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Chapter 13 Alcohols, Phenols, and Thiols 13.1 Alcohols, Phenols, and Thiols Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Alcohols and Phenols An alcohol contains • A hydroxyl group (—OH) attached to a carbon chain. A phenol contains • A hydroxyl group (—OH) attached to a benzene ring. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Classification of Alcohols Alcohols are classified • By the number of alkyl groups attached to the carbon bonded to the hydroxyl. • As primary (1°), secondary (2°), or tertiary (3°). Primary (1º) 1 group H | CH3—C—OH | H Secondary (2º) 2 groups CH3 | CH3—C—OH | H Tertiary (3º) 3 groups CH3 | CH3—C—OH | CH3 Learning Check Classify each alcohol as (P) primary, (S) secondary, or (T) tertiary. OH | 1. CH3—CH—CH2—CH3 2. CH3—CH2—CH2—OH OH | 3. CH3—CH2—C—CH2—CH3 | CH3 Solution OH | 1. CH3—CH—CH2—CH3 (S) secondary 2. CH3—CH2—CH2—OH (P) primary OH | 3. CH3—CH2—C—CH2—CH3 CH3 (T) tertiary Naming Alcohols The names of alcohols • In the IUPAC system replace -e of alkane name with -ol. • that are common names use the name of the alkyl group followed by alcohol. Formula IUPAC Common Name CH4 methane CH3─OH methanol CH3─CH3 ethane CH3─CH2─OH ethanol methyl alcohol ethyl alcohol More Names of Alcohols In IUPAC names for longer carbon chains, the chain is numbered from the end nearest the ─OH group. CH3─CH2─CH2─OH 1-propanol OH │ CH3─CH─CH2─CH3 2-butanol CH3 OH │ │ CH3─CH─CH2─CH2─CH─CH3 6 5 4 3 2 1 5-methyl-2-hexanol Some Typical Alcohols OH | “rubbing alcohol” CH3—CH—CH3 2-propanol (isopropyl alcohol) antifreeze HO—CH2—CH2—OH 1,2-ethanediol (ethylene glycol) glycerol OH OH | HO—CH2—CH—CH2— Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 1,2,3-propanetriol Learning Check Give the IUPAC name for each of the following: 1. CH3—CH2—CH2—CH2—OH OH CH3 | | 2. CH3—CH—CH—CH2—CH3 OH 3. Solution 1. CH3—CH2—CH2—CH2—OH 1-butanol OH CH3 | | 2. CH3—CH—CH—CH2—CH3 3-methyl-2-pentanol 3. OH cyclopentanol Learning Check Write the structure of the following: A. 3-pentanol B. ethyl alcohol C. 3-methylcyclohexanol Solution Write the structure of the following: A. 3-pentanol OH | CH3—CH2—CH—CH2—CH3 B. ethyl alcohol CH3 —CH2 —OH C. 3-methylcyclohexanol OH CH 3 Phenols in Medicine Phenol • Is the IUPAC name for benzene with a hydroxyl group. • Is used in antiseptics and disinfectants. OH OH OH OH OH CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 phenol resorcinol 4-hexylresorcinol Derivatives of Phenol • Compounds of phenol are the active ingredients in the essential oils of cloves, vanilla, nutmeg, and mint. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Name each of the following compounds: OH | A. CH3—CH2 —CH—CH3 CH3 | B. CH3—CH2—CH—CH2—CH2—OH C. CH3—CH2—CH2—SH Solution Name each of the following compounds: OH | A. CH3—CH2 —CH—CH3 2-butanol CH3 | B. CH3—CH2—CH—CH2—CH2—OH 3-methyl-1-pentanol C. CH3—CH2—CH2—SH 1-propanethiol Chapter 13 Alcohols, Phenols, Ethers, and Thiols 13.2 Ethers Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Ethers Ethers • Contain an ─O─ between two carbon groups. • That are simple are named by listing the alkyl names in alphabetical order followed by ether CH3─O─CH3 CH3─CH2─O─CH3 IUPAC Names for Ethers • In the IUPAC system, the shorter alkyl group and the oxygen are named as an alkoxy group attached to the longer alkane. methoxy propane CH3—O—CH2—CH2—CH3 1 2 3 • Numbering the longer alkane gives 1-methoxypropane Ethers as Anesthetics Anesthetics • Inhibit pain signals to the brain. • Such as ethyl ether CH3─CH2─O─CH2─CH3 were used for over a century, but caused nausea and were flammable. • Developed by 1960s were nonflammable. Cl F F Cl F H │ │ │ │ │ │ H─C─C─O─C─H H─C─C─O─C─H │ │ │ │ │ │ F F F H F H Ethane(enflurane) Penthrane MTBE Methyl tert-butyl ether CH3 │ CH3─O─C─CH3 │ CH3 • Is one of the most produced organic chemicals. • Is a fuel additive • Is used to improve gasoline combustion. • Use is questioned since the discovery that MTBE