Gas-Phase Basicities and Acidities of Ethyl-, Vinyl-, and Ethynylarsine. An Experimental and Theoretical Study

Abstract

The gas-phase basicities and acidities of ethynyl-, vinyl- (or ethenyl-), and ethylarsine have been measured by means of FT-ICR techniques. The structures of the different neutral, protonated, and deprotonated species were elucidated by means of ab initio molecular orbital calculations at the MP2 level. Their final energies were calculated in the framework of the G2 theory. The agreement between calculated and experimental values for both basicities and acidities was fairly good. Protonation of vinylarsine and ethynylarsine at the Cα carbon leads to the breaking of the C−As bond, such that the corresponding protonated species can be viewed as complexes between ethylene and acetylene, respectively, with a AsH2 + cation. More importantly, these complexes are predicted to be as stable as the cations formed by direct protonation at the arsenic atom. For the particular case of ethynylarsine, this result is consistent with the experimental evidence. The gas-phase basicity decreases (GB values decrease) and acidity increases (Δacid G° values decrease) in the following order: ethylarsine, vinylarsine, ethynylarsine. The performance of the B3LYP density functional approach in the description of the thermochemical properties of these arsenic-containing species was also studied.

α,β‐Unsaturated and Saturated Derivatives of Be, Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

“…In general, the unsaturated compounds are stronger acids than the saturated ones, which is similar to that observed for similar systems that contain heteroatoms from groups 14, 15, and 16. [30][31][32][33]48] Nevertheless, these acidity enhancements are rather small in all cases. This is so because the XÀH (X= Mg, Ca) bond dissociation enthalpies do not change significantly from the saturated to the unsaturated derivatives, as illustrated by the near-constancy of the electron density at the corresponding bond critical point (see Figure 2).…”

“…In our group, we have devoted some effort to establishing and analyzing the acidity trends of heterocompounds. The main conclusions of these studies were that a,b-unsaturated amines, phosphines, [30] arsines, [31] stibines, [32] silanes, germanes, stannanes, [33] thiols, selenols, and tellurols [32] exhibit enhanced acidity compared with the corresponding saturated derivatives. In addition, for derivatives that contain heteroatoms from groups 14-16, this acidity enhancement depends mainly on the nature of the unsaturated moiety and on the heteroatom, which is mirrored in the existence of good linear correlations between the gas-phase acidities of homologous compounds of these three groups.…”

“…As expected, in saturated and a,b-unsaturated derivatives that contain substituents from groups 14, 15, and 16, deprotonation preferentially takes place at the hetero-A C H T U N G T R E N N U N G atom. [30][31][32][33] The situation can be significantly different, however, if the heteroatom is Be, Mg, or Ca, the XH bonds of which present a X d + À H dÀ polarity. Herein, we aim to address these questions by investigating the acidities of the three hydrides BeH 2 , MgH 2 , and CaH 2 , and also of the derivatives shown in Scheme 1, through the use of high-level density functional theory (DFT) and ab initio calculations.…”

Acidity Trends in α,β‐Unsaturated Sulfur, Selenium, and Tellurium Derivatives: Comparison with C‐, Si‐, Ge‐, Sn‐, N‐, P‐, As‐, and Sb‐Containing Analogues

“…Since the publication of this article, we have demonstrated on experimental (Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry) and theoretical grounds that such an increase of acidity also occurs for amines, phosphines, arsines, [2,3] silanes, germanes, and stannanes. [4] However, based on these results we cannot conclude that this increase of acidity does exist for any primary a,b-unsaturated derivatives of any element of the columns 2-16 of the periodic table.…”

Evaluation of the Enthalpy of Formation, Proton Affinity, and Gas-Phase Basicity of γ-Butyrolactone and 2-Pyrrolidinone by Isodesmic Reactions

“…14 However, the results obtained by using these two approaches are not very exact when compared to isodesmic/homodesmic reactions. 15,16 Thus, some methods aimed at the obtention of accurate thermochemical parameters have been developed in recent years. Among these methods are basis set extrapolation, multicoefficient methods, and composite chemical models.…”