Michael Meot-Ner

Reactions of CH3OCH+2 with nitrogen bases: a mechanism for the formation of protonated imines

Abstract The CH 3 OCH + 2 ion reacts with NH 3 and with primary and secondary amines R 2 NH with the elimination of CH 3 OH to form the protonated imines R 2 NCH + 2 . Proton transfer and methyl cation transfer, although exothermic, are not major channeles. Elimination of CH 3 OH is also observed with C 2 H 5 OH to form C 2 H 5 OCH + 2 . No reaction is observed with HCN, while methyl cation transfer to form CH 3 CNCH + 3 is the main channel with CH 3 CN. The reactivity of the CH 3 CHOH + isomer is different, with fast proton transfer to CH 3 CN and NH 3 . With CH 3 CH, a fast three-body association channel is also observed.

The proton affinity of cyanogen and ion/molecule reactions of C2N2+

Abstract The proton affinity of C 2 N 2 has been determined from proton transfer equilibria using forward and reverse rate coefficients from selected-ion flow tube measurements. The results yield a proton affinity for CH 3 Cl of 673±4 kJ mol −1 and a proton affinity for C 2 N 2 of 674±4 kJ mol −1 compared with a proton affinity for C 2 H 4 of 680±2 kJ mol −1 . The C 2 N 2 H + ion is also formed from the reactions of C 2 N + 2 ions with hydrogen and with H 2 O. In the latter, charge transfer competes with hydrogen atom transfer, while in the reaction of C 2 N + 2 ions with C 2 H 2 and C 2 H 4 , only charge transfer occurs. For these reactions of C 2 N + 2 ions, the most exothermic channel is dominant in each instance and occurs at or near the collision rate. Rate coefficients are also reported for association (condensation) of C 2 N + 2 ions with CO, CO 2 , C 2 H 2 and C 2 H 4 .

Reactions of CH3OCH2+ with hydrocarbons and O, N, and S compounds: applications for chemical ionization in selected ion flow tube studies

We report the results of a flowing afterglow ion source-selected ion flow tube study (FA-SIFT) of the reactions of the methoxymethyl cation, CH3OCH2+. Rate coefficients and product branching ratios are reported for twenty nine reagent molecules including those that constitute the major ingredients of air, the hydrocarbons CH4, C2H6, C3H8, n-C4H10, C2H2, C2H4, C3H4 (allene and propyne), C6H6, and the S-containing molecules H2S, CH3SH, C2H5SH, (CH3)2SH, and (C2H5)2SH. In addition, we examined the reactions with the N-containing molecules NH3, CH3NH2, (CH3)2NH, (CH3)3N, pyrrole, pyridine as well as CH3COCH3. The results can be summarized under three general reaction types: Reaction at the CH3 carbon, reaction at the CH2 carbon, and association. The results also indicate that the methoxymethyl cation can be used as a chemical ionization source for the detection of trace levels of S-containing compounds in saturated hydrocarbons.

EXPERIMENTAL AND THEORETICAL STUDY OF THE ENERGETICS OF TRIALKYLSULFONIUM IONS

Abstract The clustering reaction of dimethyl sulfide with t-butyl cation was examined using high pressure mass spectrometry. A lower limit of 581±10xa0kJ/mol for the standard enthalpy of formation of trimethylsulfonium ion at 298xa0K was obtained from the energetics of the clustering reaction and derived enthalpies of formation for t-butyl cation (711±5xa0kJ/mol), t-butyl-dimethylsulfonium ion (492±6xa0kJ/mol) and 2,3,3-trimethyl-2-butylcation (t-butyldimethylcarbenium ion, 622±7xa0kJ/mol). A second estimate of 595±11xa0kJ/mol was extrapolated from trends in the methyl cation affinities of analogous oxygen, nitrogen and sulfur compounds. G2(MP2) calculations combined with isogyric reactions lead to a predicted standard enthalpy of formation of 593±10xa0kJ/mol for trimethylsulfonium ion and a methyl cation affinity of 463±11xa0kJ/mol for dimethylsulfide. The computational results lie at the lower end of the range of 615±15xa0kJ/mol reported for this enthalpy of formation based on an appearance potential measurement of dimethylsulfide radical cation from trimethylsulfonium ion.

Proton affinity of cyanogen and association reactions of C2N2H+ and C2N2CH3+

Abstract The proton affinity (PA) of cyanogen (C 2 N 2 ) was redetermined through selected ion flow tube (SIFT) measurement of the rate coefficients of the reaction C 2 H 3 + + C 2 N 2 = C 2 N 2 H + + C 2 H 2 in both directions. The observed ΔG o 300 = −6.1 kJ mol −1 and derived ΔH o = −10.6 kJ mol −1 , and previous equilibrium results with CH 3 Cl, give PA(C 2 N 2 ) = 651.2 ± 2 kJ mol −1 . The results are consistent with the recently revised PA(CH 3 Cl) = 647.3 kJ mol −1 , and in good agreement with recent high-level theoretical values of PA(C 2 N 2 ) = 655–657 kJ mol −1 . We also observed that SO 2 H + transfers a proton to C 2 N 2 as well as to C 2 H 2 , and that in the reverse direction, the new reaction C 2 H 3 + + SO 2 → CH 2 SOH + + CO occurs but no proton transfer, indicating that PA(SO 2 ) −1 . The methylated species C 2 N 2 CH 3 + does not transfer a methyl cation to HCN, CH 3 CN, (CH 3 ) 2 CO and (CH 3 ) 3 N. However, association is observed in these systems and in the reactions of C 2 N 2 H + with C 2 H 2 and SO 2 . These processes can contribute to the astrochemical synthesis of complex heteroatom containing organics. In particular, we observe the apparently covalent C 2 N 2 H + · C 2 H 2 adduct, an isomer of deprotonated 1,4-diazine, which suggests that similar reactions of other C 2 N 2 containing ions and acetylenes can yield pyrimidine nucleic bases by simple ion-molecule processes.