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Chapter 13: Alcohols, Phenols, and Ethers 1 ALCOHOLS, PHENOLS, AND ETHERS • Hydroxy group – the –OH functional group • An alcohol has an –OH group attached to an aliphatic carbon. General formula: R-OH • A phenol has an –OH group on a benzene ring. • An ether has the functional group: General formula: R-O-R’ 2 NAMING ALCOHOLS Step 1: Name the longest chain to which the –OH group is attached. Use the hydrocarbon name of the chain, drop the final –e, and replace it with –ol. Step 2: Number the longest chain to give the lowest number to the carbon with the attached –OH. Step 3: Locate the –OH position. Example: OH | CH3—CH2—CH2—CH—CH2—CH3 6 5 4 3 2 1 3-hexanol 3 Step 4: Locate and name any other groups attached to the longest chain. Step 5: Combine the name and location of other groups, the location of the –OH, and the longest chain into the final name. Example: CH3 OH CH3 | | | CH3—CH2—CH—CH—CH—CH3 6 5 4 3 2 1 2,4-dimethyl-3-hexanol Note: Alcohols containing two –OH groups are diols, three –OH groups are triols. The IUPAC names for these compounds have endings of –diol and –triol rather than –ol. 4 NAMING PHENOLS • Substituted phenols are usually named as derivatives of the parent compound phenol. Examples: 5 CLASSIFICATION OF ALCOHOLS 6 PHYSICAL PROPERTIES OF ALCOHOLS • The –OH group is polar and capable of hydrogen bonding. • This makes low molecular weight alcohols highly soluble in water. • Hydrogen bonding in a water-methanol solution: 7 PHYSICAL PROPERTIES OF ALCOHOLS, cont. • Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water. • Water interacts only with the –OH group of 1-heptanol: 8 PHYSICAL PROPERTIES OF ALCOHOLS, cont. 9 PHYSICAL PROPERTIES OF ALCOHOLS, cont. • The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. • Hydrogen bonding in pure ethanol: 10 PHYSICAL PROPERTIES OF ALCOHOLS, cont. 11 ALCOHOL REACTIONS The removal of water (dehydration) from an alcohol at 180°C is an elimination reaction that produces an alkene. 12 ALCOHOL REACTIONS, cont. • Under slightly different conditions (140°C), a dehydration reaction can occur between two alcohol molecules to produce an ether. 13 ALCOHOL REACTIONS, cont. • Oxidation – the removal of hydrogen atoms. • Alcohol oxidations with an oxidizing (O) agent, such as K2Cr2O7 and KMnO4: • Primary alcohols aldehyde carboxylic acid • Secondary alcohols ketone • Tertiary alcohols no reaction 14 ALCOHOL REACTIONS, cont. • Primary alcohol oxidation • Secondary alcohol oxidation 15 IMPORTANT ALCOHOLS • Methanol (wood alcohol): CH3OH • Production: •Useful as a solvent and industrial starting material • Highly toxic, if taken internally causes blindness and/or death 16 IMPORTANT ALCOHOLS, cont. • Ethanol (ethyl alcohol, grain alcohol): CH3CH2OH • Produced commercially from ethylene and through biological (yeast) fermentation of carbohydrates • Useful as a solvent, industrial starting material, fuel (gasohol), and found in alcoholic beverages. • Moderately toxic 17 IMPORTANT ALCOHOLS, cont. • 2-propanol (isopropyl alcohol) is the main component of rubbing alcohol • 1,2,3-propanetriol (glycerol) is used as a food moistening agent (nontoxic) and for its soothing qualities (soaps) 18 IMPORTANT ALCOHOLS, cont. • Antifreezes 1,2-ethanediol (ethylene glycol) 1,2-propanediol (propylene glycol) 19 PHENOLS • Phenol behaves as a weak acid in water and can react with bases to form salt. 20 USES OF PHENOLS: • In a dilute solution, phenol is used as a disinfectant. • Phenol derivatives used as disinfectants: 21 USES OF PHENOLS: • Phenol derivatives used as antioxidants in food: 22 PROPERTIES OF ETHERS • Much less polar than alcohols • More soluble in water than alkanes, but less soluble than alcohols • Low boiling and melting points because of the inability to hydrogen bond between molecules • inert and do not react with most reagents (like alkanes) • highly flammable (like alkanes) 23 • Hydrogen bonding of dimethyl ether: (a) with water and (b) no hydrogen bonding in the pure state: 24 THIOLS: THE –SH (SULFHYDRYL) GROUP • Most distinguishing characteristic is their strong and offensive odor • ethanethiol – added to natural gas • 1-propanethiol – odor in garlic and onions • trans-2-butene-1-thiol – odor associated with skunks 25 THIOL REACTIONS • Oxidation forms disulfide (-S-S-) linkages, which are important structural features of some proteins: 26 THIOL REACTIONS, cont. • Oxidation reactions can be reversed with a reducing agent (H): 27 POLYFUNCTIONAL COMPOUNDS • Compounds with two or more functional groups • Functional groups determine chemical properties of compounds. Example: 28