Unit 6 – Alcohols and Ethers Types of Alcohols Nomenclature Properties of Alcohols Synthesis of Alcohols Reactions of Alcohols

Types of Alcohols Alcohol: organic compound containing one or more hydroxyl (OH) groups. Alcohols are often classified by the type of carbinol carbon atom present the carbon bonded to the OH group Methanol wood alcohol Ethanol drinking alcohol Isopropyl alcohol rubbing alcohol

Types of Alcohols Primary alcohol: the carbinol carbon is attached to one other carbon atom Secondary alcohol: the carbinol carbon is attached to two other carbon atoms Tertiary alcohol: to three other carbon atoms

Types of Alcohols Ethylene glycol car antifreeze propylene glycol Diol: an alcohol with two OH groups Glycol: a vicinal diol OH groups on adjacent carbons Ethylene glycol car antifreeze propylene glycol medicine, food

Types of Alcohols phenol 3-methyl-1-butanethiol Phenol: a compound with a hydroxyl group bonded directly to an aromatic (benzene) ring Thiols: an organic compound with an SH group sulfur analog of alcohols also called mercaptans phenol 3-methyl-1-butanethiol

IR of Alcohols Alcohols typically exhibit a strong, broad, rounded peak at about 3300 cm-1+ for the O-H bond. SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology, 11/1/09)

IR of Alcohols In the absence of hydrogen bonding, the O – H peak can be relatively sharp and hard to distinguish from an N – H peak. The frequency for an O-H peak in the absence of hydrogen bonding is typically somewhat higher (~3600 cm-1). The O-H peak for a carboxylic acid is much broader and typically spans the distance from ~2500 – 3500 cm-1.

IR of Alcohols acid O-H acid O-H alcohol O-H w/hydrogen bonding alcohol O-H w/o hydrogen bonding

Nomenclature a substituted pentanol IUPAC Naming System for Alcohols: Find the longest continuous chain that contains the carbinol carbon atom Drop the “e” from the corresponding alkane name and add the suffix “ol” a substituted pentanol

Nomenclature (2R, 3R)-3-methyl-2-pentanol IUPAC Naming System for Alcohols: Number the longest chain starting from the end closest to the OH group. OH takes priority over double and triple bonds OH group is assumed to be on C #1 on a cycloalkane ring Name and number all substituents as with an alkane or alkene. Don’t forget R or S if appropriate. (2R, 3R)-3-methyl-2-pentanol

Nomenclature 4-methyl-5-hexen-1-ol 4-methylhex-5-en-1-ol To name an alcohol that contains a double bond: use “ol” suffix after the name of the alkene (drop the last “e”) number the chain to give the carbinol carbon the lowest possible number place the position number for the C=C in front of the base name (or before the “en”) and the position number for the OH in front of the “ol” suffix 4-methyl-5-hexen-1-ol 4-methylhex-5-en-1-ol

Nomenclature 2, 3-pentanediol or pentane-2, 3-diol To name diols: use suffix “diol” after the name of the alkane (keep the ending “e”) indicate the position of each OH group place position of each OH group in front of the base name or in front of the suffix “diol” 2, 3-pentanediol or pentane-2, 3-diol

Nomenclature 2-pentanethiol 3-methyl-2-pentanethiol To name thiols: Use the same rules for naming alcohols use “thiol” suffix instead of “ol” suffix 2-pentanethiol 3-methyl-2-pentanethiol

Nomenclature Common names are often used with phenols: 2-bromophenol or ortho-bromophenol phenol 3-nitrophenol or meta-nitrophenol 4-chlorophenol or para-chlorophenol ortho = 1,2 meta = 1,3 para = 1,4

Nomenclature Common names are often used with phenols: 2-methylphenol ortho-cresol 4-methylphenol para-cresol Benzene-1,2-diol catechol Benzene-1,3-diol resorcinol Benzene-1,4-diol hydroquinone

Nomenclature Example: Name the following compounds:

Nomenclature Example: Draw the structures of the following compounds. 3-isopropyl-2-methyl-2-hexanol trans-2-bromocyclohexanol (E)-2-chloro-2-buten-1-ol

Properties of Alcohols The physical properties of alcohols are strongly influenced by the presence of the hydrophilic (“water loving”) OH group. The OH group is capable of forming hydrogen bonds with other alcohol groups or with water.

Properties of Alcohols Due to hydrogen bonding, alcohols have significantly higher boiling points than alkanes with comparable molecular weights. CH3CH2OH MW = 46 BP = 78oC CH3CH2CH3 MW = 44 BP = - 42oC

Properties of Alcohols BP increases as the amount of hydrogen bonding increases: 1-propanol BP = 97oC 1,2-propanediol BP = 188oC (propylene glycol) 1,2,3-propanetriol BP = 290oC (Glycerol)

Physical Properties Alcohols with 1-3 carbons are soluble in water.

Properties of Alcohols Solubility decreases as the size of the alkyl group increases. 1-hexanol is less soluble than ethanol Solubility increases as the alkyl group becomes more compact/spherical. t-butyl alcohol is more soluble than 1-butanol. Solubility increases with increasing number of OH groups.

Acidity of Alcohols and Phenols The acidity of alcohols varies widely and can be expressed using the acid dissociation constant, Ka ROH + H2O RO- + H3O+ Ka = [RO-][H3O+] pKa = -log Ka [ROH] Acidity increases as: Ka increases pKa decreases Alkoxide ion

Acidity of Alcohols and Phenols Structural trends and acidity: Acidity of H2O, CH3OH, and CH3CH2OH are similar. (pKa = 15.7, 15.5, and 15.9 respectively) Acidity decreases as number of carbons in the R group increases. CH3OH pKa = 15.5 t-butyl alcohol pKa = 18.0

Acidity of Alcohols and Phenols Structural trends and acidity: Acidity increases with the addition of electron-withdrawing halogens pKa = 14.3 pKa = 12.2 pKa = 15.9

Acidity of Alcohols and Phenols Structural trends and acidity: Phenols are more acidic than water or alcohols pKa = 18.0 pKa = 10.0

Acidity of Alcohols and Phenols Phenols are stronger acids than alcohols. React readily with aqueous NaOH Phenols are soluble in aqueous strong base solutions but are insoluble in aqueous NaHCO3. + Sodium phenoxide

Acidity of Alcohols and Phenols Since alcohols are very weak acids, a very strong base is used to remove the acidic proton. Unless they are water soluble, alcohols are not soluble in aqueous base solution.

Synthesis of Alcohols Nucleophilic Substitution on an alkyl halide SN2 conditions most useful strong nucleophile methyl > 1o > 2o inversion of configuration

Synthesis of Alcohols Acid Catalyzed Hydration (Hydrolysis) of Alkenes Markovnikov product formed Equilibrium process Less useful synthetically than other methods rearrangements often occur

Synthesis of Alcohols Oxymercuration-Demercuration of Alkenes Markovnikov product Anti addition to double bond

Synthesis of Alcohols Hydroboration-Oxidation of Alkenes Anti-Markovnikov product Syn addition to double bond

Synthesis of Alcohols or Syn Hydroxylation of Alkenes Syn addition to double bond Reagents: OsO4, H2O2 cold, dilute KMnO4, OH- or

Synthesis of Alcohols Anti-Hydroxylation of Alkenes epoxide intermediate Anti addition to double bond Common peroxyacids: CH3CO3H MCPBA