STRUCTURE AND SYNTHESIS OF ALCOHOLS Classification is based upon the type of carbon (primary, secondary or tertiary) bearing the OH group.
Nomenclature is as an alkanol (IUPAC) or alkyl alcohol (common). The OH bearing carbon generally gets the lower nomenclature number in preference to alkene, alkyne, alkyl or halogen. Phenols have the OH bound directly to an aromatic ring.
Hydrogen bonding affects such physical properties as water solubility and boiling point.
The O-H group is weakly acidic, comparable to so can be deprotonated by strong bases such as NaH, or can react with alkali metals in a redox reaction to generate Phenols are more acidic than alcohols due to resonance stabilization of the conjugate base over the carbons of the aromatic ring. NaOH is a strong enough base to deprotonate a phenol.
Previously learned preparations of alcohols include by hydroxide on alkyl halides (best results with primary or methyl; secondary and tertiary have competition with E2 to form alkenes instead.), acid-catalyzed hydration of alkenes (complicated sometimes by rearrangement), oxymercuration-demercuration of alkenes, hydroboration-oxidation of alkenes (producing anti-Markovnikov addition of water), and hydroxylation of alkenes to produce diols.
Syntheses of alcohols using organometallics involve the treatment of carbonyl compounds (aldehydes, ketones, esters and acyl halides) and epoxides with compounds which contain a carbon metal bond. The oppositely polarized carbons
form a carbon-carbon bond, and the oxygen of the carbonyl compound or epoxide becomes an OH group. These methods all increase the carbon content of the alcohol to be synthesized. The typical organometallics used are Grignard reagents (RMgX), alkyl lithiums (RLi) and sodium alkynides. These reagents are also very strong bases and react with any OH or NH or alkynyl C-H in an acid-base reaction.
Reduction of carbonyl compounds is another method of alcohol preparation. Aldehydes, ketones, esters and carboxylic acids can all be reduced, with the appropriate reagents, to alcohols. Catalytic hydrogenation or sodium borohydride is effective for aldehydes and ketones but not esters or carboxylic acids. Esters and acids are typically reduced with the stronger hydride reagent, lithium aluminum hydride. Thiols or mercaptans are the sulfur analogues of alcohols, containing an SH group, and can be synthesized by treating primary or secondary alkyl halides with excess NaSH, in an reaction. Thiols are more acidic than alcohols because the SH bond is weaker than the OH bond, and the conjugate base has more delocalization over the larger sulfur atom.