16.14 Epoxides in Biological Processes

Naturally Occurring Epoxides are common are involved in numerous biological processes

Biosynthesis of Epoxides C + O2 H+ + NADH enzyme C C + H2O + NAD+ O enzyme-catalyzed oxygen transfer from O2 to alkene enzymes are referred to as monooxygenases

Example: biological epoxidation of squalene O2, NADH monoxygenase O this reaction is an important step in the biosynthesis of cholesterol

16.15 Preparation of Sulfides

prepared by nucleophilic substitution (SN2) Preparation of RSR' prepared by nucleophilic substitution (SN2) – •• • • •• R S R' R S + R' X NaSCH3 CH3CHCH CH2 Cl CH3CHCH CH2 SCH3 methanol

16.16 Oxidation of Sulfides: Sulfoxides and Sulfones

Oxidation of RSR' R S R' O – + O – ++ R S R' R S R' O – sulfide •• R S R' O • • – + O • • •• – ++ •• R S R' R S R' O • • •• – sulfide sulfoxide sulfone either the sulfoxide or the sulfone can be isolated depending on the oxidizing agent and reaction conditions

Sodium metaperiodate oxidizes sulfides to sulfoxides and no further. Example •• SCH3 O • • – + •• SCH3 NaIO4 water (91%) Sodium metaperiodate oxidizes sulfides to sulfoxides and no further.

Example 1 equiv of H2O2 or a peroxy acid gives a sulfoxide, 2 equiv give a sulfone •• SCH CH2 SCH O • • •• – ++ CH2 H2O2 (2 equiv) (74-78%)

16.17 Alkylation of Sulfides: Sulfonium Salts

Sulfides can act as nucleophiles + •• •• R S + R" X R S R" X– • • R' R' product is a sulfonium salt

Example CH3I + CH3(CH2)10CH2SCH3 CH3(CH2)10CH2SCH3 I– CH3

Section 16.18 Spectroscopic Analysis of Ethers

Infrared Spectroscopy C—O stretching: 1070 and 1150 cm-1 (strong) 6

Figure 16.8 Infrared Spectrum of Dipropyl Ether CH3CH2CH2OCH2CH2CH3 C—O—C 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved. 8

H—C—O proton is deshielded by O; range is ca. d 3.3-4.0 ppm. 1H NMR H—C—O proton is deshielded by O; range is ca. d 3.3-4.0 ppm. d 1.4 ppm d 0.8 ppm d 0.8 ppm CH3 CH2 CH2 OCH2 CH2 CH3 d 3.2 ppm 6

Figure 16.9 (page 642) CH3 CH2 CH2 OCH2 CH2 CH3 1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Chemical shift (d, ppm) 1

Carbons of C—O—C appear in the range d 57-87 ppm. 13C NMR Carbons of C—O—C appear in the range d 57-87 ppm. 26.0 ppm O 68.0 ppm

UV-VIS Simple ethers have their absorption maximum at about 185 nm and are transparent to ultraviolet radiation above about 220 nm.

Mass Spectrometry Molecular ion fragments to give oxygen-stabilized carbocation. •+ CH3CH2O CHCH2CH3 m/z 102 •• CH3 + + CH3CH2O CH CH3CH2O CHCH2CH3 •• •• m/z 73 CH3 m/z 87