Organic Chemistry,William H. Brown Christopher S. Foote Brent L. Iverson,Alcohols and Thiols,Chapter 10,Structure - Alcohols,The functional group of an alcohol is an -OH group bonded to an sp3 hybridized carbon bond angles about the hydroxyl oxygen atom are approximately 109.5 Oxygen is sp3 hybridized two sp3 hybrid orbitals form sigma bonds to carbon and hydrogen the remaining two sp3 hybrid orbitals each contain an unshared pair of electrons,Nomenclature-Alcohols,IUPAC names the parent chain is the longest chain that contains the OH group number the parent chain to give the OH group the lowest possible number change the suffix -e to -ol Common names name the alkyl group bonded to oxygen followed by the word alcohol,Nomenclature-Alcohols,Examples,Nomenclature of Alcohols,Compounds containing more than one OH group are named diols, triols, etc.,Nomenclature of Alcohols,Unsaturated alcohols show the double bond by changing the infix from -an- to -en- show the the OH group by the suffix -ol number the chain to give OH the lower number,Physical Properties,Alcohols are polar compoundsthey interact with themselves and with other polar compounds by dipole-dipole interactions Dipole-dipole interaction: the attraction between the positive end of one dipole and the negative end of another,Physical Properties,Hydrogen bonding: when the positive end of one dipole is an H bonded to F, O, or N (atoms of high electronegativity) and the other end is F, O, or N the strength of hydrogen bonding in water is approximately 21 kJ (5 kcal)/mol hydrogen bonds are considerably weaker than covalent bonds nonetheless, they can have a significant effect on physical properties,Hydrogen Bonding,Physical Properties,Ethanol and dimethyl ether are constitutional isomers. Their boiling points are dramatically different ethanol forms intermolecular hydrogen bonds which increase attractive forces between its molecules resulting in a higher boiling point there is no comparable attractive force between molecules of dimethyl ether,bp -24C,Ethanol,Dimethyl ether,Physical Properties,In relation to alkanes of comparable size and molecular weight, alcohols have higher boiling points are more soluble in water The presence of additional -OH groups in a molecule further increases solubility in water and boiling point,Physical Properties,Acidity of Alcohols,In dilute aqueous solution, alcohols are weakly acidic,Acidity of Alcohols,Acidity of Alcohols,Acidity depends primarily on the degree of stabilization and solvation of the alkoxide ion the negatively charged oxygens of methanol and ethanol are about as accessible as hydroxide ion for solvation; these alcohol are about as acidic as water as the bulk of the alkyl group increases, the ability of water to solvate the alkoxide decreases, the acidity of the alcohol decreases, and the basicity of the alkoxide ion increases,Reaction with Metals,Alcohols react with Li, Na, K, and other active metals to liberate hydrogen gas and form metal alkoxidesAlcohols are also converted to metal alkoxides by reaction with bases stronger than the alkoxide ion one such base is sodium hydride,Reaction with HX,3 alcohols react very rapidly with HCl, HBr, and HIlow-molecular-weight 1 and 2 alcohols are unreactive under these conditions 1 and 2 alcohols require concentrated HBr and HI to form alkyl bromides and iodides,Reaction with HX,with HBr and HI, 2 alcohols generally give some rearranged product1 alcohols with extensive -branching give large amounts of rearranged product,Reaction with HX,Based on the relative ease of reaction of alcohols with HX (3 2 1) and the occurrence of rearrangements, Chemists propose that reaction of 2 and 3 alcohols with HX occurs by an SN1 mechanism, and involves a carbocation intermediate,Reaction with HX - SN1,Step 1: proton transfer to the OH group gives an oxonium ionStep 2: loss of H2O gives a carbocation intermediate,Reaction with HX - SN1,Step 3: reaction of the carbocation intermediate (an electrophile) with halide ion (a nucleophile) gives the product,Reaction with HX - SN2,1 alcohols react with HX by an SN2 mechanism Step 1: rapid and reversible proton transferStep 2: displacement of HOH by halide ion,Reaction with HX,For 1 alcohols with extensive -branching SN1 is not possible because this pathway would require a 1 carbocation SN2 is not possible because of steric hindrance created by the -branching These alcohols react by a concerted loss of HOH and migration of an alkyl group,Step 1: proton transfer gives an oxonium ionStep 2: concerted elimination of HOH and migration of a methyl group gives a 3 carbocation,Reaction with HX,Reaction with HX,Step 3: reaction of the carbocation intermediate (an electrophile) with halide ion (a nucleophile) gives the product,Reaction with PBr3,