has contaminated water supplies. Learning Check Draw the structure of each compound. A. diethyl ether B. ethyl methyl ether C. 2-methoxybutane Solution Draw the structure of each compound. A. diethyl ether CH3—CH2—O—CH2—CH3 B. ethyl methyl ether CH3—CH2—O—CH3 C. 2-methoxybutane O—CH3 | CH3—CH—CH2—CH3 Cyclic Ethers A cyclic ether • Contains an O atom in a carbon ring. • Is called a heterocyclic compound. • Typically has 5 (furan) or 6 atoms (pyran) in the ring. O O furan O tetrahydrofuran O O pyran 1,4-dioxane Dioxins Dioxins are • A group of ethers that are highly toxic. • Formed during forest fires and as industrial by-products. • Often carcinogenic. O Cl O Cl Cl CH 2 C OH 2,4,5-trichlorophenoxyacetic acid (2,4,5-T; agent orange) Cl O Cl Cl O Cl 2,3,7,8-tetrachlorodibenzodioxin (TTCC, “dioxin”) Learning Check Name each of the following: O 1. O 2. O CH 3 Solution 1. O 2. O O CH 3 methoxy cyclopentane (cyclopentyl methyl ether) 1,4-dioxane Chapter 13 Alcohols, Phenols, Ethers, and Thiols 13.3 Physical Properties of Alcohols, Phenols, and Ethers Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Boiling Points of Alcohols Alcohols • Contain a strongly electronegative O in the OH groups. • Form hydrogen bonds between alcohol molecules. • Have higher boiling points than alkanes and ethers of similar mass. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Boiling Points of Ethers Ethers • Have an O atom, but no H is attached. • Cannot form hydrogen bonds between ether molecules. • Have boiling points similar to alkanes of similar mass. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Solubility of Alcohols and Ethers in Water • Alcohols and ethers are more soluble in water than alkanes because the oxygen atom hydrogen bonds with water. • Alcohols with 1-4 C atoms are soluble, but alcohols with 5 or more C atoms are not. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Comparing Solubility and Boiling Points Compound Alkane CH3─CH2─CH3 Ether CH3─O─CH3 Alcohol CH3─CH2─OH Molar Mass 44 Boiling Point (°C) -42 Soluble in Water? No 46 -23 Yes 46 78 Yes Solubility of Phenol Phenol • Is soluble in water. • Has a hydroxyl group that ionizes slightly (weak acid). • Is corrosive and irritating to the skin. OH O- + H2O + H3O+ Learning Check Which compound would have the higher boiling point? Explain. ethyl methyl ether or 1-propanol Solution 1-propanol would have the higher boiling point because an alcohol can form hydrogen bonds, but the ether cannot. Learning Check Which compound would be more soluble in water? Explain. ethanol or 2-pentanol Solution Ethanol. An alcohol with two carbons in its carbon chain is more soluble than one with 5 carbons. The longer alkyl chain diminishes the effect of the –OH group. Chapter 13 Alcohols, Phenols, Ethers, and Thiols Reactions of Alcohols and Thiols Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Combustion of Alcohols Combustion is the reaction of an alcohol with O2 to produce CO2 and H2O. 2CO2 + 4H2O + Heat 2CH3OH + 3O2 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Dehydration of Alcohols Dehydration of an alcohol occurs • When heated with an acid catalyst. • With the loss of —H and —OH from adjacent carbon atoms. H OH H+, heat | | H—C—C—H H—C=C—H + H2O | | | | H H H H alcohol alkene Learning Check Write the equations for the reactions when 2-propanol undergoes: 1. combustion 2. dehydration Solution OH │ CH3─CH─CH3 = 2-propanol = C3H8O 1. combustion 2C3H8O + 9O2 2. dehydration OH │ CH3─CH─CH3 6CO2 + 8H2O H+ CH3─CH=CH2 + H2O Formation of Ethers • Ethers form when dehydration takes place at low temperature. H+ CH3—OH + HO—CH3 CH3—O—CH3 + H2O two methanol dimethyl ether Oxidation and Reduction In the oxidation of an organic compound • There is an increase in the number of C—O bonds. • There is a loss of H. In the reduction of an organic compound • There is an decrease in the number of C—O bonds. • There is a gain of H. Oxidation and Reduction ERROR: stackunderflow OFFENDING COMMAND: ~ STACK: