Comparison of the Reactivity of the Three Distonic Isomers of the Pyridine Radical Cation Toward Tetrahydrofuran in Solution and in the Gas Phase

Widjaja, Fanny; Jin, Zhicheng; Nash, John J.; Kenttämaa, Hilkka I.

doi:10.1007/s13361-012-0543-3

Cited by 11 publications

(12 citation statements)

References 24 publications

(51 reference statements)

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“…[43][44] As radical electrophilicity increases, the effect becomes more pronounced with increasing proximity between radical and charge site. This effect has previously been observed and described in greater detail in the gas 45 and liquid phase [46][47] energetically favourable and might be expected to result in more m/z 93 signal than is observed experimentally (Figure 3). Therefore, quantum state counting was performed on several competing transition states to quantify entropic factors contributing to the observed product branching ratios.…”

Section: Synthesis Of Dehydro-n-pyridinium Radical Cationssupporting

confidence: 73%

Highly efficient gas-phase reactivity of protonated pyridine radicals with propene

Bright

Prendergast

Kelly

et al. 2017

Phys. Chem. Chem. Phys.

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Small nitrogen containing heteroaromatics are fundamental building blocks for many biological molecules, including the DNA nucleotides. Pyridine, as a prototypical N-heteroaromatic, has been implicated in the chemical evolution of many extraterrestrial environments, including the atmosphere of Titan. This paper reports on the gas-phase ion-molecule reactions of the three dehydro-N-pyridinium radical cation isomers with propene. Photodissociation ion-trap mass spectrometry experiments are used to measure product branching ratios and reaction kinetics. Reaction efficiencies for 2-dehydro-N-pyridinium, 3-dehydro-N-pyridinium and 4-dehydro-N-pyridinium with propene are 70%, 47% and 41%, respectively. The m/z 106 channel is the major product channel across all cases and assigned 2-, 3-, and 4-vinylpyridinium for each reaction. The m/z 93 channel is also significant and assigned the 2-, 3-, and 4-N-protonated-picolyl radical cation for each case. H-Abstraction from propene is not competitive under experimental conditions. Potential energy schemes, at the M06-2X/6-31(2df,p) level of theory and basis set, are described to assist in rationalising observed product branching ratios and elucidating possible reaction mechanisms. Reaction barriers to the production of vinylpyridinium (m/z 106) + CH are the lowest identified for the 3- and 4-dehydro-N-pyridinium reactions, in support of the observed dominance of the m/z 106 ion signal. Ethylene loss via ring-mediated H-transfer along the propyl group is found to be the lowest energy pathway for the 2-dehydro-N-pyridinium reaction, suggesting a preference toward m/z 93 (N-protonated-picolyl radical cation) over the experimentally observed products. Entropic bottle-necks along the m/z 93 pathway however, associated with ring-mediated H-atom transfer, are responsible for the dominance of m/z 106 in the 2-dehydro-N-pyridinium + propene reaction. For all three isomers, computed barriers for all observed reaction channels were below the entrance channel, suggesting these reactions can contribute to molecular weight growth in extraterrestrial environments with accelerated reaction rates in low temperature regions of space.

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Section: Synthesis Of Dehydro-n-pyridinium Radical Cationssupporting

confidence: 73%

Highly efficient gas-phase reactivity of protonated pyridine radicals with propene

Bright

Prendergast

Kelly

et al. 2017

Phys. Chem. Chem. Phys.

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“…Since Kenttämaa et al . showed in previous work that distonic pyridine radical cations react with ethers, such as THF, in the condensed phase through both radical and non‐radical pathways, we explored whether the results from our mass spectrometric studies could also be reproduced in solution…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2020

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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 À 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.

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“…As a control, we also investigated E1 with a tert ‐butyl group in the α ‐position (Figure ). The present investigation also sheds light on distonic radical cations in solution because these highly reactive species are only rarely described …”

Section: Introductionmentioning

confidence: 81%

Detection and follow‐up reactions of distonic β,β‐dimesityl enol radical cations containing nitrogen heterocyclic bases

Çınar

Lal

Deiseroth

et al. 2018

J of Physical Organic Chem

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β,β-Dimesityl enols E2-E4 containing various nitrogen heterocyclic bases in the α-position were investigated by laser flash photolytic oxidation and density functional theory in order to identify distonic enol radical cations in solution and characterize their immediate follow-up reactions. Enol E1 with a tert-butyl group in the α-position served as a reference. Experimental and computational efforts reveal that one-electron oxidation of enol E1 furnishes the enol radical cation, whereas oxidation of E2-E4 provides distonic radical cations in solution. While the distonic radical cations of E2-E3 undergo intermolecular acid-base reactions, the distonic radical cation of E4 experiences an intramolecular hydrogen abstraction followed by subsequent ring closure and ring-opening steps. As a final product on the laser flash photolysis time scale, the rearranged radical cation E4d-R is generated that is characterized by a dimesitylmethyl radical subunit. KEYWORDS cyclic voltammetry (CV), density functional theory (DFT), distonic radical cation, laser flash photolysis (LFP), enol radical cation

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Comparison of the Reactivity of the Three Distonic Isomers of the Pyridine Radical Cation Toward Tetrahydrofuran in Solution and in the Gas Phase

Cited by 11 publications

References 24 publications

Highly efficient gas-phase reactivity of protonated pyridine radicals with propene

Highly efficient gas-phase reactivity of protonated pyridine radicals with propene

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

Detection and follow‐up reactions of distonic β,β‐dimesityl enol radical cations containing nitrogen heterocyclic bases

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