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11.
12.
The mass spectral properties under medium and high resolution of a new protecting group for sterols is described and its ability to direct fragmentation is compared with established derivatives. The mass spectra obtained are characterised by strong molecular ions which fragment to produce a more even ion distribution than the familiar TMS ethers. This results in enhanced abundance of hydrocarbon fragments, with molecular structural details given greater prominence than is found with other derivatives. 相似文献
13.
Norbert V. Fehringer Dalia M. Gilvydis Stephen M. Walters Colin F. Poole 《Journal of separation science》1992,15(2):124-127
The combination of open tubular column gas chromatography with electrolytic conductivity detection has been evaluated for the determination of nitrogen-containing pesticide residues in food extracts. Optimization of the column position at the column-detector interface was crucial to the successful operation of the detector. The signal-to-noise ratio and response stability of the detector are greatly influenced by the composition of the electrolyte solvent. Large volume splitless injections using retention gaps and optimized detector operating conditions enabled pesticide residues in food extracts to be determined at sub parts-per-million levels. Although the electrolytic conductivity detector is less sensitive than the thermionic ionization detector, its greater nitrogen selectivity can he crucial to the determination of nitrogen-containing contaminants in food extracts, particularly in complex mixtures where phosphorus-containing contaminants or matrix compounds are also present. 相似文献
14.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
15.
Andrew J. Smith Daniela Dimitrova Jude N. Arokianathar Kenneth F. Clark Darren L. Poole Stuart G. Leach John A. Murphy 《Chemical science》2020,11(45):12364
The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them.The combination of potassium tert-butoxide and triethylsilane provides simultaneous access to multiple reactive intermediates, radicals, H-atom donors, hydride donors and electron donors, giving scope for unprecedented reaction outcomes. 相似文献
16.
17.
B. R. Sheridan G. Poole E. Dowdall C. Chiu 《International journal of environmental analytical chemistry》2013,93(2-4):195-202
Abstract The analysis of PCBs often involves lengthy and expensive cleanup procedures to remove interferences associated with environmental sample matrices. Gel permeation chromatography (GPC) has proven to be a useful tool in removing many of these interferences from environmental samples, especially from difficult matrices such as oils, lipids and sediments. This paper describes the effect of temperature upon the GPC column in separating PCBs from transformer oil and its implication on GC-MS analysis. 相似文献
18.
Rhodium‐Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of α‐Branched Products 下载免费PDF全文
Dr. Louis K. M. Chan Darren L. Poole Di Shen Dr. Mark P. Healy Prof. Timothy J. Donohoe 《Angewandte Chemie (International ed. in English)》2014,53(3):761-765
The rhodium‐catalyzed methylation of ketones has been accomplished using methanol as the methylating agent and the hydrogen‐borrowing method. The sequence is notable for the relatively low temperatures that are required and for the ability of the reaction system to form α‐branched products with ease. Doubly alkylated ketones can be prepared from methyl ketones and two different alcohols by using a sequential one‐pot iridium‐ and rhodium‐catalyzed process. 相似文献
19.
Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron‐Rich Substrates
Sayad Doobary Alexi T. Sedikides Henry P. Caldora Darren L. Poole Alastair J. J. Lennox 《Angewandte Chemie (International ed. in English)》2020,59(3):1155-1160
Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their preparation, yet current methods are limited in their alkene‐types and tolerance of electron‐rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a number of unactivated alkene‐types that is tolerant of electron‐rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator using an “ex‐cell” approach, which avoids oxidative substrate decomposition. The more sustainable conditions give good to excellent yields in up to decagram scales. 相似文献
20.
Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron-Rich Substrates
Sayad Doobary Alexi T. Sedikides Henry P. Caldora Dr. Darren L. Poole Dr. Alastair J. J. Lennox 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1171-1176
Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their preparation, yet current methods are limited in their alkene-types and tolerance of electron-rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a number of unactivated alkene-types that is tolerant of electron-rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator using an “ex-cell” approach, which avoids oxidative substrate decomposition. The more sustainable conditions give good to excellent yields in up to decagram scales. 相似文献