Mass spectrometry studies of nitrene anions.

Nitrene anions are a class of reactive intermediates that provide a means for studying the corresponding neutral molecules via electron photodetachment spectroscopy and photoelectron spectroscopy. The added electron makes it possible for protected nitrene anions to be manipulated by external electric and magnetic fields of a mass spectrometer. Nitrene anions also display their own unique reactivities as reagents, which have been investigated using ion/molecule reactions. Mass spectrometry of negative ions has thereby provided information on the electronic states, reactivities, and thermochemical properties of nitrene intermediates. This review also includes a discussion of condensed-phase nitrene anions.

Probing the Pyrolysis of Guaiacol and Dimethoxybenzenes Using Collision-Induced Dissociation Charge-Remote Fragmentation Mass Spectrometry.

The dissociation of lignin model compounds has been examined using mass spectrometry and collision-induced dissociation charge-remote fragmentation (CID-CRF). The model compounds guaiacol and o- and m-dimethoxybenzene containing a remote sulfonate (SO3-) charge group undergo CID by dissociation without the involvement of the anionic group. The first dissociation for all three compounds is loss of methyl radical to form phenoxy radicals. Subsequent dissociation pathways depend on the specific structures being examined The dissociation pathways are compared to those observed upon gas-phase pyrolysis that have been reported previously. While the pathways are largely similar, there are some important differences that are explained by changes in dissociation barriers due to the effect of adding the charged group. This work shows that CID-CRF is an effective approach for tracking the thermolysis of lignin model compounds while eliminating secondary reactions that normally convolute such studies.

Investigation of the Substituent Effects of the Azide Functional Group Using the Gas-Phase Acidities of 3- and 4-Azidophenols.

The electronic effect of the azide functional group on an aromatic system has been investigated using Hammett-Taft parameters obtained from the effect of azide substitution on the gas-phase acidity of phenol. Gas-phase acidities of 3- and 4-azidophenol have been measured using mass spectrometry and the kinetic method and found to be 340.8 ± 2.2 and 340.3 ± 2.0 kcal/mol, respectively. The relative electronic effects of the azide substituent on an aromatic system have been measured using Hammett-Taft parameters. The σF and σR values are determined to be 0.38 and 0.02, respectively, consistent with predictions based on electronic structure calculations. The values of σF and σR demonstrate that azide acts as an inductively withdrawing group but has negligible resonance contribution on the phenol. In contrast, acidity values calculated for azide-substituted benzoic acids give values of σF = 0.69 and σR = -0.39, indicating that the azide is a strong π donor, comparable to that of a hydroxyl group. The difference is explained as being the result of "chimeric", or, alternatively, "chameleonic" electronic behavior of the azide, similar to that observed previously for the N-oxide moiety, which can be more or less resonance donating in response to the environment.