Substituent effect aniline

The reactivities of compounds of type 6 with aniline in acetone correlate quite well with substituent effects, and autocatalysis is unimportant here. In the less polar tetrahydrofuran, where the hydrochloride is only partly soluble, the reaction shows autocatalysis when aniline and -chloro aniline are reactants but not when the more basic -toluidine is involved. In these cases the solubility of the acidic product may also influence the differential behavior observed. 

In spite of the potential complexity of the general problem, even when restricted to the reagent family of amines, the nucleophilicities of such series as meta- and pom-substituted pyridines and anilines appear to correlate very closely with the expected substituent effects and with the basicities. This has been verified in the following cases (i) The reaction of pyridines (R = H, m- andp-CHs) with 2-chloro-3-nitro-, 2-chloro-5-nitro-, and 4-chloro-3-nitro-pyridines. ... 

In the case of 2,6-dimethylanilines (Table 7), although the chemical shifts for corresponding para substituents are at somewhat higher shielding than those of para substituents of aniline, owing to the shielding effect of the ortho methyl groups, the... 

The similarity observed for the correlation of the carbon shifts para to the substituent for 1 and 2 indicates that the nitrogen shift is a better probe of the transmission of the substituent effect to nitrogen. This conclusion can also be reached from a study of the polyfluorinated anilines. 

A study39 of substituent effects on the 15N chemical shift (515N) (Table 10) for 4-substituted anilines in DMSO was interpreted in terms of substituent solvation-assisted resonance (SSAR) effects. Solvation of certain conjugated jr-electron-acceplor (+R) substituents has been found to give significant enhancements in the acidities of anilines, phenols and other acids40,41, and the magnitudes of these enhancements increase with... 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

The terms 3 and E, indicate hydrophobic and steric effects specific to m-substituents. Eq. 10 describes substituent effects on the rate of transfer of substituted anilines catalyzed by carp vicera thiaminase 11... 

Let us now compare the pKa values (in AN) of the cation radicals derived from aniline, V-methylaniline, and. V-phenylaniline 5.5, 4.2, and 1.8, respectively (Jonsson et al. 1996). An additional N-methyl substituent produces only a marginal effect on the pKa of the aniline cation radical. At the same time, the effect of a single N-phenyl substituent in aniline is considerable. The phenyl-group effect on the aniline cation radical acidylation is predictable. 

Both aromatic and aliphatic amines react with butadiene to give tertiary octadienylamines 143 [51]. Amines with higher basicity show higher reactivity, and electron-donating substituents on aniline have an accelerating effect [68],... 

Table 2.8 Comparison of Different Models for Estimating the Substituent Effect in Aniline (Adapted from Murrell, 1963)...

In general, the substituent effects on the BDEs of anilines follow the usual trends observed for aromatic compounds, in line with the Brown-Okamoto <7+ constants190,197. 

The nucleophilic substitution reactions of anilines with ero-2-norbomyl arenesulfonates, 2, present an interesting example of the preassociation mechanism55 (Scheme 1). The rate is faster with 2-exo (k2 = 15.9 x 10 4 and 3.24 x 10-5 M 1 s 1 when X = Z = H in MeOH and MeCN at 60.0 °C, respectively) than with 2-endo (k2 = 0.552 x 10 5 M 1 s 1 with X = Z = H in MeOH at 60.0 °C). These reactions are characterized by a large pz (1.8 and 1.2 for 2-exo and 2-endo) coupled with a small magnitude of px (—0.21 and —0.15 for 2-exo and 2-endo). The pz values for the aniline reactions are even larger than those for the SY 1 solvolysis in MeOH (pz =1.5 and 1.0 for solvolysis of 2-exo and 2-endo). Thus the abnormal substituent effect in the anilinolysis of 2 can only be accounted for by the preassociation mechanism of Scheme 1. The upper route is the normal S/v 1 pathway, and the lower route is the preassociation pathway. The preassociation step, Xass, and association of the Nu to the ion pairs, kn. occur in a diffusion limited or fast process and k is the rate-limiting step. This mechanism leads to second-order kinetics and therefore is an SY/2 process, but structural effects on rates are very similar to those of S l reactions, since the R+ Z pair consists essentially of the two free ions. 

Like the case of phenols121,122, substituent effects on the proton dissociation of anilinium ions are strongly position-dependent. Examples have been provided by 3- vs 4-cyanoaniline and 3- vs 4-methoxyaniline123. Whereas the cyano substitution at the met a position of aniline increases the proton dissociation rate by as much as ca 29-fold, the rate is reduced by less than 3 times for 4-cyanoaniline vs aniline. In the case of the methoxy substituent, substitution at the met a position largely reduces the rate by ca 200-fold, but almost no effect was observed when it is at the para position. 

A series of /V-salicylidene-2,6-dialky Ian ilines (84a-84e, 85a-85d, 86a-86d, 87a, 87d, 88a, 88b, 88d, 89a, 89d, 90a, 90b and 90d) has been investigated in order to evaluate the alkyl substituent effects on the crystal packing of molecules and, in turn, their photochromic properties in the solid state178. The alkyl groups, particularly the isopropyl group, at the 2,6-positions of the aniline ring can lead to a nonplanar molecular structure, which is effective for the crystals to exhibit photochromism. 

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