alcohol

(noun)

Class of organic compounds containing a hydroxyl functional group.

Related Terms

Examples of alcohol in the following topics:

  • Reactions of Alcohols

    • Alcohols can undergo elimination, but only by E1.
    • The acid protonates the alcohol to make it a good leaving group, then the halide displaces the alcohol with nucleophilic attack on the electrophilic carbon.
    • Although tertiary alcohols cannot be oxidized, secondary alcohols can be converted to ketones using an oxidizing agent.
    • On the left, a tertiary alcohol undergoes an SN1 reaction.
    • On the right, a primary alcohol undergoes an SN2 reaction.

  • Alcohols

    • Alcohols are functional groups characterized by the presence of an -OH group.
    • Alcohols are an important class of molecules with many scientific, medical, and industrial uses.
    • The structure of an alcohol is similar to that of water, as it has a bent shape.
    • Alcohols are able to participate in many chemical reactions.
    • Alcohols have many uses in our everyday world.

  • Alcohol Reactions

    • The functional group of the alcohols is the hydroxyl group, –OH.
    • Indeed, the dipolar nature of the O–H bond is such that alcohols are much stronger acids than alkanes (by roughly 1030 times), and nearly that much stronger than ethers (oxygen substituted alkanes that do not have an O–H group).
    • The most reactive site in an alcohol molecule is the hydroxyl group, despite the fact that the O–H bond strength is significantly greater than that of the C–C, C–H and C–O bonds, demonstrating again the difference between thermodynamic and chemical stability.

  • Oxidation of Alcohols by DMSO

    • One source of oxygen that has proven effective for the oxidation of alcohols is the simple sulfoxide solvent, DMSO.
    • The reaction is operationally easy: a DMSO solution of the alcohol is treated with one of several electrophilic dehydrating reagents (E).
    • The alcohol is oxidized; DMSO is reduced to dimethyl sulfide; and water is taken up by the electrophile.
    • Bonding of sulfur to the alcohol oxygen atom then follows.
    • The remaining steps are eliminations, similar in nature to those proposed for other alcohol oxidations.

  • Nucleophilic Substitution of the Hydroxyl Group

    • As was true for alkyl halides, nucleophilic substitution of 1º-alcohols proceeds by an SN2 mechanism, whereas 3º-alcohols react by an SN1 mechanism.
    • Alcohols having acid sensitive groups would, of course, not tolerate such treatment.
    • Phosphorous tribromide is best used with 1º-alcohols, since 2º-alcohols often give rearrangement by-products resulting from competing SN1 reactions.
    • The last example shows the reaction of thionyl chloride with a chiral 2º-alcohol.
    • This aspect of alcohol chemistry will be touched upon in the next section.

  • Elimination Reactions of Alcohols

    • Most alcohols are slightly weaker acids than water so the left side is favored.
    • The elimination of water from an alcohol is called dehydration.
    • This procedure is also effective with hindered 2º-alcohols, but for unhindered and 1º-alcohols an SN2 chloride ion substitution of the chlorophosphate intermediate competes with elimination.
    • The first equation shows the dehydration of a 3º-alcohol.
    • The second example shows two elimination procedures applied to the same 2º-alcohol.

  • Alcohol Nomenclature

    • Alcohols are usually named by the first procedure and are designated by an ol suffix, as in ethanol, CH3CH2OH (note that a locator number is not needed on a two-carbon chain).
    • For the mono-functional alcohols, this common system consists of naming the alkyl group followed by the word alcohol.
    • Alcohols may also be classified as primary, 1º, secondary, 2º & tertiary, 3º, in the same manner as alkyl halides.
    • The chemistry of thiols will not be described here, other than to note that they are stronger acids and more powerful nucleophiles than alcohols.

  • Preparation of Ethers

    • Ethers are usually prepared from alcohols or their conjugate bases.
    • Note that the alcohol reactant is used as the solvent, and a trifluoroacetate mercury (II) salt is used in preference to the acetate (trifluoroacetate anion is a poorer nucleophile than acetate).
    • The mechanism of alkoxymercuration is similar to that of oxymercuration, with an initial anti-addition of the mercuric species and alcohol being followed by reductive demercuration.
    • Acid-catalyzed dehydration of small 1º-alcohols constitutes a specialized method of preparing symmetrical ethers.
    • At 110º to 130 ºC an SN2 reaction of the alcohol conjugate acid leads to an ether product.

  • Boiling Point and Water Solubility

    • It is instructive to compare the boiling points and water solubility of amines with those of corresponding alcohols and ethers.
    • The dominant factor here is hydrogen bonding, and the first table below documents the powerful intermolecular attraction that results from -O-H---O- hydrogen bonding in alcohols (light blue columns).
    • Alkanes provide reference compounds in which hydrogen bonding is not possible, and the increase in boiling point for equivalent 1º-amines is roughly half the increase observed for equivalent alcohols.
    • The water solubility of 1º and 2º-amines is similar to that of comparable alcohols.
    • The basicity of amines (next section) allows them to be dissolved in dilute mineral acid solutions, and this property facilitates their separation from neutral compounds such as alcohols and hydrocarbons by partitioning between the phases of non-miscible solvents.

  • Waxes

    • Waxes are esters of fatty acids with long chain monohydric alcohols (one hydroxyl group).
    • The formulas for three well known waxes are given below, with the carboxylic acid moiety colored red and the alcohol colored blue.