Light Absorption Studies: Part Xi Electronic Absorption Spectra of Nitrobenzenes

Abstract

ABSTllACTThe spectra of nitrobenzenes are discussed in terms of previously proposed hypotheses relating electrorlic interactions arld ultmviolet absorption spectra.

Light Absorption Studies: Part Xii. Ultraviolet Absorption Spectra of Benzaldehydes

“…This assignment may be questioned on the grounds that the benzaldehyde band is appreciably displaced and also because the band does not show the doublet characteristic of benzaldehyde absorption in inert media. Oil the other hand, a nitro-group normally gives rise t o appreciable changes in the spectra of meta-disubstituted benzene derivatives (5). Also, our assig~lmeilt receives support from the spectrum of m-nitrobenzaldehyde in ethanol (see Table IV).…”

“…because of the secondary short-range interaction of the non-formyl substituent (5,22). The second B-band correspo~lds to the absorption of the other substituent, with the formyl group acting as the secondary substituent.…”

Light Absorption Studies: Part Xiii. The Electronic Absorption Spectra of Ring-Substituted Anilines

“…As previously mentioned (18,19), two B-bands can frequently be discerned in the spectra of metadisubstituted benzene derivatives, and these B-bands have been associated with transitions involving the two monosubstituted parent compounds. In this way, the Can.…”

“…Structures, which may be crudely represented by resonance forms of of type IV, would again contribute t o the electronic excited state, and these resonance forms, by analogy with the previously discussed resonance structures of that type (18). would be expected t o be favored by an electron-withdrawing substituent in the meta position.…”

“…I t may be noted that for these examples the maximal extinction coefficient (E,,,) is frequently reduced relative t o aniline, whereas in disubstituted benzene derivatives, when the substituents are electron withdrawing, the values of E, , , are usuall~-iwcreased relative to the monosubstituted parent con~pound (cf. 17,18,19). Table I1 also shows that parasubstitution usually displaces the B-band of aniline towards longer wavelength.…”