Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp² nitrogen containing compounds

Abstract

This paper constitutes the fifth part of a general review of the gas-phase protonation thermochemistry of polyfunctional molecules (Part 1: Theory and methods, Mass Spectrom Rev 2007, 26:775-835, Part 2: Saturated basic sites, Mass Spectrom Rev 2012, 31:353-390, Part 3: Amino acids, Mass Spectrom Rev 2012, 31:391-435, Part 4: Carbonyl as basic site, Mass Spectrom Rev 2015, 34:493-534). This part is devoted to non-aromatic molecules characterized by a lone pair located on a sp nitrogen atom, it embraces functional groups such as imines, amidines, guanidines, diazenes, hydrazines, oximes, and phosphazenes. Specific examples are examined under five major chapters. In the first one, aliphatic and unsaturated (conjugated and cyclic) imines, hydrazones, and oximes are considered. A second chapter describes the protonation energetic of aliphatic, conjugated, or cyclic amidines. Guanidines, polyguanides, and biomolecules containing guanidine were examined in the third chapter. A fourth chapter describes the particular case of the phosphazene molecules. Finally, diazenes and azides were considered in the last chapter. Experimental data were re-evaluated according to the presently adopted basicity scale, i.e., PA(NH ) = 853.6 kJ/mol, GB (NH ) = 819 kJ/mol. Structural and energetic information given by G4MP2 quantum chemistry computations on typical systems are presented. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 37:139-170, 2018.

Push–Pull Effect on the Gas-Phase Basicity of Nitriles: Transmission of the Resonance Effects by Methylenecyclopropene and Cyclopropenimine π-Systems Substituted by Two Identical Strong Electron Donors

“…This choice does not imply a priori that the The cyclopropenimine (or cyclopropeneimine, less common name) skeleton (Z: N) has a special status among the heteroatomic analogs of methylenecyclopropene. It is present in many systems, which have been largely studied experimentally and theoretically, in particular in the last ten years, as platforms for developing superbases and organocatalysts [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The imino bond carrying a nitrile group on the nitrogen, >C=N−CN, is present in molecules of biological interest, in particular the neonicotinoids [35][36][37], and in materials developed for their electronic applications [38][39][40].…”

Gas phase basicities of polyfunctional molecules. Part 6: Cyanides and isocyanides

“…The third part is a survey of the present knowledge on the experimental and theoretical gas‐phase protonation thermochemistry of the 20 gaseous proteinogenic aminoacids. The fourth part was devoted to polyfunctional molecules bearing a carbonyl group as basic site and finale the fifth part is focused on the basicity properties of non aromatic molecules characterized by a lone pair located on a sp 2 nitrogen atom (ie, imines, amidines, guanidines, diazenes, hydrazines, oximes, and phosphazenes) . The present part is concerned with molecules containing sp hybridized nitrogen atoms, that is cyanides (nitriles) and isocyanides (isonitriles).…”

“…A number of molecules studied here include species characterized by large proton affinity and gas‐phase basicity values, due, in particular to the so‐called “push‐pull effect” where a π‐donnor subtituent is directly linked to the nitrile group . Accordingly, some of these molecules are denoted as “superbases,” that is are stronger bases than the classical proton sponge, 1,8‐bis(dimethylamino)naphthalene (see parts 2 and 5 of this review), which is characterized by a proton affinity (PA) of 1015 kJ/mol, and a gas‐phase basicity (GB) of 980 kJ/mol.…”

Evaluation and prevention of the negative matrix effect of terpenoids on pesticides in apples quantification by gas chromatography–tandem mass spectrometry

“…Most GB values for nitrogen compounds are available in the literature [50,51] but not for the targeted pesticides. It was observed that gas phase basicity increases from nitriles < amines < amides < pyroles < pyrimidines < pyridines.…”