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Spencer L. Seager Michael R. Slabaugh www.cengage.com/chemistry/seager Chapter 13 Alcohols, Phenols, and Ethers Jennifer P. Harris ALCOHOLS, PHENOLS, & ETHERS • A hydroxy group is 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’ ALCOHOL EXAMPLES 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 NAMING ALCOHOLS (continued) • 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. CH3 OH CH3 • Example: | | | 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. NAMING PHENOLS • Substituted phenols are usually named as derivatives of the parent compound phenol. • Examples: CLASSIFICATION OF ALCOHOLS 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: PHYSICAL PROPERTIES OF ALCOHOLS (continued) • Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water. • Water interacts only with the –OH group of 1-heptanol: PHYSICAL PROPERTIES OF ALCOHOLS (continued) PHYSICAL PROPERTIES OF ALCOHOLS (continued) • The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. • Hydrogen bonding in pure ethanol: PHYSICAL PROPERTIES OF ALCOHOLS (continued) ALCOHOL REACTIONS • The removal of water (dehydration) from an alcohol at 180°C is an elimination reaction that produces an alkene. ALCOHOL DEHYDRATION TO ALKENE EXAMPLES DEHYDRATION OF AN ALCOHOL • Protonation of alcohol • Formation of carbocation and water • Formation of double bond and regeneration of catalyst ALCOHOL REACTIONS (continued) • Under slightly different conditions (140°C), a dehydration reaction can occur between two alcohol molecules to produce an ether. ALCOHOL DEHYDRATION TO ETHER EXAMPLE ALCOHOL REACTIONS (continued) • 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 ALCOHOL REACTIONS (continued) • Primary alcohol oxidation • Secondary alcohol oxidation ALCOHOL REACTIONS (continued) • Tertiary alcohol oxidation ALCOHOL OXIDATION EXAMPLES (2) After mixing, the ethanol is oxidized, and (1) The tube on the left contains orange K2Cr2O7 and is next to the colorless ethanol. chromium is reduced, forming a grayish green precipitate. ALCOHOL REACTIONS (continued) MULTISTEP REACTIONS