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Chemical Shift and Coupling Constant Analysis of Dibenzyloxy Disulfides

Abstract (Expand)

Dialkoxy disulfides have found applications in the realm of organic synthesis as an S2 or alkoxy donor, under thermal and photolytic decompositions conditions, respectively. Spectrally, dibenzyloxy … disulfides possess an ABq in the 1H NMR, which can shift by over 1.1 ppm depending on the substituents present on the aromatic ring, as well as the solvent employed. The effect of the said substituents and solvent were analyzed and compared to the center of the ABq, geminal coupling, and the differences in chemical shifts of the individual doublets. Additionally, quantum-chemical calculations demonstrated the intramolecular H-bonding arrangement, found within the dibenzyloxy disulfides.

Authors: Eric G. Stoutenburg, Ganna Gryn’ova, Michelle L. Coote, Ronny Priefer

Date Published: 1st Feb 2015

Publication Type: Journal

Experimental Evidence for Competitive N-O and O-C Bond Homolysis in Gas-Phase Alkoxyamines

Abstract (Expand)

The extensive use of alkoxyamines in controlled radical polymerisation and polymer stabilisation is based on rapid cycling between the alkoxyamine (R1R2NOR3) and a stable nitroxyl radical (R1R2NO•) via … homolysis of the labile OC bond. Competing homolysis of the alkoxyamine NO bond has been predicted to occur for some substituents leading to production of aminyl and alkoxyl radicals. This intrinsic competition between the OC and NO bond homolysis processes has to this point been difficult to probe experimentally. Herein we examine the effect of local molecular structure on the competition between NO and OC bond cleavage in the gas phase by variable energy tandem mass spectrometry in a triple quadrupole mass spectrometer. A suite of cyclic alkoxyamines with remote carboxylic acid moieties (HOOCR1R2NOR3) were synthesised and subjected to negative ion electrospray ionisation to yield [M − H]− anions where the charge is remote from the alkoxyamine moiety. Collision-induced dissociation of these anions yield product ions resulting, almost exclusively, from homolysis of OC and/or NO bonds. The relative efficacy of NO and OC bond homolysis was examined for alkoxyamines incorporating different R3 substituents by varying the potential difference applied to the collision cell, and comparing dissociation thresholds of each product ion channel. For most R3 substituents, product ions from homolysis of the OC bond are observed and product ions resulting from cleavage of the NO bond are minor or absent. A limited number of examples were encountered however, where NO homolysis is a competitive dissociation pathway because the OC bond is stabilised by adjacent heteroatom(s) (e.g. R3 = CH2F). The dissociation threshold energies were compared for different alkoxyamine substituents (R3) and the relative ordering of these experimentally determined energies is shown to correlate with the bond dissociation free energies, calculated by ab initio methods. Understanding the structure-dependent relationship between these rival processes will assist in the design and selection of alkoxyamine motifs that selectively promote the desirable OC homolysis pathway.

Authors: David L. Marshall, Ganna Gryn'ova, Michelle L. Coote, Philip J. Barker, Stephen J. Blanksby

Date Published: 1st Feb 2015

Publication Type: Journal

Dynamics of CYP51: implications for function and inhibitor design

Abstract

Not specified

Authors: Xiaofeng Yu, Vlad Cojocaru, Ghulam Mustafa, Outi M. H. Salo-Ahen, Galina I. Lepesheva, Rebecca C. Wade

Date Published: 1st Feb 2015

Publication Type: Journal

Ten Simple Rules for Organizing an Unconference

Abstract

Not specified

Authors: Aidan Budd, Holger Dinkel, Manuel Corpas, Jonathan C. Fuller, Laura Rubinat, Damien P. Devos, Pierre H. Khoueiry, Konrad U. Förstner, Fotis Georgatos, Francis Rowland, Malvika Sharan, Janos X. Binder, Tom Grace, Karyn Traphagen, Adam Gristwood, Natasha T. Wood

Date Published: 29th Jan 2015

Publication Type: Journal

SN2014J gamma rays from the 56Ni decay chain

Abstract

Not specified

Authors: Roland Diehl, Thomas Siegert, Wolfgang Hillebrandt, Martin Krause, Jochen Greiner, Keiichi Maeda, Friedrich K. Röpke, Stuart A. Sim, Wei Wang, Xiaoling Zhang

Date Published: 28th Jan 2015

Publication Type: Journal

OGLE-2013-SN-079: A Lonely Supernova Consistent with a Helium Shell Detonation

Abstract

Not specified

Authors: C. Inserra, S. A. Sim, L. Wyrzykowski, S. J. Smartt, M. Fraser, M. Nicholl, K. J. Shen, A. Jerkstrand, A. Gal-Yam, D. A. Howell, K. Maguire, P. Mazzali, S. Valenti, S. Taubenberger, S. Benitez-Herrera, D. Bersier, N. Blagorodnova, H. Campbell, T.-W. Chen, N. Elias-Rosa, W. Hillebrandt, Z. Kostrzewa-Rutkowska, S. Kozłowski, M. Kromer, J. D. Lyman, J. Polshaw, F. K. Röpke, A. J. Ruiter, K. Smith, S. Spiro, M. Sullivan, O. Yaron, D. Young, F. Yuan

Date Published: 20th Jan 2015

Publication Type: Journal

Testing the Role of SNe Ia for Galactic Chemical Evolution of p-nuclei with Two-dimensional Models and with s-process Seeds at Different Metallicities

Abstract

Not specified

Authors: C. Travaglio, R. Gallino, T. Rauscher, F. K. Röpke, W. Hillebrandt

Date Published: 20th Jan 2015

Publication Type: Journal

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