Submerged Barriers in the Ni super(+) Assisted Decomposition of Propionaldehyde

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 120; no. 15; pp. 2275 - 2284
• Main Author: Mansell, A
• Format: Journal Article
• Language: English
• Published: 21.04.2016
• Subjects: Barriers; Carbon; Carbon-carbon composites; Energy measurement; Insertion; Mathematical analysis; Photons; Submerged
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.5b08444

The reaction dynamics of the Ni super(+) mediated decarbonylation of propionaldehyde was assessed using the single photon initiated decomposition rearrangement reaction (SPIDRR) technique. The exothermic production of Ni super(+)CO was temporally monitored and the associated rate constants, k(E), were extracted as a function of activating photon energy. In addition, the reaction potential energy surface was calculated at the UCCSD(T)/def2-TZVP//PBEPBE/cc-pVDZ level of theory to provide an atomistic description of the reaction profile. The decarbonylation of propionaldehyde can be understood as proceeding through parallel competitive reaction pathways that are initiated by Ni super(+) insertion into either the C-C or C-H bond of the propionaldehyde carbonyl carbon. Both paths lead to the elimination of neutral ethane and are governed by submerged barriers. The lower energy sequence is a consecutive C-C/C-H addition process with a submerged barrier of 14 350 plus or minus 600 cm super(-1). The higher energy sequence is a consecutive C-H/C-C addition process with a submerged barrier of 15 400 plus or minus 600 cm super(-1). Both barriers were determined using RRKM calculations fit to the experimentally determined k(E) values. The measured energy difference between the two barriers agrees with the DFT computed difference in rate limiting transition-state energies, 18 413 and 19 495 cm super(-1).