Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Epoxides in Biological Processes
Document related concepts
no text concepts found
Transcript
Section 17.13 EPOXIDES IN BIOLOGICAL PROCESSES Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Monooxygenases • Some monooxygenase enzymes catalyze epoxidation of biological alkenes by O2 • A reducing agent (NADH) is required along with an “oxidizing” proton • Epoxidation of squalene is an important example Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Section 17.14 PREPARATION OF SULFIDES Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Preparation of Sulfides via SN2 • Thiolate anions are great nucleophiles • Sulfides can be prepared via SN2 of thiolates with alkyl halides The usual trends and limitations of SN2 still apply to these reactions. Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Section 17.15 OXIDATION OF SULFIDES: SULFOXIDES AND SULFONES Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Oxidation of Sulfides • Unlike ethers, sulfurs are typically oxidized at sulfur (the strength of the S–O bond is an important factor) • One or two oxidation events may occur 1 eq. H2O2 2 eq. H2O2 Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Section 17.16 ALKYLATION OF SULFIDES: SULFONIUM SALTS Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Alkylation of Sulfides • Neutral sulfides react with alkyl halides in SN2 reactions to form sulfonium salts • Sulfoniums are much more stable than analogous oxonium salts of ethers Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Nature’s Methylating Agent • Nature uses a methylsulfonium salt as an electrophilic methylating agent: S-adenosylmethionine (SAM) Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Section 17.17 SPECTROSCOPIC ANALYSIS OF ETHERS, EPOXIDES, AND SULFIDES Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Infrared Spectroscopy • Ethers have a characteristic band due to antisymmetric C–O–C stretch around 1100 cm–1 • Sulfides have weak bands around 600 cm–1 • The S–O bonds in sulfoxides and sulfones are stronger and give stronger bands at higher wavenumbers Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 1H NMR Spectroscopy • Ether H–C–OR protons have chemical shift similar to the corresponding proton in alcohols: d 3.2 – 4.0 • Just like thiols, the corresponding proton in sulfides H–C–SR is further upfield (why?): d 2.0 – 3.0 • Epoxide protons are surprisingly shielded: d 2.5 Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 13C NMR Spectroscopy • Ether carbons C–O–C are somewhat deshielded: d 57 – 87 • As for protons, sulfide carbons C–S–C are more shielded Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Mass Spectrometry • Ethers and sulfides can both lose an alkyl radical to form an O- or S-stabilized carbocation • Often, this fragment is more abundant than the molecular ion Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Related documents