Historically, alcohol has been used in association with social activities, including both religious and non-religious rituals, as a dietary component, and as a medicinal agent. Alcohol consumption by various cultures predates written history. Although it was once used for therapeutic purposes, it is no longer recommended as a therapeutic because of its ability to produce intoxication. The ability of ingested alcohol to get from the gut into the bloodstream and up to the brain where it produces the intoxicating effects is due to its chemical structure and solubility in water.
Chemical structure of alcohol
Alcohols are organic molecules assembled from carbon (C), oxygen (O), and hydrogen (H) atoms. When 2 carbons are present, the alcohol is called ethanol (also known as ethyl alcohol). Ethanol is the form of alcohol contained in beverages including beer, wine, and liquor.
Learn more about the formation of alcohol in beverages.
The chemical composition of ethanol can be represented either as a 1) molecular formula or as a 2) structural formula. The molecular formula of ethanol is C2H6O, indicating that ethanol contains two carbons and an oxygen. However, the structural formula of ethanol, C2H5OH, provides a little more detail, and indicates that there is an hydroxyl group (-OH) at the end of the 2-carbon chain (Figure 1.1). The -OH group is characteristic of all alcohols.
Figure 1.1 Two common ways to represent the structure of ethanol are shown. On the left is the atomic stick representation of the structural formula and on the right is the ball and stick model.
Ethanol is soluble in water
Ethanol is an interesting molecule. It is polar or hydrophilic (water-loving) due to the presence of the terminal hydroxyl group, so it dissolves in water. Yet because of the 2 carbon chain, it has a bit of non-polar character. There is no separation of electrical charges between the carbon atoms, thereby minimizing intermolecular interactions in aqueous solutions. Generally, carbon chains (saturated with hydrogens) give a molecule hydrophobic (water-fearing) character, making it less soluble in water. However, in the case of ethanol, the carbon chain is short enough so that the more polar -OH group dominates, giving the ethanol its polar character. In alcohols with relatively long carbon chains (4 or more), the polar effects of the -OH group are not sufficient to overcome the hydrophobic nature of the carbon chain, resulting in alcohols that are progressively less water-soluble.
The solubility characteristics of ethanol become important in terms of its ability to move across biological membranes and around the body. Because it is a small molecule (molecular weight = 46 g/mole), it fits through pores (holes) in the biological membrane. In fact, it distributes in any area within the body in which water is found. However, the 2-carbon chain in ethanol makes it slightly lipophilic (lipid-loving) so it can also penetrate the lipid bilayers of biological membranes.
Figure 1.2 The solubility of an alcohol depends on the presence of a terminal hydroxyl (OH) group, and the length of its carbon chain.