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Reaction of Distonic Aryl and Alkyl Radical Cations with Amines: The Role of Charge and Spin Revealed by Mass Spectrometry, Kinetic Studies, and DFT Calculations
Author(s) -
Andrikopoulos Benjamin,
Sidhu Parvinder K.,
Taggert Bethany I.,
Nathanael Joses G.,
O'Hair Richard A. J.,
Wille Uta
Publication year - 2020
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201900706
Subject(s) - chemistry , radical ion , photochemistry , homolysis , aryl , radical , radical disproportionation , pyridinium , aryl radical , nucleophile , amine gas treating , fragmentation (computing) , alkyl , medicinal chemistry , hydrogen atom abstraction , organic chemistry , ion , disproportionation , catalysis , computer science , operating system
Gas‐phase reaction of the aromatic distonic radical cations 4‐Pyr +. and 3‐Pyr +. with amines led to formation of the corresponding amino pyridinium ions 4‐Pyr + NR 2 and 3‐Pyr + NR 2 through amine addition at the site of the radical, followed by homolytic β‐fragmentation. The reaction efficiencies range from 66–100 % for 4‐Pyr +. and 57–86 % for 3‐Pyr +. , respectively, indicating practically collision‐controlled processes in some cases. Computational studies revealed that the combination of positive charge and spin makes nucleophilic attack by the amine at the site of the radical barrierless and strongly exothermic by about 175±15 kJ mol −1 , thereby rendering ‘conventional’ radical pathways through hydrogen abstraction or addition onto π systems less important. Exemplary studies with 4‐Pyr +. showed that this reaction can be reproduced in solution. A similar addition/radical fragmentation sequence occurs also in the gas‐phase reaction of amines with the aliphatic distonic radical cation Oxo + C . , showing that the observed charge‐spin synergism is not limited to aromatic systems.