Question

Cetyl alcohol, \(\mathrm{C}_{16} \mathrm{H}_{33} \mathrm{OH}\), is a common ingredient of soaps and shampoos. It was once commonly obtained from whale oil, which is where it gets its name (cetyl is derived from cetacean). Draw the chemical structure for this compound.

Short answer

Draw a 16-carbon chain with \(\mathrm{OH}\) attached to the end.

Step-by-step solution

Identify the Components of the Molecule

Cetyl alcohol is represented by the molecular formula \(\mathrm{C}_{16}\mathrm{H}_{33}\mathrm{OH}\). This indicates it is made up of 16 carbon (C) atoms, 33 hydrogen (H) atoms, and one hydroxyl (OH) group.

Understand the Alcohol Group

The presence of \(\mathrm{OH}\) signifies that cetyl alcohol contains a hydroxyl group. In its structure, this group will often attach to the end carbon atom, as it is a primary alcohol.

Begin with the Hydrocarbon Chain

Start drawing the main portion of the structure, which is a carbon chain of 16 carbon atoms. Represent the chain as a zigzag line where each vertex denotes a carbon atom. Hence, there will be 16 carbons in a line.

Fill in the Hydrogen Atoms

Each carbon atom forms four bonds, counting bonds with hydrogen atoms. Given that it's a saturated molecule, each carbon in the middle of the chain will bond with two hydrogens, the terminal carbon will bond with three hydrogens, and the other terminal carbon which carries the \(\mathrm{OH}\) group will bond with two hydrogens.

Attach the Hydroxyl Group

Attach the \(\mathrm{OH}\) group to the terminal carbon atom. This hydroxyl group differentiates cetyl alcohol from simple hydrocarbons, creating an alcohol.

Review the Complete Structure

Ensure that the drawn structure contains all 16 carbon atoms and 34 hydrogen atoms in total (this includes the hydrogen in the \(\mathrm{OH}\) group, making 33 hydrogen as direct atoms and 1 from the hydroxyl group: 34 total), reaffirming it matches the formula \(\mathrm{C}_{16}\mathrm{H}_{33}\mathrm{OH}\).

Key concepts

Cetyl Alcohol

Cetyl alcohol is an interesting ingredient commonly found in many beauty and skincare products, such as soaps and shampoos. Its chemical formula is \( \mathrm{C}_{16} \mathrm{H}_{33} \mathrm{OH} \), which means it is a long-chain alcohol consisting of 16 carbon atoms, 33 hydrogen atoms, and one essential hydroxyl group. Originally, cetyl alcohol was derived from whale oil. This historical origin is reflected in its name, since 'cetyl' comes from 'cetacean,' the scientific order of aquatic mammals that includes whales. Nowadays, cetyl alcohol is usually produced through more sustainable means. It serves as an emollient, helping to make the skin feel smooth. Additionally, it acts as a thickening agent in products, giving them a rich, creamy texture.

Chemical Structure

The chemical structure of cetyl alcohol plays a crucial role in defining its properties. At a fundamental level, its structure consists of:

• A long chain of 16 carbon atoms.
• A hydroxyl group (\(\mathrm{OH}\)) attached to the terminal carbon atom.

The chain is usually drawn as a zigzag line, with each vertex representing a carbon atom. This configuration makes it a primary alcohol, due to the placement of the hydroxyl group at the end of the chain. Having a precise and accurate structure helps to understand how cetyl alcohol interacts with other ingredients in formulations, ensuring its effectiveness in cosmetics and personal care products.

Hydroxyl Group

The hydroxyl group is a critical functional group in the molecular structure of cetyl alcohol. It is represented by \( \mathrm{OH} \) and plays a pivotal role in defining the behavior and characteristics of this compound. The hydroxyl group makes cetyl alcohol a primary alcohol. It sits at one end of the carbon chain, attaching to the terminal carbon.

Properties of Hydroxyl Group

• Polar nature: The presence of \(\mathrm{OH}\) makes cetyl alcohol more polar than regular hydrocarbons, which affects its solubility and interactions.
• Hydrogen bonding: This property allows cetyl alcohol to form hydrogen bonds with water molecules or other compounds, affecting its use in product formulations.

This group is also responsible for the slightly higher melting point of cetyl alcohol compared to similar hydrocarbons without a hydroxyl group. Its presence is vital for cetyl alcohol's function as a versatile ingredient in both industrial and personal care applications.

Hydrocarbon Chain

A hydrocarbon chain is an integral part of cetyl alcohol's composition. The backbone of cetyl alcohol is made up of 16 carbon atoms with hydrogen atoms filling in the available bonding sites. This configuration classifies it as a saturated molecule, meaning there are no double or triple carbon bonds (all are single bonds). The length of the hydrocarbon chain influences the compound's characteristics, such as:

• Melting point: Longer chains tend to have higher melting points.
• Solubility: The length impacts its solubility in water and oils.
• Softness: The preference of longer chains for forming van der Waals forces makes them useful in creating creamy textures in products.

The zigzag arrangement of the carbon chain helps minimize steric hindrance, stabilizing the molecule overall. In cetyl alcohol, this long hydrocarbon chain's interaction with the hydroxyl group results in its unique properties, making it perfect for enhancing the quality of many personal care products.