Lecture 4 - Aromatics - BME 201 Suggested problems review...

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1 BME 201 Suggested problems review material: Vollhardt, 6 th Ed., Chapter 9, problems no. 56,57,58; new reactions and important concepts on page 374-377; reactions of alcohols on page 378, chapter 15, exercises 15-1, 15-2, 15-3, 15-4, “The big picture” on page 717 (aromaticity), selected “important concepts” on page 722. Todays lecture is based on Vollhardt, selected materials from chapter 9 ( ethers and thiols, alcohols ), chapter 15 ( aromatics ), chapter 22 ( phenols ) as well as materials mentioned on other selected handouts. Handouts may have marked chapter numbers and page numbers for suggested reading. You will find it easier to do the suggested problems and pass future quizzes and exams if you go over the reading prior to attempting to solve the suggested problems.
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2 Sulfur Analogs of Alcohols and Ethers
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3 Sulfur Analogs of Alcohols and Ethers 9-10 The sulfur analogs of alcohols and ethers are thiols and sulfides. The IUPAC system calls the sulfur analogs of alcohols, R-SH, “thiols.” The –SH group in more complicated compounds is referred to as “mercapto.”
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4 The sulfur analogs of ethers are called “sulfides” (common name, thioethers). The RS group is called “alkylthio,” and the RS - group is called “alkanethiolate.”
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5 Thiols are less hydrogen-bonded and more acidic than alcohols. Compared to oxygen, sulfur has a large size, diffuse orbitals and a relatively nonpolarized S-H bond. The boiling points of thiols are similar to those of the analogous haloalkanes.
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6 Thiols are more acidic than water and can therefore be easily deprotonated by hydroxide and alkoxide ions:
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7 Thiols and sulfides react much like alcohols and ethers. The sulfur in thiols and sulfides is more nucleophilic than the oxygen in the analogous compounds . Thiols and sulfides are readily made through nucleophilic attack by RS - or HS - on haloalkanes:
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8 Sulfides are prepared by the alkylation of thiols in the presence of a base, such as hydroxide. The nucleophilicity of the generated thiolates is much greater than that of hydroxide which eliminates the competing S N 2 substitution by hydroxide ion.
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9 Sulfides can attack haloalkanes to form sulfonium ions. Sulfonium ions are subject to nucleophilic attack, the leaving group being a sulfide.
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10 Valence-shell expansion of sulfur accounts for the special reactivity of thiols and sulfides. Sulfur can expand its valence shell from 8 to 10 or 12 electrons using its available 3d orbitals, allowing oxidation states not available to its oxygen analogs.
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11 Milder oxidizing agents (I 2 ) yield disulfides . These can be reduced back to thiols by alkali metals. Reversible disulfide formation is important in stabilizing the folding of biological enzymes:
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12 Sulfides can also be oxidized to sulfoxides and then sulfones:
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13 Physiological Properties and Uses of Alcohols and Ethers
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Physiological Properties and Uses of Alcohols and Ethers 9-11 Methanol: Formed by catalytic reduction of CO and H 2 at high temperatures and pressure. Used as a
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This note was uploaded on 02/20/2012 for the course BME 201 taught by Professor Schmidt during the Fall '11 term at Purdue University-West Lafayette.

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Lecture 4 - Aromatics - BME 201 Suggested problems review...

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