o‐nitroaniline derivatives. IV—The mass spectra of o‐nitroanils

Abstract

Abstract-The principal feature of the mass spectra of o-nitroanils, ArCH=NC,H,NO,(o-), is an intense peak corresponding to the [ArCO]+ ion; this implies oxygen transfer from the nitro group to the azomethine carbon during the fragmentation process. In this series of anils, loss of OH from the molecular ion is not apparently an important fragmentation pathway, in contrast to the fragmentation of o-nitrobenzylideneanilines. Benzylideneaniline derivatives with an o-nitro substituent in both rings have mass spectra which indicate interaction of both nitro groups with the -CH=N-group, but in this series of spectra the [M -17]+ ion is again of low intensity.IT IS now well known that the mass spectra of o-disubstituted benzene derivatives frequently differ significantly from those of their m-and p-analogues, by virtue of interaction between the two o-substituents., Such 'ortho-effects' are particularly well documented for simple o-substituted nitro benzene^^*^ and several types of effect have been recognised: (i) hydrogen transfer from the a-or ,&position of the osubstituent to a nitro group oxygen; this may be followed, as in the case of o-nitrotoluene or o-nitroaniline, by the loss of a hydroxyl radical, or by further rearrangement and subsequent loss of a small molecule (e. The mass spectra of N-benzylideneaniline and some of its derivatives have been studied by Elias and Gillis6 and by Bowie et al. ' The simple anils undergo fragmentation as shown in Scheme l ; the spectra show a prominent molecular ion and fragment ions (a) and (b), corresponding to loss of hydrogen and the amine-derived aryl group, and (c), corresponding to that same aryl group. A low intensity ion, formed from (a) by loss of HCN and H, has been assigned7 the biphenylene structure (d).In the mass spectrum of N-o-nitrobenzylideneaniline ( Fig. 1 : cf. Ref. 7), however, an ortho-effect of type (i) comes into play; the ion (a) is insignificant, and both the molecular ion and the fragment (b) are reduced in intensity. The main fragmentation pathways involve loss of OH from the molecular ion followed either by loss of CN,O or successive loss of NO and HCN,' and the [M -17]+ ion has been formulated2 as (e) (Scheme 2). Examination of the mass spectra of a series of analogous anils (Table 1) reveals similar trends throughout the series.

Investigation of 4-(Nitrophenylamino)Pent-3-En-2-Ones and 4-(Nitrobenzylamino)Pent-3-en-2-Ones by Electron Ionization Mass Spectrometry. Observation of Characteristic Ortho Effects

“…In the case of tautomer b, the transfer of an oxygen atom to a neighbouring double bond has to take place, in a manner similar to that observed for other kinds of compounds containing a double bond ortho to the nitro group. [28][29][30] This can lead to the loss of a formyl radical, again as reported for compounds in which a double bond is ortho to the nitro group. 29,30 The loss of a ketene molecule (H 2 C=C=O) most likely proceeds via a McLafferty rearrangement.…”

o‐Nitrobenzylidene compounds. I—Competitive ortho interactions in the mass spectra of n‐o‐nitrobenzylidene‐o‐substituted anilines

“…In a previous paper, 5 we have shown that, although other simple anils of the general formula 1 also undergo primary fragmentation of the type illustrated, this 'normal' fragmentation process may be suppressed, in some cases almost entirely, by other competing ortho interactions. In the mass spectrum of N-o-nitrobenzylidene-0-nitroaniline (2j it is the nitro group in the amine-derived ring which interacts preferentially with the CH=N group, by transferring oxygen to the benzylidene carbon: this leads to the formation of an o-nitrobenzoyl ion (Scheme 2, pathway A).…”