Gas‐phase basicities of polyfunctional molecules. Part 1: Theory and methods

Abstract

The experimental and theoretical methods of determination of gas-phase basicities, proton affinities and protonation entropies are presented in a tutorial form. Particularities and limitations of these methods when applied to polyfunctional molecules are emphasized. Structural effects during the protonation process in the gas-phase and their consequences on the corresponding thermochemistry are reviewed and classified. The role of the nature of the basic site (protonation on non-bonded electron pairs or on p-electron systems) and of substituent effects (electrostatic and resonance) are first examined. Then, linear correlations observed between gas-phase basicities and ionization energies or substituent constants are recalled. Hydrogen bonding plays a special part in proton transfer reactions and in the protonation characteristics of polyfunctional molecules. A survey of the main properties of intermolecular and intramolecular hydrogen bonding in both neutral and protonated species is proposed. Consequences on the protonation thermochemistry, particularly of polyfunctional molecules are discussed. Finally, chemical reactions which may potentially occur inside protonated clusters during the measurement of gas-phase basicities or inside a protonated polyfunctional molecule is examined. Examples of bond dissociations with hydride or alkyl migrations, proton transport catalysis, tautomerization, cyclization, ring opening and nucleophilic substitution are presented to illustrate the potentially complex chemistry that may accompany the protonation of polyfunctional molecules. # 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:775-835, 2007

Insights into amine-based CO2 capture: an ab initio self-consistent reaction field investigation

“…We observe that the cyclized structures of MEA and EN are preferred over their extended counterparts in the gas phase. Studies by Bouchoux [30] and Karpas [31] have confirmed the importance of hydrogen bonding in polyfunctional molecules when calculating gas phase basicities and proton affinities.…”

Intrinsic (gas-phase) acidity and basicity of paracetamol

“…The extended kinetic method (EKM) [6][7][8][9][10][11][12][13][14] is an improved version of the simple Cooks kinetic method [17][18][19][20] which takes into account entropic effects on the competitive dissociations of a massselected proton-bound heterodimer (cluster-) anions [A·H·Aref(i)]…”

“…For this purpose, experiments were done using a triple-quadrupole mass spectrometer equipped with an electrospray source (ESI). The data were treated by the extended kinetic method (EKM) [6][7][8][9][10][11][12][13][14] which provide the deprotonation and protonation thermodynamic quantities associated with the general reactions (1) and (2), respectively.…”

Use of the HS-PTR-MS for online measurements of pyrethroids during indoor insecticide treatments

“…Accordingly, fluoroaromatic rings, alcynes, and alkenes have proton affinities around 750 kJ mol −1 , while protonation at the oxygen of a carbonyl group corresponds to PA close to 900 kJ mol −1 [26]. Since calculation at the G4MP2 level of the entire molecules (1)-(4) would be prohibitive in memory size and computational time, simplified model compounds (5)-(8) were considered (Fig.…”