At low pH, or when surrounded by strong acids, they may be protonated to alkyloxonium ions. However, as the hydrocarbon chain increases beyond butanol to pentanol and hexanol, alcohols become virtually immiscible in water.Īlcohols are amphoteric species that may exist as both acids and bases. In a small molecule such as propanol, the alcohol dissolves because the polar alcohol group outweighs the very short hydrogen chain. The hydrocarbon portion of the alcohol is nonpolar, and thus resists dissolving in water the polar alcohol group is hydrophilic and thereby promotes dissolution in water. The solubility of alcohols in water is interesting because alcohols have hydrophobic and hydrophilic centers, making them amphipathic or amphiphilic. Alcohols also have higher boiling points than the hydrocarbons and ethers which contain a comparable number of carbon atoms. The ability of alcohols to hydrogen bond amongst themselves explains their high melting points. For example, in ethanol, the negatively charged oxygen on one ethanol molecule is attracted to a positively charged hydrogen molecule on another ethanol molecule. The presence of a highly electronegative group allows alcohols to hydrogen bond with other molecules. From this information it becomes clear that the oxygen bears a significant partial negative charge, while the hydrogen bears a partial positive charge of the same magnitude. The oxygen in the covalent bond is highly electronegative thereby, pulling the majority of the electron density shared in the covalent bond towards itself. The bond existing between oxygen and hydrogen is significantly shorter than the bonds formed between carbon and hydrogen.
The following examples of primary, secondary, and tertiary alcohols are ethanol, isopropanol (IUPAC nomenclature: propan-2-ol), and tert-butyl alcohol (IUPAC nomenclature: 2-methylpropan-2-ol), respectively. By the same token, an alcohol is secondary if the carbon to which it is attached is bound to two other carbons, and tertiary if the carbon’s remaining three bonds are bonded to other carbons. An alcohol is primary if it is attached to a carbon with only one carbon-carbon bond. An alcohol is classified as a primary, secondary, or tertiary depending on the carbon it is attached to. Within the general functional group of alcohol, there are three subgroups: primary, secondary, and tertiary alcohols.
The chemical representation of a hydroxy group is –OH, indicating an oxygen atom covalently bonded to a hydrogen atom.
The presence of a hydroxy group indicates that the molecule is either an alcohol or a carboxylic acid. The hydroxy-group is one of many functional groups studied in organic chemistry. 7 Unique Infrared Spectroscopy of Alcohols and Phenols.3.3 Synthesis of Phenols: Nucleophilic Aromatic Substitution.
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