Fluorinated methyl cation (CF3+, CFH2+)-alkyl nitrile cluster ions

Abstract

Ion-molecule reactions of CF(3)(+) or CFH(2)(+) with an acetonitrile-butyronitrile mixture yield product cluster ions in which the two neutral molecules are associated with the cation. The structures of the ion-molecule product ions were investigated by collision-induced dissociation in a multi-quadrupole mass spectrometer. The cluster ions fragment by loss of one neutral alkyl nitrile. The abundance of the fragment ions shows an unexpected inverse correlation with the proton affinity of the alkyl nitrile. This result is inconsistent with the formation of a simple cation-bound dimeric cluster containing two alkyl nitrile molecules and a fluorinated methyl cation; instead, a pair of non-symmetrical dimeric complexes, separated by a large internal barrier, is indicated. This result is analogous to that observed for the putative methyl cation-bound heterodimer of acetonitrile and butyronitrile. Collision energy dependence studies and ab initio calculations suggest that the dimeric complexes are formed in potential energy wells located in an approximately symmetrical potential energy surface. Quasi-equilibrium theory calculations were used in order to obtain additional insights into the experimental data.

Intrinsic Reactivity of Gaseous Halocarbocations toward Model Aromatic Compounds

“…The dilute gas-phase environment of mass spectrometers, in which a great variety of long-lived gaseous ions can be formed and isolated, has been used to conveniently measure many intrinsic kinetic isotope effects. [29][30][31][32][33][34][35] The isotope-mixed gaseous ions + CH 35 Cl 37 Cl and + CH 79 Br 81 Br give us the opportunity to measure the kinetic effect of [Ar-CHX] + functionalization. In reactions of + CH 35 Cl 37 Cl (Figure 5a), the [Ar-CH 37 Cl] + functionalization of benzene (m/z 127) is found to be slightly more favored than the [Ar-CH 35 Cl] + functionalization (m/z 125).…”

“…[29][30][31][32][33][34][35] The isotope-mixed gaseous ions + CH 35 Cl 37 Cl and + CH 79 Br 81 Br give us the opportunity to measure the kinetic effect of [Ar-CHX] + functionalization. In reactions of + CH 35 Cl 37 Cl (Figure 5a), the [Ar-CH 37 Cl] + functionalization of benzene (m/z 127) is found to be slightly more favored than the [Ar-CH 35 Cl] + functionalization (m/z 125). Hence, the H 35 Cl loss from the intact adduct is slightly faster than the H 37 Cl loss, which characterizes a normal kinetic isotope effect (K i ) 1.025).…”

“…In reactions of + CH 35 Cl 37 Cl (Figure 5a), the [Ar-CH 37 Cl] + functionalization of benzene (m/z 127) is found to be slightly more favored than the [Ar-CH 35 Cl] + functionalization (m/z 125). Hence, the H 35 Cl loss from the intact adduct is slightly faster than the H 37 Cl loss, which characterizes a normal kinetic isotope effect (K i ) 1.025). [Ar-CHBr] + functionalization of benzene by + CH 79 Br 81 Br also shows a normal isotopic effect as the product ion [Ar-CH 81 Br] + of m/z 171 (H 79 Br loss) is slightly favored over [Ar-CH 79 Br] + of m/z 169 (H 81 Br loss) (K i ) 1.033) (data not shown).…”

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“…127 The results of several studies on S N 2 reactions within clusters were reported. [128][129][130] Dimeric ions composed of the alkyl nitriles, acetonitrile (CH 3 CN) and butyronitrile (C 3 H 7 CN), and the methyl cation (CH 3 + ) do not have weakly bound structures such as 51 and 52 which interconvert via S N 2 reactions, but rather consist of a methylated nitrile which is covalently bound to the second nitrile as shown in 53 and 54. 128 A similar situation holds for clusters formed from acetonitrile and butyronitrile, and the fluorinated methyl cations (CF 3 + , CFH 2 + ).…”

“…128 A similar situation holds for clusters formed from acetonitrile and butyronitrile, and the fluorinated methyl cations (CF 3 + , CFH 2 + ). 129 An S N 2 reaction has been observed when binary clusters composed of NF 3 and CH 3 Cl are allowed to interact with a monochromatized electron beam. 130 The nucleophile, F 2 is generated within an energy region around 2 eV by resonant dissociative electron attachment from the NF 3 component of the cluster and then undergoes the S N 2 reaction with the substrate.…”