Methyl and Ethyl Cation Affinities of Rare Gas Atoms and N₂

Abstract

Gas-phase methyl cation affinities (MCAs) for rare gases Ne, Kr, and Xe were measured with a pulsed electron-beam high-pressure mass spectrometer. The MCAs for Ne and Kr were determined to be 1.2 ± 0.3 and 19.8 ± 2.0 kcal/mol, respectively, by the observation of the clustering reaction, CH3 + + Rg = CH3 +(Rg) (Rg = Ne and Kr). The MCA of Xe was measured to be 2.0 ± 0.6 kcal/mol larger than that of N2 by the observation of the substitution reaction CH3 +(N2) + Xe = CH3 +(Xe) + N2. Based on the MCA of N2 of 44.1 kcal/mol proposed by McMahon et al., the MCA of Xe is determined to be 46.1 ± 0.6 kcal/mol. Molecular orbital calculations at six different levels consistently gave almost identical MCA values for each of the rare gases. At QCISD(T)(full)/6-311++G(2df,p)//B3LYP/6-311++G(d,p), the calculated values (all in kcal/mol) are as follows: He, 0.6; Ne, 2.2; Ar, 15.9; Kr, 24.1; and N2, 43.2. For Xe at B3LYP/DZVP//B3LYP/DZVP, the calculated MCA is 39.0 kcal/mol. The ethyl cation affinities of Ar, Kr, and Xe were also measured. They are ∼1.7, 3.2 ± 0.3, and 6.8 ± 0.3, respectively. The stabilities of C2H5 +(Rg) and C2H5 +(N2) were discussed in terms of nonclassical (bridge) and classical (open) structures of C2H5 +.

OC199: Factors influencing success of conservative treatment of interstitial pregnancy

“…Only two minima, namely, 1 ⋅Ar( C 2 v ) and 1 ⋅Ar( C s ), were found (Figure 1), with binding energies of 6.5 and 3.9 kJ mol −1 , respectively. These values are consistent with the experimental binding enthalpy of approximately 7 kJ mol −1 measured for C 2 H 5 + ⋅Ar 16e. Significantly, these intermolecular Ar binding energies are well below the energy difference between 1 and 2 (ca.…”

Hypervalent versus Nonhypervalent Carbon in Noble‐Gas Complexes

“…[b] IRPD data from reference 4a. [c] Based on high‐pressure MS enthalpies of −1.2±0.3 and −19.8±2.0 kcal mol −1 from reference 4i with internal 298.15 K energy and Δ( pV ) corrections of +0.57 and 2.04 kcal mol −1 for CH 3 Ne + and CH 3 Ar + , respectively, from OLYP/TZ2P frequency calculations.…”

“…These ab initio relative energies again agree well with the available results from previous studies 4. High‐pressure mass spectrometric complexation enthalpies Δ H for reaction (4) of CH 3 Ne + and CH 3 Ar + are (−1.2±0.3) and (−19.8±2.0) kcal mol −1 , and that for reaction (5) of ArCH 3 Ar + is (−2.26±0.20) kcal mol −1 4b,i. For a more consistent comparison with our theoretical data, we have converted these experimental enthalpies into energies using 298 K internal energies and Δ( pV ) corrections based on OLYP/TZ2P frequency calculations.…”

Structures, energetics, and dynamics of gas phase ions studied by FTICR and HPMS

“…The bonding between a methyl cation and a base arises primarily from the interaction between the (r-HOMO of the base and the u-LUMO of the methyl cation; pi-effects are much less important (Deakyne & Meotner, 1990). Methyl cation affinities have also been reported in different studies using theoretical and experimental methods (Holtz, Beaucham, & Woodgate, 1970;Glukhovtsev et al, 1994;Maksic, Eckert-Maksic, & Knezevic, 1998;Cunje et al, 2004;Dixon et al, 2005;Wei et al, 2008).…”