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Special Issue "Radical Chemistry"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Synthesis".

Deadline for manuscript submissions: closed (10 February 2018)

Special Issue Editor

Guest Editor
Prof. Dr. John C. Walton

EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, U.K.
Website | E-Mail
Interests: radical chemistry; organic synthetic methods; free-radical rearrangements; photoredox catalysis; oxime derivatives; EPR spectroscopy; DFT applications; enhanced acidity of radicals

Special Issue Information

Dear Colleagues,

 

Radicals play an astonishing variety of roles in an amazingly diverse range of sciences and technologies. Our understanding of the almost unlimited flexibility of their structures and the huge breadth of their activities has expanded wonderfully in the last few years. Notable new advances include: The burgeoning exploitation of photoredox catalysis in mild synthetic procedures, boron-containing radicals in syntheses, oxime derivatives as radical precursors, radical cascade reactions, novel controlled/living radical mediated polymerization methods, double spin labelling for EPR distance measurements in biopolymers and organic super electron donors. Radical-mediated syntheses are steadily taking their place alongside more traditional nucleophile/electrophile preparative procedures. In fact, radical-mediated preparations frequently enable tedious protection/deprotection steps to be dispensed with and this, coupled with the neutral conditions and absence of harsh acidic/basic reagents, makes their use particularly attractive. Radical reactivity depends strongly on the underlying thermodynamics. Key thermodynamic parameters have been obtained for many model radicals and archetype radical clocks are available for assessing reactivity. These tools, supplemented and augmented by DFT computational methods, ensure that synthetic planning is comparatively easy and that mechanisms can be rationally established. Furthermore, radical intermediates can often be elegantly characterized and monitored by EPR spectroscopic methods. Persistent radicals are finding more and more uses in both biological and materials sciences. The aim of this Special Issue is to review and showcase recent research across the whole field. Papers and review articles are welcomed in the heartland areas of radical-based synthesis and physical organic chemistry, as well as in all the newly-developing fields.

Prof. Dr. John C. Walton
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Reactive intermediates
  • Radical-mediated synthetic methods
  • Radical reagents
  • Radical cyclizations
  • Radical rearrangements
  • Radical kinetics and mechanisms
  • Redox properties of radicals
  • Thermochemistry of radicals
  • Photoredox catalysis
  • Nitroxides
  • Spin trapping and spin labelling
  • Autoxidations
  • Radical mediated polymerizations
  • Applications of EPR spectroscopy

Published Papers (5 papers)

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Research

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Open AccessFeature PaperArticle Microhydration and the Enhanced Acidity of Free Radicals
Molecules 2018, 23(2), 423; doi:10.3390/molecules23020423
Received: 31 January 2018 / Revised: 9 February 2018 / Accepted: 14 February 2018 / Published: 14 February 2018
PDF Full-text (1151 KB)
Abstract
Recent theoretical research employing a continuum solvent model predicted that radical centers would enhance the acidity (RED-shift) of certain proton-donor molecules. Microhydration studies employing a DFT method are reported here with the aim of establishing the effect of the solvent micro-structure on the
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Recent theoretical research employing a continuum solvent model predicted that radical centers would enhance the acidity (RED-shift) of certain proton-donor molecules. Microhydration studies employing a DFT method are reported here with the aim of establishing the effect of the solvent micro-structure on the acidity of radicals with and without RED-shifts. Microhydration cluster structures were obtained for carboxyl, carboxy-ethynyl, carboxy-methyl, and hydroperoxyl radicals. The numbers of water molecules needed to induce spontaneous ionization were determined. The hydration clusters formed primarily round the CO2 units of the carboxylate-containing radicals. Only 4 or 5 water molecules were needed to induce ionization of carboxyl and carboxy-ethynyl radicals, thus corroborating their large RED-shifts. Full article
(This article belongs to the Special Issue Radical Chemistry)
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Open AccessArticle Novel Carbazole Skeleton-Based Photoinitiators for LED Polymerization and LED Projector 3D Printing
Molecules 2017, 22(12), 2143; doi:10.3390/molecules22122143
Received: 31 October 2017 / Revised: 27 November 2017 / Accepted: 30 November 2017 / Published: 4 December 2017
PDF Full-text (4354 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Radical chemistry is a very convenient way to produce polymer materials. Here, an application of a particular photoinduced radical chemistry is illustrated. Seven new carbazole derivatives Cd1Cd7 are incorporated and proposed as high performance near-UV photoinitiators for both the free radical
[...] Read more.
Radical chemistry is a very convenient way to produce polymer materials. Here, an application of a particular photoinduced radical chemistry is illustrated. Seven new carbazole derivatives Cd1Cd7 are incorporated and proposed as high performance near-UV photoinitiators for both the free radical polymerization (FRP) of (meth)acrylates and the cationic polymerization (CP) of epoxides utilizing Light Emitting Diodes LEDs @405 nm. Excellent polymerization-initiating abilities are found and high final reactive function conversions are obtained. Interestingly, these new derivatives display much better near-UV polymerization-initiating abilities compared to a reference UV absorbing carbazole (CARET 9H-carbazole-9-ethanol) demonstrating that the new substituents have good ability to red shift the absorption of the proposed photoinitiators. All the more strikingly, in combination with iodonium salt, Cd1Cd7 are likewise preferred as cationic photoinitiators over the notable photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) for mild irradiation conditions featuring their remarkable reactivity. In particular their utilization in the preparation of new cationic resins for LED projector 3D printing is envisioned. A full picture of the included photochemical mechanisms is given. Full article
(This article belongs to the Special Issue Radical Chemistry)
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Open AccessArticle Theoretical Study of ClOO + NO Reaction: Mechanism and Kinetics
Molecules 2017, 22(12), 2121; doi:10.3390/molecules22122121
Received: 30 October 2017 / Revised: 16 November 2017 / Accepted: 20 November 2017 / Published: 1 December 2017
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Abstract
Theoretical investigations are performed on mechanism and kinetics of the reaction of halogen peroxy radical ClOO with NO radical. The electronic structure information for both of the singlet and triplet potential energy surfaces (PESs) is obtained at the MP2/6-311 + G(2df) level of
[...] Read more.
Theoretical investigations are performed on mechanism and kinetics of the reaction of halogen peroxy radical ClOO with NO radical. The electronic structure information for both of the singlet and triplet potential energy surfaces (PESs) is obtained at the MP2/6-311 + G(2df) level of theory, and the single-point energies are refined by the CCSD(T)/6-311 + G(2df) level. The rate constants for various product channels of the reaction in the pressure range of 1-7600 Torr are predicted. The main results are as follows: On the singlet surface, the addition-elimination mechanism is the most important. First, the N atom of the NO radical can attack the O atom of the ClOO radical to form an energy-riched intermediate IM1 ClOONOtp (21.3 kcal/mol) barrierlessly, then IM1 could isomerizes to IM2 ClOONOcp (22.1 kcal/mol) via a low energy barrier. Both IM1 and IM2 can dissociate to the primary product P1 ClNO + 1O2 and the secondary product P2 ClO + NO2. On the triplet surface, the direct Cl-abstraction reaction is the most feasible pathway. The Cl-abstraction can take place via a van der Waals complex, 3IM1 ONClOO (4.1 kcal/mol), then it fragments readily to give P1’ ClNO + 3O2 with a small barrier. The kinetic calculations show that at low temperatures, the singlet bimolecular product P1 is the primary product, while at high temperatures, the triplet product P1’ becomes the primary one; only at high pressures and low temperatures, the unimolecular products IM1 and IM2 can be found with quite small yields. At experimentally measured temperature 213 K, ClNO is the primary product in the whole pressure range, which is consistent with the previous experiment. The present study may be useful for further experimental studies for the title reaction. Full article
(This article belongs to the Special Issue Radical Chemistry)
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Review

