Inductive effects, additivity

Typical ranges are 120-130 Hz for sp3,150-180 Hz for sp2 and ca. 250 Hz for carbons. In addition, inductive effects of a-positioned heteroatoms and groups, as well as ring strain, play important roles, as shown for substituted methanes (CH,X and CH4 nCln) and cycloalkanes. 

Calculations of vibrational frequencies are never accurate enough to verify that the secondary IE arises entirely from zero-point energies. Therefore although they do confirm a role for zero-point energies, which was never at issue, they cannot exclude the possibility of an additional inductive effect arising from changes of the average electron distribution in an anharmonic potential. The question then is whether it is necessary to invoke anharmonicity to account for a part of these secondary IEs. 

This is due to B-strain [272] rather than to any additional inductive effects from the alkyl chain as compared to a methyl group. 

Modern concepts of organic chemistry have provided interpretation and explanation for a variety of supposedly anomalous and unusual reactions of carbohydrate compounds. These concepts have often been derived from a study of relatively more simple substances in which there has been little complication resulting from interfering and conflicting factors. Consequently, direct application of these concepts to the more complex carbohydrate compounds without due consideration of alternative possibilities may result in oversimplification and a false picture. Despite such inherent hazards, it is believed that a useful purpose can be served by the correlation and discussion of the carbohydrate reactions with direct reference to analogous properties of simpler organic compounds. For this objective, we can define the acyclic forms of the aldoses as polyhydroxy-aldehydes, and their cyclic forms as polyhydroxy-cyclohemiacetals. In these compounds, besides the additive, inductive effect of the hydroxyl... 

The basic piSTa values, which have to be considered as equilibrium values, including those of anhydrous and hydrated species, reveal a destabilizing inductive effect of the 6- and 7-methyl group towards 3,4-hydrate formation, as do also the 2-methylamino and 2-dimethylamino groups for additional steric reasons. If the cation of 2-aminopteridine did not add water its value would be about 1.6, arrived at by substracting from the piSTa 2.6 of the essentially anhydrous 2-amino-4,7-dimethylpteridine cation 0.3 for the 7- and 0.7 for the 4-methyl group. The difference between the observed value of 4.29 and the... 

The observed acidities in the gas phase are interpreted in terms of the negative induction effect of the halo substituents however, the microscopic picture of the solvent effects in addition to such induction effects of the solute have not been clarified. 

According to Roberts et al. the direction of addition of ammonia to 3-substituted benzynes might be predicted by considering the amide ion to add so as to provide the most favorable location of the negative charge with respect to the inductive effect of the orienting substituent. Thus, ammonia adds to 3-methoxybenzyne (39) producing chiefly n-aminoanisole (40). 

Electrophilic substitution of a disubstituted benzene ring is governed by the same resonance and inductive effects that affect monosubstituted rings. The only difference is that it s now necessary to consider the additive effects of two different groups. Tn practice, this isn t as difficult as it sounds three rules are usually sufficient. 

In addition to pyridine, the six-membered diamine pyrimidine is also found commonly in biological molecules, particularly as a constituent of nucleic acids. With a pKa of 1.3, pyrimidine is substantially less basic than pyridine because of the inductive effect of the second nitrogen. 

The carbonyl group also possesses electrophilic properties at the carbon atom and nucleophilic properties at the oxygen atom. Nucleophilic attack of the carbonyl group is favored if this is attached to an aromatic ring (inductive effect) and there is also a methoxy or phenolic OH group present in the 4-position. Changing a neutral reaction medium by proton addition has the same effect. 

Fig. 2. Components of Li enthalpies of complexation with methylamines. Successive steps indicate the effect on energy of interaction between Li and the amine of inclusion of additional components of the binding energy. The diagram shows that the permanent dipoles on amines (the charge on the nitrogen of the isolated amine) favor ammonia over trimethylamine complexation, but that polarizability and inductive effects (shift of negative charge onto the nitrogen in the complex) cause a massive turnaround in favor of complexation with trimethylamine rather than ammonia. Of particular importance is the near inversion of order caused by the addition of repulsive van der Waals terms. Modified after Ref. (9).

The significance of B—C ir-bonding in determining the course and the ease of chemical reaction with organoboranes is obviously a more difficult question for both the experimentalist and the theoretician. Again, both inductive and resonance effects can, in principle, play a role but in addition, steric effects now become important, either for intramolecular reactions, as in Eq. (5), or for intermolecular reactions, as in Eqs. (7, 8). 

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