Carbon intramolecular fields

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). 

Sc, carbon chemical shift, referred to tetramethylsilane (8 = 0) (cf. Sect. I) SCS, substituent-induced chemical shift, or substituent effect difference between S s of a given carbon atom in a monosubstituted and the respective unsubstituted parent molecule (cf. Sect. Ill) NAE, nonadditivity effect nonadditivity of individual SCSs in disubstituted molecules (cf. Sect. IV) ICS, intramolecular-interaction chemical shift = NAE (cf. Sect. IV) A, polarization effect difference in S s of sp2 carbon atoms in a double bond (cf. Sect. IV-C) LEF, linear electric field (cf. Sect. II-B-3) SEF, square electric field (cf. Sect. II-B-3). 

As indicated, the reduction of an electron-deficient alkene renders a formally electropositive carbon center nucleophilic. The fields of electrohydrodimerization and electrohydrocyclization are a direct consequence of this realization [1, 2]. The former corresponds to the dimerization of an electron-deficient alkene via a process that couples the electron-deficient -carbons of the substrate. Overall, two electrons and two protons are consumed. Electrohydrocyclization is the intramolecular counterpart of this process. 

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." ... 

Dissociation of the carboxy proton causes deshieldings decreasing from the carboxy (4.7 ppm) to the y carbon (0.6 ppm) [305, 307] which are attributed to electric fields (Section 3.1.4.3). Intramolecular electric fields are also made responsible for the different sp2 carbon shifts in long-chain carboxylic acids [309]. 

Intramolecular and intermolecular interactions between C—H groups and the 71 system135 of carbon double bonds of olefins and of aromatic rings are of interest in the fields of molecular recognition and inclusion complexes in both organic chemistry and biochemistry. 

Natural products have always been attractive targets for the application of newly developed synthetic strategies. In this field, only a few examples have been reported, in which intramolecular aryl radical addition reactions occur to non-activated carbon-carbon double bonds [69]. One of the early examples is the first total synthesis of (—)-y-lycorane [70]. More recently, formal total syntheses of aspidos-permidine [71] and vindoline [72] have been accomplished by an aryl radical... 

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