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Open AccessFeature PaperReview Radical Polymerization of Alkyl 2-Cyanoacrylates
Molecules 2018, 23(2), 465; doi:10.3390/molecules23020465
Received: 3 February 2018 / Revised: 15 February 2018 / Accepted: 17 February 2018 / Published: 20 February 2018
PDF Full-text (1224 KB)
Abstract
Cyanoacrylates (CAs) are well-known fast-setting adhesives, which are sold as liquids in the presence of stabilizers. Rapid anionic polymerization on exposure to surface moisture is responsible for instant adhesion. The more difficult, but synthetically more useful radical polymerization is only possible under acidic
[...] Read more.
Cyanoacrylates (CAs) are well-known fast-setting adhesives, which are sold as liquids in the presence of stabilizers. Rapid anionic polymerization on exposure to surface moisture is responsible for instant adhesion. The more difficult, but synthetically more useful radical polymerization is only possible under acidic conditions. Recommendations on the handling of CAs and the resulting polymers are provided herein. In this review article, after a general description of monomer and polymer properties, radical homo- and copolymerization studies are described, along with an overview of nanoparticle preparations. A summary of our recently reported radical polymerization of CAs, using reversible addition-fragmentation chain transfer (RAFT) polymerization, is provided. Full article
(This article belongs to the Special Issue Radical Chemistry)
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Open AccessReview Ultrafast Chemistry of Water Radical Cation, H2O•+, in Aqueous Solutions
Molecules 2018, 23(2), 244; doi:10.3390/molecules23020244
Received: 2 January 2018 / Revised: 19 January 2018 / Accepted: 22 January 2018 / Published: 26 January 2018
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Abstract
Oxidation reactions by radicals constitute a very important class of chemical reactions in solution. Radiation Chemistry methods allow producing, in a controlled way, very reactive oxidizing radicals, such as OH, CO3•–, NO3, SO4•–
[...] Read more.
Oxidation reactions by radicals constitute a very important class of chemical reactions in solution. Radiation Chemistry methods allow producing, in a controlled way, very reactive oxidizing radicals, such as OH, CO3•–, NO3, SO4•–, and N3. Although the radical cation of water, H2O•+, with a very short lifetime (shorter than 1 ps) is the precursor of these radicals in aqueous solutions, its chemistry is usually known to be limited to the reaction of proton transfer by forming OH radical. Herein, we stress situations where H2O•+ undergoes electron transfer reaction in competition with proton transfer. Full article
(This article belongs to the Special Issue Radical Chemistry)
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