Question

Consider a compound called hexanol. Chemists can tell from its name that it has six carbons (hex-) and it is an alcohol (-ol). a. What is the molecular formula of hexanol? b. Draw a possible structural formula for hexanol. c. Is the molecular formula or the structural formula more useful in determining the smell of hexanol? Explain.

Short answer

a. The molecular formula is \( C_6H_{14}O \). b. The structural formula involves a chain of six carbons with an -OH group. c. The structural formula is more useful for determining smell.

Step-by-step solution

Determining the Molecular Formula

Hexanol is an alcohol with six carbon atoms. For alcohols, the general formula is \( C_nH_{2n+1}OH \). Here, \( n = 6 \) for hexanol. Substitute \( n \) into the formula to get \( C_6H_{2(6)+1}OH \), which simplifies to \( C_6H_{13}OH \). Thus, the molecular formula is \( C_6H_{14}O \).

Drawing the Structural Formula

A structural formula for hexanol needs to show the arrangement of all atoms within the molecule, specifically showing the -OH group attached to one of the carbon atoms. Start by drawing a chain of six carbon atoms. Attach hydrogen atoms to each carbon atom so that each carbon forms four bonds. Lastly, attach an -OH group to the terminal carbon atom to indicate the alcohol functional group.

Comparing Molecular and Structural Formulas

The molecular formula \( C_6H_{14}O \) provides the number and type of atoms but no information about their arrangement, which is crucial in determining properties like smell. The structural formula shows the arrangement of atoms, influences molecular shape, and affects interactive capabilities and properties like smell. Therefore, the structural formula is more useful in determining the smell of hexanol.

Key concepts

Molecular Formula

A molecular formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. For organic compounds like hexanol, the molecular formula tells us the number and types of atoms involved. Hexanol's molecular formula is calculated using the general formula for alcohols, which is \( C_nH_{2n+1}OH \). By substituting \( n = 6 \) (since hexanol has six carbon atoms), we arrive at the formula \( C_6H_{14}O \). This indicates the presence of six carbon atoms, fourteen hydrogen atoms, and one oxygen atom. This kind of formula is quite useful for ensuring that the basic chemical composition of a compound is understood at a glance.
However, it doesn't convey the arrangement of atoms, which can have significant implications for the compound's characteristics. Thus, while it provides an essential snapshot of the chemical makeup, it is limited when it comes to understanding the compound's detailed properties.

Alcohols

Alcohols are a group of organic compounds where the defining feature is the presence of an -OH (hydroxyl) group. This group categorizes a compound as an alcohol and confers specific properties to it. Hexanol, for example, is an alcohol with six carbon atoms. The presence of the hydroxyl group in alcohols significantly impacts their chemical behavior, such as their solubility in water and ability to form hydrogen bonds.
In naming alcohols, the suffix "-ol" is used to indicate the hydroxyl group. For hexanol, it tells us that regardless of other structural variations, the key functional characteristic is the presence of an alcohol group. This functional group takes precedence in determining the chemical and physical properties of the molecule.

• Alcohols are generally more soluble in water than other organic compounds due to hydrogen bonding.
• Their boiling points are typically higher than those of hydrocarbons of similar molecular weight.

Understanding the basic nature of alcohols helps chemists predict how compounds like hexanol will behave in different environments.

Structural Formula

The structural formula of a compound provides a visual map of how atoms are arranged within a molecule. In contrast to the molecular formula, which acts merely as a headcount of atoms, the structural formula illustrates connections and placement. For hexanol, this means laying out how the six carbon atoms are arranged in a chain, how they are bonded with hydrogen atoms, and critically, where the -OH group is positioned.
To draw the structural formula for hexanol, you begin by constructing a straight chain of six carbon atoms. Each carbon must satisfy its four-bond requirement, which generally results in a straightforward zigzag line of bonds in linear representations. The -OH group must be attached to one end of this chain or potentially along its length in different isomeric forms. This helps in predicting the chemical perceptions like taste or smell, as molecular shape and atom arrangement can dramatically change a substance's characteristics.

Functional Groups

Functional groups are specific groupings of atoms within molecules that have their own characteristic properties and reactivities. The -OH group in alcohols is a prime example of a functional group. In hexanol, this hydroxyl group defines the compound's identity as an alcohol. Functional groups are the true cornerstones of chemistry as they set the stage for a molecule's functional behavior in reactions.
The presence of specific functional groups can greatly alter the net characteristics of an organic compound:

• They determine the kinds of reactions the compound will undergo.
• They influence physical properties like boiling point and solubility.
• They significantly impact the sensory properties of a compound, such as smell and taste, crucial for applications in perfumes and flavors.

In the case of hexanol, the alcohol functional group is what makes it soluble in water compared to many other hydrocarbons and why it could potentially be used to create fragrances or other products where smell is an important factor.