Arylamine resonance

The orbital and resonance models for bonding in arylamines are simply alternative ways of describing the same phenomenon Delocalization of the nitrogen lone pair decreases the electron density at nitrogen while increasing it m the rr system of the aro matic ring We ve already seen one chemical consequence of this m the high level of reactivity of aniline m electrophilic aromatic substitution reactions (Section 12 12) Other ways m which electron delocalization affects the properties of arylamines are described m later sections of this chapter... 

As noted previously, arylamines are generally less basic than alkylamines. Anilinium ion has pKa = 4.63, for instance, whereas methylammonium ion has pfCa = 10.64. Arylamines 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+. In resonance terms, aryl-amines are stabilized relative to alkylamines because of their five resonance forms. 

Much of the resonance stabilization is lost on protonation, however, so the energy difference between protonated and nonprotonated forms is higher for arvlamines than it is for alkylamines. As a result, arylamines are less basic. Figure 24.3 illustrates the difference. 

Figure 24.3 Arylamines have a larger positive AG for protonation and are therefore less basic than alkylarnines, primarily because of resonance stabilization of the ground state. Electrostatic potential maps show that lone-pair electron density is delocalized in the amine but the charge is localized in the corresponding ammonium ion.

Resolution (enantiomers), 307-309 Resonance, 43-47 acetate ion and, 43 acetone anion and. 45 acyl cations and, 558 allylic carbocations and, 488-489 allylic radical and, 341 arylamines and, 924 benzene and, 44. 521 benzylic carbocation and, 377 benzylic radical and, 578 carbonate ion and. 47 carboxylate ions and, 756-757 enolate ions and, 850 naphthalene and, 532 pentadienyl radical and. 48 phenoxide ions and, 605-606 Resonance effect, 562 Resonance forms, 43... 

From appraisal of their respective resonance stabilisation, arylnitrenium ions and alkoxynitrenium ions should form with similar facility. On account of the fact that A-acetoxy-A-acetyl arylamines 7 are penultimate carcinogens in the metabolism of aromatic amines, A-acyloxy-A-alkoxyamides 3 were designed to test their potential as DNA-damaging agents. 

Other low-molecular systems that have been investigated in waveguiding films are the guest-host system Alq3 DCM (see below for the emission in tme resonators), arylamines, and oligothiophenes. TPD (6) shows an emission peak in thin films at 418 nm when pumped with 35-ps pulses at 347 nm [185]. The... 

Arylamines are weaker bases than cyclohexylamines because of resonance. Aniline, a typical arylamine, exhibits the resonance structures shown in Figure 8-1. 

Resonance Effects on Basicity Arylamines (anilines and their derivatives) are much weaker bases than simple aliphatic amines (Table 19-3). This reduced basicity is due to resonance delocalization of the nonbonding electrons in the free amine. Figure 19-5... 

Peroxide decomposers, which promote the conversion of peroxides to non-free radical products, presumably by a polar mechanism. Examples are dialkylarylphosphites, dialkylthiodipropionates or long chain alkylmercaptans. Free radical chain stoppers or "radical traps," which interact with chain-propagating RO2 radicals to form inactive products. This is usually accomplished by its donation of an H radical to terminate an active polymer radical, itself forming a more stable one (usually by resonance) which will not rereact with the polymer (e.g., with the help of steric hindrance) and will eventually relax its energy through thermalization, fluorescence or other innocuous means. Examples are sterically hindered phenols or secondary arylamines. 

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