (48). For example, both methyls of o-tolyl-p-tolylsulfoxide show nonequivalence of the same sense as that expected for the p-methyl group on the basis of the general sulfoxide model. The senses observed for o-methyl groups in several other o-tolyl-sulfoxides are also inverted, whereas those of other resonances are normal. This behavior, which may result from an intramolecular shielding of these groups by either sulfinyl or aromatic moieties in rotamers whose populations are affected by the CSA, is not well understood. 

Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

Recently it has been evidenced that a large aromatic substituent, such as naphtyl, can provide a intramolecular steric shielding for an a-keto ester moiety [9] resulting in enantio-... 

Of particular interest when considering ionizable compounds is the difference of lipophilicity between the neutral species and one of its ionic forms, because ionization dramatically alters intramolecular interactions (such as electronic conjugation, internal ionic and hydrogen bonds, polarity, hydrophilic folding, and shielding). In a given solvent system, diff (log is approximately constant for compounds with similar chemical... 

In nitrobenzene, for example, the intramolecular electric field of the nitro group increases the a electron densities at the ortho carbon nuclei, so reducing the electron density at the attached protons. This effect, in fact, overcompensates the effect of electron withdrawal by the nitro group, and a net shielding is observed (Table 5). 

For lariat ethers to be effective as polymer-bound phase transfer catalysts, sidearm and macroring cooperation must be intramolecular. It is unlikely that two lariat ethers will be close enough on a polymer backbone or other support for the ring of one compound to interact with the sidearm donors of another. The mechanical attributes of lariat ethers will be independent of spacing but for any advantage in cation binding and anion activation to be realized, the macroring and its attached sidearm must cooperate to envelop the cation, solvate it, and shield it from the counteranion. 

The intramolecular n-electron donation from the remote double bond to the stannylium ion center in the stannanorbornyl cation, 62 (8 Sn = 336 in CeDg), also leads to a significant shielded tin nucleus compared to what is expected for a free trialkylstannylium ion. As already shown for the sila compounds 55-58, the coordination of the C = C double bond to the electron-deficient tin center in 62 is indicated by a low-field shift of the resonance of the vinylic carbon atoms by 11.1 ppm. Additionally, the small scalar Sn-C coupling constant J(SnC) = 26 Hz gives clear evidence for the intramolecular Ti-complexation." ... 

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