Question

Locate and identify the functional groups in (a) propylene glycol, one of the major ingredients used in electronic cigarettes; (b) glutaric acid, produced in the body during the metabolism of lysine and tryptophan; (c) lactic acid, from sour milk; and (d) phenylalanine, an amino acid found in proteins.

Short answer

(a) Propylene glycol: hydroxyl groups; (b) Glutaric acid: carboxylic acid groups; (c) Lactic acid: hydroxyl and carboxylic acid groups; (d) Phenylalanine: amine, carboxylic acid, and phenyl groups.

Step-by-step solution

Identify the Chemical Formula for Propylene Glycol

Propylene glycol has the chemical formula \( C_3H_8O_2 \). It is a diol, meaning it contains two alcohol groups.

Determine the Functional Groups in Propylene Glycol

In propylene glycol, the functional group present is the hydroxyl group \(-OH\), which is found in two locations. This characterizes it as an alcohol.

Identify the Chemical Formula for Glutaric Acid

Glutaric acid has the formula \( C_5H_8O_4 \). It is a dicarboxylic acid, meaning it has two carboxylic acid groups.

Determine the Functional Groups in Glutaric Acid

Glutaric acid contains two carboxylic acid functional groups \(-COOH\). It is a type of organic acid containing these moieties at both ends of a carbon chain.

Identify the Chemical Formula for Lactic Acid

The chemical formula for lactic acid is \( C_3H_6O_3 \). This compound can be classified as a hydroxy acid.

Determine the Functional Groups in Lactic Acid

Lactic acid contains a hydroxyl group \(-OH\) and a carboxylic acid group \(-COOH\), making it both an alcohol and a carboxylic acid.

Identify the Chemical Formula for Phenylalanine

Phenylalanine has the formula \( C_9H_{11}NO_2 \). It is an amino acid, which typically contains an amine group and a carboxylic acid group.

Determine the Functional Groups in Phenylalanine

In phenylalanine, the functional groups include an amine group \(-NH_2\) and a carboxylic acid group \(-COOH\). Additionally, it has a phenyl group (a benzene ring attached to the carbon chain), which characterizes it as an aromatic amino acid.

Key concepts

Propylene Glycol

Propylene glycol is an organic compound with the chemical formula \( C_3H_8O_2 \). It is widely used in various industries, including the food, pharmaceutical, and cosmetic industries, and is also a major component in electronic cigarettes.
The defining feature of propylene glycol is its functional group: the hydroxyl group. This compound belongs to the class of diols, which are alcohols containing two hydroxyl \(-OH\) groups.

• The presence of these hydroxyl groups makes propylene glycol very effective in attracting and retaining water, contributing to its moisturizing properties in skin-care products.


• These \(-OH\) groups also play a role in its solvent capabilities, making it an excellent carrier for flavors and other ingredients.

This melting point and other chemical characteristics of propylene glycol are largely influenced by these functional groups, making it versatile in applications from antifreeze agents to de-icing solutions.

Glutaric Acid

Glutaric acid, with the chemical formula \( C_5H_8O_4 \), is a unique organic compound found naturally in the body during the metabolism of certain amino acids such as lysine and tryptophan.
It falls under the category of dicarboxylic acids, which are characterized by having two carboxylic acid functional groups \(-COOH\).

• These functional groups grant glutaric acid acidic properties that are essential during chemical reactions within the body.


• The presence of two carboxylic groups enables it to participate in reactions that require a strong acidic compound, impacting energy metabolism and synthesis of other important biomolecules.

Because of these properties, glutaric acid also finds use in various medical and industrial applications, including the manufacturing of polymers and as a buffering agent in various formulations.

Lactic Acid

Lactic acid is a well-known compound with the chemical formula \( C_3H_6O_3 \), often associated with muscle soreness after intense exercise. It is formed during the anaerobic respiration of glucose and is prevalent in sour milk and yogurt.
Lactic acid is classified as a hydroxy acid due to its structure containing both a hydroxyl group \(-OH\) and a carboxylic acid group \(-COOH\).

• The dual presence of these functional groups gives lactic acid its characteristic acidic properties while also enabling its ability to engage in hydrogen bonding, increasing solubility in water.


• This solubility makes it useful in food preservation and flavoring, as well as in skincare products for its mild exfoliating properties.

Consequently, lactic acid is a vital component both in the food industry and in cosmetic formulations, valued for its gentle yet effective properties.

Phenylalanine

Phenylalanine is an essential amino acid with the molecular formula \( C_9H_{11}NO_2 \). Found in many protein-rich foods, it plays a critical role in human health.
As an amino acid, phenylalanine contains both an amine group \(-NH_2\) and a carboxylic acid group \(-COOH\). Additionally, it features a phenyl group, which is a benzene ring attached to the carbon chain, making it aromatic.

• The combination of these functional groups is responsible for phenylalanine's role as a precursor to dopamine, norepinephrine, and other signaling molecules in the brain.


• Its aromatic nature also contributes to its ability to participate in protein structure by contributing to hydrophobic interactions, which help stabilize protein formation.

Understanding phenylalanine’s structure and its functional groups is crucial for appreciating its essential functions in nutrition and neurochemistry.