Gas‐phase basicities of polyfunctional molecules. Part 2: Saturated basic sites

Abstract

The present article is the second part of a general overview of the gas-phase protonation thermochemistry of polyfunctional molecules. The first part of the review (Mass Spectrom. Rev., 2007, 26:775-835) was devoted to the description of the physico-chemical concepts and of the methods of determination, both experimental and theoretical, of gas-phase basicity. Several clues concerning the structural and energetic aspects of the protonation of isolated species have been emphasized. In the present article, specific examples are examined. The field of investigation is limited to molecules containing a "saturated" basic site, that is, nitrogen or oxygen atoms engaged in simple σ bonds with their neighboring. Aliphatic, cyclic and aromatic poly-amines, amino alcohols, alcohols, ethers, and hydroxyl-ethers, are successively presented.

Equatorial coordination of uranyl: Correlating ligand charge donation with the Oyl-U-Oyl asymmetric stretch frequency

“…The monodentate tmtu complex coordinates through the 8 thioketone S atom, while the bidentate complex is coordinated to uranium by both a thioketone S atom and a thioamide N atom. Because protons generally bind to one nucleophilic site in a molecule, 8 this unexpected bidentate coordination of tmtu to uranium is exemplary as to why PAs should not necessarily correlate well with MCAs when a second coordinating electron donor such as N is present in the ligand. The computed structure of UO 2 (tmtu) 4 …”

Formation of sugar radical cations from collision-induced dissociation of non-covalent complexes with S-nitroso thiyl radical precursors

“…A possible explanation based upon the labelling studies (Fig. 2c), which highlight that radical cation formation involves H atom abstraction followed by proton transfer, is that as the linker size increases, the proton affinity of H 2 NXSH is likely to increase (based on the proton affinities of related amine alcohols and diamines [21]), making proton transfer from H 3 NXSH + to the sugar radical, [M À H] , less likely. Finally, the fact that methyl mannopyranosides produce less of the radical cation than methyl galactopyranosides and methyl glucopyranosides highlights that the structure of the sugar also plays a role in the yield of [M ] + produced.…”

Toward extension of the gas-phase basicity scale by novel pyridine containing guanidines

“…The largest difference between the calculated and evaluated entropies in our case amounts to 22 J mol −1 K −1 (for base 12) indicating that neglecting the conformer mixing and hindered rotations could be the origin of the observed discrepancy between the calculated and experimental entropies of protonation. The errors in entropies are expected to have small impact on the measured GBs since the errors in entropies cancel out with the errors of the PA values [16,[29][30][31][32]. To test whether possible errors in the entropies cause significant deviations of the PAs we compared the measured GBs and PAs with the data calculated using several calculation approaches (see below).…”

“…[32,40,41] as the most recent ones. Besides being dependent on the level of theory, the accuracy of the calculated GB and PA values depends strongly on effectively and properly identifying the most stable neutral and protonated structures.…”

“…This was ascribed to the cancelation of errors in PAs and S p . For more detailed discussions about the applications and the accuracy of the kinetic methods in obtaining thermochemical data the reader is referred to the recently published review articles by Vékey, Armentrout and Bouchoux [16,27,30,31,32].…”