Question

Name all the aldehydes and ketones that have the formula \(\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O} .\)

Short answer

The aldehydes and ketones that have the formula \(\mathrm{C}_{5}\mathrm{H}_{10}\mathrm{O}\) are: 1. Pentanal 2. 2-Pentanone 3. 3-Pentanone

Step-by-step solution

Drawing possible structures for aldehydes

Since the carbonyl group in aldehydes is always at the end of the carbon chain, there is only one possible structure: a straight chain with five carbon atoms, and the carbonyl group at one end.

Naming the aldehyde

According to IUPAC nomenclature, we should name this compound by identifying the longest carbon chain containing the carbonyl group (which is 5 carbons long) and adding the suffix -al to the parent name. Since the longest chain has five carbon atoms, the parent name is pentane. Therefore, the name of this aldehyde is pentanal.

Drawing possible structures for ketones

In ketones, the carbonyl group is located in the middle of the carbon chain. Since there are five carbons in the chain, there are two possible positions for the carbonyl group: on the second carbon (counting from one end) or on the third carbon (counting from the other end). To avoid duplicates, since the molecule can be flipped, there are two unique structures.

Naming the ketones

To name these ketones according to the IUPAC nomenclature, we should find the longest carbon chain containing the carbonyl group (which is 5 carbons long in both cases). Then, we will add the suffix -one to the parent name. For the first structure, the carbonyl group is on the second carbon atom of the chain. So, the parent name is pentane, and we will add the prefix "2-" to indicate the location of the carbonyl group. The name of this ketone is 2-pentanone. For the second structure, the carbonyl group is on the third carbon atom of the chain. The parent name is also pentane, and we need to include the prefix "3-" to indicate the position of the carbonyl group. The name of this ketone is 3-pentanone. The aldehydes and ketones with the given molecular formula are: 1. Pentanal 2. 2-Pentanone 3. 3-Pentanone

Key concepts

IUPAC nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) devised a standard naming system for organic compounds. This is to ensure consistency and clarity across various scientific disciplines. The IUPAC nomenclature helps in identifying the composition and structure of a molecule from its name. For instance, in aldehydes and ketones, the naming involves identifying the longest carbon chain that contains the carbonyl group. Determining the correct names involve recognizing the functional groups and their position along the chain.
- Aldehydes are named by changing the suffix of the parent alkane's name from "-e" to "-al." If the aldehyde is based on a 5-carbon chain, as in our example, it is called pentanal. - For ketones, the suffix is changed from "-e" to "-one." Additionally, the position of the carbonyl group is indicated by a number. Thus, a 5-carbon chain with a carbonyl group at the second position is named 2-pentanone, and at the third position, it is 3-pentanone.
Using this systematic approach, scientists and students can accurately depict multiple isomers and explore more complex molecular variations.

carbonyl group

The carbonyl group is a key functional group in organic chemistry characterized by a carbon atom double-bonded to an oxygen atom \((C=O)\). This group is pivotal in defining the properties of aldehydes and ketones.
- Aldehydes contain a carbonyl group at the end of the carbon chain. This placement results in a distinct set of properties, such as lower boiling points relative to alcohols, because aldehydes cannot form hydrogen bonds among themselves.- Ketones, on the other hand, have the carbonyl group situated in the inner part of the carbon chain. This internal position contributes to ketones having varying degrees of reactivity and different physical properties compared to aldehydes.
The carbonyl group is polar, opening avenues for interactions with other molecules. Its presence in the middle of a carbon chain in ketones affects the molecule's symmetry and how it can interact in chemical reactions, like nucleophilic additions.

structures of organic compounds

Organic compounds are composed of carbon-based molecules that exhibit diverse structures. The backbone of these structures is often defined by carbon chains of varying lengths and configurations. Aldehydes and ketones are two types of organic compounds defined by the presence and position of the carbonyl group.
- In aldehydes, the carbon chain ends with a carbonyl group. Therefore, when drawing structures involving simpler aldehydes like with five carbons, there is essentially one way to arrange them, resulting in only one structure to consider. - Ketones, however, allow for more structural diversity due to the flexibility of the carbonyl position. As seen in the textbook exercise, a 5-carbon ketone can have its carbonyl group on the second or third carbon atom. This ability to vary leads to different isomers being possible even with the same molecular formula.
Understanding the structures of aldehydes and ketones is essential for predicting both physical and chemical properties. It also plays a crucial role in the synthesis and application of these compounds in various industrial and biological processes.