Gas-Phase Reactions of the Iodide Ion with Chloromethane and Bromomethane:  Competition between Nucleophilic Displacement and Halogen Abstraction

Abstract

Guided ion beam tandem mass spectrometry techniques are used to measure the reaction cross sections of the collisionally activated process I -+ CH 3 Y f products, where Y ) Cl and Br. The Cland Brproducts are observed at the lowest collision energies. A back-side attack S N 2 reaction is responsible for the initial rise from the threshold. At higher collision energies, the ICland IBrions are observed and signify competition from a front-side-attack, halogen-abstraction reaction. All the reactions are endoergic and exhibit excess threshold energies, E 0 , when compared with established reaction endothermicities from the literature, ∆H 0 . The reaction mechanisms are explored with the aid of CCSD(T)/LanL2DZ and CCSD(T)/SDD molecular orbital calculations and phase space theory.

Energy landscapes of nucleophilic substitution reactions: A comparison of density functional theory and coupled cluster methods

“…Tables S1–S3 in the supporting information contain the CCSD(T) benchmark data for the energy profiles of the reactions in the three sets of reference data (A, B, and C, see Table 1) taken from the literature 13, 15, 55–75. Each of the original articles are referred to by the letter of the reference set plus a number, e.g., A1 for Ref 55.…”

Evaluating the Thermal Vinylcyclopropane Rearrangement (VCPR) as a Practical Method for the Synthesis of Difluorinated Cyclopentenes: Experimental and Computational Studies of Rearrangement Stereospecificity

“…Methyl halides (CH 3 X, X=F, Cl, Br, I) are frequently employed as model compounds in gas‐phase reactions1 to study at a molecular level mechanistic aspects of CH and CX bond activation. These ion/molecule reactions can be classified in four different types: 1) nucleophilic substitution when CH 3 X is reacted with anions resulting in the formation X − ;1b,d,e,i,n,p,q,r,x,z 2) halide atom abstraction by metal cations1t–v or anions;1p 3) proton, hydride or hydrogen‐atom abstraction by anions1b,k,x or cations,1v respectively; 4) dehydrogenation or dehydrohalogenation promoted by metal cations 1v. In all these processes, only one or two bonds of the methyl halide are activated.…”

Acetic Acid from the Carbonylation of Chloride Methane Over Rhodium Based Catalysts

“…This is a multistep process that includes oxidative addition, ligand migration, carbon monoxide insertion, and reductive elimination [21]. Similarly, chloride methane and KI in the current reaction system may be converted to methyl iodide by Cl-I exchange [22], and the methyl iodide generated then may participate in the multistep carbonylation cycle and give acetic acid as the final product. It is believed that the rate determining steps were different in the rhodium and iridium catalytic processes.…”