Conjugation, effect electronegative

Are there any inductive effects (electronegative atoms or alkyl groups) that stabilize or destabilize any of the conjugate bases ... 

Third, substituents raising the effective electronegativity of boron will be expected to enhance B—C 7r-overlap (cf. 25a and 26). Finally, there can be competition between linear conjugation (36) and cross-conjugation (24). 

One of the prime examples of the extreme importance of conjugative effects is the case of XYC=Z molecules. As Z becomes more electronegative, the following trends are expected ... 

Lastly, relevant routine discussions for the elucidation of electronegativity or conjugation effects from 31P chemical data are fairly numerous ubbs. 1966, e to 9 1967, a, n to 14 1968,9 to 12 1969, is> Cyano.) phenyl... 

Miroshnichenko et al.380 have also shown that the frequency of the NH stretching vibration depends on the number of substituents and their electronegativity and that the effect is greater from the Deposition than the -position. However, it appears that under certain circumstances the substituent effects are not additive. Deviations of up to 7 cm-1 from the calculated value have been observed166,166,166a when steric interaction between substituents do not allow them to exert their full conjugative effect. 

We are left with the problem of substituent effects that do not depend on direct mesomeric interactions between the substituent and the reaction center. Effects of this kind can arise in one of two ways. First, the bond between the substituent and the substrate may be polar, and there may also be polar bonds or charged atoms in the substituent itself the charges set up in this way can influence the reaction center either by altering the effective electronegativity of atoms connected with it (inductive effect) or by direct electrostatic interaction across space (field effect). Secondly, the substituent may be attached to a conjugated system which does not itself take part in the reaction, the case exemplified by the Hammett equation (Eq. (105)) here it... 

It has been suggested that the C=0 stretching frequencies of acyl groups conjugated to porphyrin rings are useful probes of effective electronegativities of coordinated iron atoms in porphyrin complexes. These frequencies are also sensitive to... 

Conjugative effects enhance the acidity of certain hydrogens.292a when the proton on a C—H bond is on an atom bearing a substituent that can delocalize electron density toward a more electronegative atom, that proton is more acidic. The conjugate base (the carbanion) formed after its removal is more stable because the... 

A physical interpretation has been ascribed to each of the three terms in the MM2 torsional expansion from an analysis of ab initio calculations on simple fluorinated hydrocarbons. The first, onefold term corresponds to interactions between bond dipoles, which are due to differences in electronegativity between bonded atoms. The twofold term is due to the effects of hyperconjugation (in alkanes) and conjugation effects (in alkenes), which provide double bond character to the bond. The threefold term corresponds to steric interactions between the 1,4 atoms. It was found that the additional terms in the torsional potential were especially important for systems containing heteroatoms, such as the halogenated hydrocarbons and molecules containing CCOC and CCNC fragments. 

Acidity and basicity depend on the various factors that influence the position of the equilibrium between an acid HA and its conjugate base A. These include orbital effects, electronegativity, inductive effects, resonance effects, solvation hydrogen bonding, steric effects, and aromaticity. 

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