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Methide transfer reactions play important roles in many areas of chemistry, including the Grignard reaction, in the transmetalation steps of metal-catalyzed cross-coupling reactions, and in the generation of cationic metal polymerization catalysts. Methide affinities (MAs) are the key thermodynamic quantity that underpin such reactions, and yet comprehensive methide affinity scales are poorly developed. Here, B3LYP-D3BJ/def2-TZVP calculations are used to calculate the energy changes (MAs) for cations (MeZ → Z + + Me - ), neutrals (MeY - → Y + Me - ), and anions (MeX 2- → X - + Me - ) derived from permethyl species of all group s and p elements. The MAs range from 2525.8 for the singlet cation F + to -820.4 kJ/mol for the tetramethylborate anion, Me 4 B - . The cations show the clearest trends: the MAs in all cases decrease going down the group, while moving across a period, the MAs increase from group 1 to group 2 and then decrease for group 3, remaining about the same or with a modest increase moving to group 4, and then continue to increase across a period to a maximum for the halogens (group 17). The anions and dianions are sensitive to hypervalency; those elements that cannot expand the octet have very unfavorable MAs (e.g., MA of Me 4 C requires the formation of Me 5 C - and of Me 4 B - requires the formation of Me 5 B 2- ). To address whether the anion MeY - and dianion MeZ 2- are stable, the vertical detachment energies of the anions and dianions were calculated. All of the anions are thermodynamically stable with respect to electron loss, except for Me 4 N - , while the dianions are all thermodynamically unstable with respect to electron loss. The kinetic stability of the dianions with respect to methide and electron loss was also evaluated for the lowest MAs. The only dianions that might be kinetically stable and observable in the gas phase are Me 4 Ca 2- , Me 4 Sr 2- , and Me 4 Ba 2- . The dianion CF 3 CaF 3 2- is predicted to be both thermodynamically and kinetically stable in the gas phase.

The gas-phase ion-molecule identity exchange reactions of phenyl chalcogen iranium ions with alkenes have been examined experimentally in a linear ion trap mass spectrometer by isotope labeling experiments. The nature of both the alkene and the chalcogen play crucial roles, with the bimolecular rates for π-ligand exchange following the order: [PhTe( c -C 6 H 10 )] + + c -C 6 D 10 > [PhTe(C 2 D 4 )] + + C 2 H 4 > [PhSe( c -C 6 H 10 )] + + c -C 6 D 10 , with no reaction being observed for [PhSe(C 2 D 4 )] + + C 2 H 4 , [PhS(C 2 D 4 )] + + C 2 H 4 , and [PhS( c -C 6 H 10 )] + + c -C 6 D 10 . The experimental results correlate with RRKM modeling and density functional theory (DFT) calculations, which also demonstrates that these reactions proceed via associative mechanisms. Natural bond orbital (NBO) analysis reveals a shift in the association complexes from a σ-hole interaction to ones mirroring the π-p + and n-π* at the transition state in accordance with the rates of reaction.

A novel precursor to the distonic O- and C-centered radical cations Oxo + O • and Oxo + C • was designed and synthesized, which represents model systems for radicals produced during polyester degradation. The precursor is equipped with a nitrate functional group, which serves as a masked site for these alkoxyl and carbon radicals that are unleashed through collision-induced dissociation (CID). Oxo + O • and Oxo + C • feature a cyclic carboxonium ion as permanent charge tag to enable monitoring their ion-molecule reactions on the millisecond to second time scale in the ion trap of the mass spectrometer. The reactions of Oxo + O • and Oxo + C • with cyclohexene, cyclohexadiene, ethyl acetate, 1,1-dimethoxyethane, and 1,2-dimethoxyethane, which exhibit structural features present in both intact and defective polyesters, were explored through product and kinetic studies to identify "hot spots" for radical-induced damage in polyesters. All reactions with Oxo + O • were extremely fast and proceeded predominantly through HAT. Oxo + C • was about two orders of magnitude less reactive and did not noticeably damage aliphatic ester moieties through hydrogen abstraction on the time scale of our experiments. Radical addition to alkene π systems was identified as an important pathway for C-radicals, which needs to be included in polymer degradation mechanisms.

Experimental and computational quantum chemistry investigations of the gas-phase ion-molecule reactions between the distonic ions + H 3 N(CH 2 ) n S • (n = 2-4) and the reagents dimethyl disulfide, allyl bromide, and allyl iodide demonstrate that intramolecular hydrogen bonding can modulate the reactivity of thiyl radicals. Thus, the 3-ammonium-1-propanethiyl radical (n = 3) exhibits the lowest reactivity of these distonic ions toward all substrates. Theoretical calculations on this distonic ion highlight that its most stable conformation involves a six-membered ring configuration, and that it has the strongest intramolecular hydrogen bond. In addition, the calculations indicate that the barrier heights for radical abstraction by this hydrogen-bond-stabilized 3-ammonium-1-propanethiyl radical are the highest among the systems examined, consistent with the experimental observations.