MCAT Organic Chemistry > Alcohols
An alcohol is any oxygen containing organic compound with the general formula R-OH.
Alcohols are either given the prefix hydroxyl or hydroxy.
Alcohols are named in the IUPAC system by replacing the –e ending of the root alkane with the ending –ol. The carbon atom attached to the hydroxyl group must be included in the longest chain and receives the lowest possible number.
Alternatively, the alkyl group can be named as a derivative, followed by the word alcohol, e.g. ethyl alcohol, isobutyl alcohol.
Boiling points of alcohols are significantly higher than those of structurally isomeric hydrocarbons due to hydrogen bonding.
Molecules with more than one hydroxyl (-OH) group show increased levels of hydrogen bonding.
Learn the pKas of alcohols. Phenyl alcohols, or phenols, are more acidic than normal alcohols.
Alcohols are usually water soluble if they are not attached to a hydrophobic molecule.
Hydrogen bonding is the main reason alcohols tend to have higher boiling points analogous organic compounds.
The table below compares the acidity of alcohols with other groups of oxygen-containing compounds.
A lower pka denotes a higher acidity to the compound.
|-CH2(CO)-R||Aldehydes and Ketones||20|
|-CH2(CO)-OR||Keto Acids and Esters||25|
Additional branching on an alcohol will decrease the melting point and boiling point.
The infrared spectroscopy of the OH group occurs around 3300 cm-1 due to the high energy hydrogen bond.