Question

Name the following compounds: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\); (b) \(\mathrm{CH}_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\); (c) \(\mathrm{CH}_{3} \mathrm{CCCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\); (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) -

Short answer

(a) Propanal, (b) 1-Butanol, (c) 3-Chlorohexane, (d) 3-Hexanone.

Step-by-step solution

Identify Functional Groups

Determine the functional groups present in each compound to guide the nomenclature process. (a) Aldehyde group. (b) Alcohol group. (c) Chlorine substituent on an alkane chain. (d) Ketone group.

Determine Longest Carbon Chain

Find the longest continuous carbon chain that includes the functional group, which becomes the parent chain. (a) 3 carbons - Propane. (b) 4 carbons - Butane. (c) 6 carbons - Hexane. (d) 6 carbons - Hexane.

Assign Locants to Functional Groups and Substituents

Number the carbon atoms in the parent chain beginning with the end nearest the functional group or substituent to assign the lowest possible numbers. (a) Aldehyde at C1. (b) Alcohol at C1. (c) Chlorine at C3. (d) Ketone at C3.

Name by IUPAC Rules

Combine the parent chain name, locants, and names of functional groups or substituents to create the IUPAC name. (a) Propanal (no need for a number since aldehydes are always on the end). (b) 1-Butanol. (c) 3-Chlorohexane. (d) 3-Hexanone.

Key concepts

Functional Groups

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. When it comes to naming organic compounds, identifying these functional groups is crucial. For example, an aldehyde group, which contains a carbonyl group (a carbon double-bonded to an oxygen) at the end of a carbon chain, significantly affects the properties of the compound and is denoted by the suffix '-al' in IUPAC nomenclature.

Other common functional groups include alcohols, which have a hydroxyl group (-OH) and are indicated by the suffix '-ol', and ketones, which have a carbonyl group located within the carbon chain, denoted by '-one'. Understanding functional groups allows us to predict the compound's reactivity and physical properties, which is essential for chemists in various fields such as pharmaceuticals and materials science.

Carbon Chain Identification

The backbone of an organic molecule is the carbon chain, which provides the structure upon which functional groups are attached. Identifying the longest continuous carbon chain in a molecule is a primary step in the IUPAC naming process. This longest chain is often referred to as the 'parent chain' and it dictates the base name of the compound.

The length of the carbon chain is indicated by a root word (e.g., 'meth' for one carbon, 'eth' for two carbons, and so on). Even if there are multiple possibilities for the longest chain, the correct choice includes the highest number of functional groups, aligning with the principle of prioritizing functional groups in nomenclature. Once the parent chain is established, additional branches or substituents are identified and named accordingly.

Organic Compound Naming

Naming an organic compound according to IUPAC standards involves combining various elements including the parent chain, functional groups, substituents, and their positions. The complete name is formed by prefacing the base name of the longest chain with the names of any substituents, and their locants, then following it with the name of the functional group which also sometimes contains its locant. However, there are ordering rules to be followed; substituents are listed in alphabetical order.

The exercise examples provided illustrate these principles. The compound with the aldehyde group is named 'propanal'; there is no numerical locant for the aldehyde because it is understood to be at the end of the chain. In the ketone example, the compound is named 'hexanone' with a prefix '3-' to indicate the position of the ketone group on the carbon chain.

Locant Assignment

The locant is the number assigned to the carbon atoms in the chain to indicate the position of the functional groups or substituents. When providing a locant for these groups, the numbering must start from the end of the carbon chain closest to the first point of difference, ensuring that the groups receive the lowest possible numbers.

For alcohols and compounds with substituents, such as the provided examples of 1-butanol and 3-chlorohexane, the locant before the name specifies the carbon to which the functional group or substituent is attached. If there is no possibility of ambiguity, such as with terminal aldehyde groups, the locant may be omitted. Mastering locant assignment is crucial for professionals in organic chemistry and related disciplines, as it avoids confusion and ensures clear communication about molecular structure.