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Alcohols Alcohols and Phenols • Organic compound containing one or more hydroxyl groups, (-OH). General formula R-OH. Space-filling models for the three simplest unbranched-chain alcohols: methyl alcohol, ethyl alcohol, and propyl alcohol. Naming Alcohols Step 1: Name the longest chain to which the – OH group is attached. Use the alkane name of the chain, drop the –e ending, and replace it with –ol. Step 2: Number the longest chain to give the lowest number to the carbon with the –OH. Step 3: Locate the –OH position. Example: Ethanol OH | CH3—CH2—CH2—CH—CH2—CH3 6 5 4 3 2 1 propanol Methanol 3-hexanol Naming Alcohols, cont. 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. Name the Following: OH 1. OH 2. 3. Example: 4. CH3 OH CH3 | | | CH3—CH2—CH2—CH—CH—CH3 6 5 4 3 2 1 HO OH 2,4-dimethyl-3-hexanol 1 Naming Alcohols, cont. Name the Following: Step 6: Compounds containing more than one hydroxyl groups are called glycols and are named by adding di, tri, etc… before the –ol suffix of the parent chain name. OH 1. OH HO OH 2. OH Example: 3. OH CH3 OH CH3 | | | | CH3—CH2—CH2—CH—CH—CH3 1 2 3| 4 5 6 OH 4. HO OH HO 3,5-dimethyl-2,3,4-hexantriol Naming Alcohols, cont. Alkyl Nomenclature: Short chained alcohols are commonly named as alkyl substituents on a hydroxyl parent chain. •To name alcohols according to alkyl nomenclature, treat the –OH group as the parent chain and name the alkyl substituent followed by the word alcohol. OH Example: CH3-CH2-OH ethyl alcohol OH Name the Following (giving both IUPAC and alkyl nomenclature when possible): 1. 2. OH OH OH 3. OH 4. OH OH 5. OH iso-propyl alcohol 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: Why are there no quaternary alcohols? 2 Solubility Physical Properties of Alcohols, cont. •Solubilities in water of selected primary (1o) alcohols. Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water. Water interacts only with the hydrophilic –OH group of 1-heptanol: •Notice as chain length increases, solubility decreases Physical Properties of Alcohols, cont. Space-filling molecular models showing the nonpolar (green) and polar (pink) parts of methanol and 1-octanol. The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. Hydrogen bonding in pure ethanol: Boiling Points •Boiling points of selected primary (1o) alcohols compared to alkanes and ethers of similar molecular weights •Notice B.P.’s increase with increasing M.W. Important Alcohols: Methanol Methanol (Wood alcohol) CH3OH. Production: Useful as a solvent and industrial starting material. Highly toxic, causes blindness and/or death. 3 Important Alcohols, cont. Ethanol 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). found in alcoholic beverages. Moderately toxic. Important Alcohols, cont. 2-propanol (isopropyl isopropyl alcohol) alcohol is the main component of rubbing alcohol. OH Important Alcohols, cont. Antifreezes/deicers ethylene glycol). 1,2-ethanediol (ethylene glycol 1,2,3-propanetriol (glycerol glycerol) glycerol is used as a food moistening agent (nontoxic) and for its soothing qualities (soaps). CH3 – CH -- CH2 OH OH OH Alcohols vs. Phenols Alcohol – has an –OH group attached to an aliphatic carbon. General formula ROH. Phenol – has an –OH group on a benzene ring. Naming Phenols as the Parent Chain Step 1: Identify all substituents and number from the hydroxyl group (1) to give all substituents the lowest possible designation Step 2: name all substituents in alphabetical order * ortho-, meta-, and para-, designations may be used for phenols with only one additional substituent. Example: OH 3-methyl phenol Or m-methyl phenol 4 Naming Phenols as a Substituent Step 1: Identify the parent chain, numbering according to rules for alkanes, -enes, or alcohols. Step 2: list all substituents in alphebetical order with positions, including phenols. *use ortho-, meta-, and paradesignations to describe the position of the hydroxyl in respect to the bond to the parent chain. 2,3-dimethyl-5-mphenol heptane Example: OH Name the Following: 1. 2. OH OH OH OH 3. 4. Cl OH OH OH 5. OH Uses of Phenols: In a dilute solution, phenol is a disinfectant. Phenol derivatives used as disinfectants o-phenylphenol 2-benzyl-4-chlorophenol Phenol derivatives used as antioxidants in food as preservatives BHA (butylated hydroxy anisole) BHT (butylated hydroxy toluene) 5