System aniline-benzene

Weller24 has estimated enthalpies of exciplex formation from the energy separation vg, — i>5 ax of the molecular 0"-0 and exciplex fluorescence maximum using the appropriate form of Eq. (27) with ER assumed to have the value found for pyrene despite the doubtful validity of this approximation the values listed for AHa in Table VI are sufficiently low to permit exciplex dissociation during its radiative lifetime and the total emission spectrum of these systems may be expected to vary with temperature in the manner described above for one-component systems. This has recently been confirmed by Knibbe, Rehm, and Weller30 who obtain the enthalpies and entropies of photoassociation of the donor-acceptor pairs listed in Table XI. From a detailed analysis of the fluorescence decay curves for the perylene-diethyl-aniline system in benzene, Ware and Richter34 find that... 

DAAB is a respiratory tract, skin, and eye irritant. DAAB yields benzene and aniline as metabolites. The proposed metabolic pathway for DAAB is that it is cleaved reductively by liver enzymes or gut flora to form aniline, benzene, and nitrogen. DAAB metabolism also results in the formation of a reactive phenyl radical, which could account for an additional risk of toxicity or carcinogenicity. The erythrocyte and lymphoid systems are major targets of DAAB toxicity. Induction of lymphoid atrophy of the thymus and other lymphoid tissues were observed, as well as methemoglobin formation, accompanying anemia, increased spleen weights, and regenerative hematopoiesis. 

The same phenomenon is observed in substituted anilines. Anilines are usually much weaker bases than aliphatic amines because of resonance overlap of the nitrogen s lone pair of electrons with the pi system of benzene. When that resonance is disrupted, the aniline becomes closer in basicity to an aliphatic amine. (See problem 19-49(c).)... 

Several aromatic amines have special names that have also been approved for use by I.U.P.A.C. For example, the amine of benzene is given the name aniline. In the CA system, aniline is named benzenamine. 

Hematopoietic agents. Affect the blood system, including the blood-forming organs, leading to reduced blood functions and cyanosis, and loss of consciousness. Examples carbon monoxide, cyanides, aniline, benzene, arsenic, fluoride. 

This reaction sequence is much less prone to difficulties with isomerizations since the pyridine-like carbons of dipyrromethenes do not add protons. Yields are often low, however, since the intermediates do not survive the high temperatures. The more reactive, faster but less reliable system is certainly provided by the dipyrromethanes, in which the reactivity of the pyrrole units is comparable to activated benzene derivatives such as phenol or aniline. The situation is comparable with that found in peptide synthesis where the slow azide method gives cleaner products than the fast DCC-promoted condensations (see p. 234). 

A group with a more powerful (electron-withdrawing) inductive effect, e.g. NOa, is found to have rather more influence. Electron-withdrawal is intensified when the nitro group is in the o- or p-position, for the interaction of the unshared pair of the amino nitrogen with the delocalised it orbital system of the benzene nucleus is then enhanced. The neutral molecule is thus stabilised even further with respect to the cation, resulting in further weakening as a base. Thus the nitro-anilines are found to have related p a values ... 

Similarly, the affixment of conjugate substituents onto aromatic systems extends the conjugation of the latter and causes fluorescence maxima of the substituted derivatives to lie at wavelengths longer than those of the parent compound. Hence, the fluorescence of aniline lies at 340 nm while that of the parent hydrocarbon benzene lies at 262 nm. 

Aniline and phenoxide ion have strong UV absorptions due to the overlap of the lone pair on the nitrogen (or oxygen) with the 7r-system of the benzene ring. This may be expressed in the usual Valenee Bond terms ... 

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