Resonance stabilization aniline

The gas-phase exothermicity is due to the enhanced resonance stabilization of aniline compared to benzene for the nonzwitterionic amino acids, as found in the gas phase. On the other hand, the aniline resonance stabilization is lost in the zwitterionic amino acids of the solid phase and thus the reaction is essentially thermoneutral. This is, of course, related to the weak basicity of aniline compared to related nonaromatic bases such as cyclohexylamine, as exhibited by the ca 50 kJ mol-1 exothermicity of the formal reaction 29. 

This resonance stabilization is lost when the amine group becomes protonated and o-cyanoaniline is therefore a weaker base than aniline... 

This is due to a resonance effect. Aniline is stabilized by sharing its nitrogen lone-pair electrons with the aromatic ring. In the anilinium ion, the resonance stabilization is dismpted by the proton bound to the lone pair. 

Direct connection of pendant heteroatom to polystyrene aryl is a synthetically more difficult, but often still feasible (37), alternative. However, though bonds from phenyl to many common heteroatoms are relatively strong, resonance stabilization of partial positive charge developed on an arylated atom activates it to leave other substituents alkyl anilium salts (12) and anilines (38), as well as phenolic esters (39), are relatively easy to cleave. Aryl linkages,... 

Because of the opposite nature of the n interactions between the ring and either the nitro or the amino substituent, let us assess the stabilization energies of nitrobenzene and aniline. In equation 13, the resonance stabilizing energy of aniline was defined as the exothermicity of a reaction involving arbitrary reference states. By analogy to equation 13, we may write equation 57 for nitrobenzene and the same arbitrary reference states, R = /-Pr or t-Bu. 

Basicity of aniline Aniline, like all other amines, is a basic compound ( Tb = 4.2 X 10 °). Anilinium ion has a = 4.63, whereas methylammo-nium ion has a pK = 10.66. Arylamines, e.g. aniline, are less basic than alkylamines, because the nitrogen lone pair electrons are delocalized by interaction with the aromatic ring tt electron system and are less available for bonding to H+. Arylamines are stabilized relative to alkylamines because of the five resonance structures as shown below. Resonance stabilization is lost on protonation, because only two resonance structures are possible for the arylammonium ion. 

Resonance stabilizes the free base relative to its protonated form, and the effect is greater with p-cyanoaniline than with aniline. 

Draw the important resonance structures for aniline. Use the curved arrow convention to show how the electrons are moved to create each new resonance structure. Discuss the relative contribution of each to the resonance hybrid and the overall resonance stabilization of the compound. 

Which is the stronger base, aniline or ammonia The same reasoning applies. Aniline is stabilized by resonance. The basic pair of electrons is delocalized into the ring and is less available to form a covalent bond, so it is a weaker base. (Of course, if the conjugate acid of aniline is stronger than ammonium ion, then aniline must be a weaker... 

Many of the ashless anti-knocks are amines or phenols [26] and are related to liquid-phase oxidation inhibitors. They probably work by reacting with active radicals (particularly OH) to produce radicals which are inert. For instance, N-methyl aniline (NMA) CeHsNHCHs probably produces stabilized CeHsNCHs radicals which, because of their resonance stabilization, are unable to react to regenerate active radicals again and may undergo only radical recombination reactions. The rate of radical removal by this process is likely to be limited in the most favourable case by how fast the additive can react with OH to produce stabilized radicals. Although exact rates are not known, this is probably already a fast process for NMA, and unlikely to be very much faster for any other substance. Indeed, the most effective ashless anti-knock found by MacKinven [26] in an extensive study of 970 substances was a tetra-aryl hydrazine, with a molar effectiveness 2.9 times that of NMA. 

Arylamines have a larger positive AG° for protonation and are therefore less basic than alkylamines, primarily because of resonance stabilization of their ground state. Electrostatic potential maps show that lone-pair electron density is delocalized in aniline compared to cyclohexylamine but that the corresponding ammonium ions localize charge in the same way. 

With aniline, however, the equilibrium is displaced to the left in comparison to cyclohexyl amine because resonance stabilizes the non-protonated molecule (LXI to LXIII) and not the anilinium ion (LXIV). 

Oximes which yield resonance-stabilized acinitroalkanes can be oxidized by the procedure used for oxidation of anilines and nitrosoamines. ... 

The introduction of additional hydroxy groups into the phenolic ring assists the development of a ketonic character because the energy released by formation of multiple keto groups compensates for the loss of resonance stabilization. There are many reports concerning the ability of polyhydric phenols to react as tautomeric keto forms. For instance, the conversion of phenol into aniline proceeds under very drastic conditions (350-450 °C, 50-60 bar) and the substitution of one hydroxy group in resorcinol by an amino group... 

Another type of proximity effect arises when the placement of a substituent interferes with the orbital overlap required for resonance stabilization. This can be seen clearly in the acidity of substituted benzoic acids and in the basicity of substituted anilines. 

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