Question

Name the following compounds. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHO}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\) (d) \(\mathrm{H}_{2} \mathrm{CO}\) (e) \(\mathrm{CH}_{3} \mathrm{CHO}\)

Short answer

The names of the compounds are: (a) Butanal, (b) Butan-2-one, (c) Propanone, (d) Methanal, (e) Ethanal.

Step-by-step solution

Identify the functional groups

Identify the functional group in each compound. It will help you determine the suffix of the compound name. For example, if the functional group is an aldehyde, the suffix is '-al'. If it is a ketone, the suffix is '-one'.

Identify the longest carbon chain

Find the longest chain of carbon atoms in the compound. This will serve as the base of your compound name, known as the root or parent name. The length of the chain determines the first part of the compound name. For example, if the chain has 3 carbon atoms, the first part is 'propane'.

Identify the position of the functional groups

Identify the position of the functional group. The number represents the carbon atom in the chain on which the functional group is located. Numbering should be done in such a way that the functional group gets the lowest possible number. Add these numbers to the beginning of the compound name.

Naming the compounds

(a) The compound \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHO}\) is identified as an Aldehyde (CHO group) on a 4-carbon chain (butane). The aldehyde is on the first carbon, hence it is Butanal. (b) The compound \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) is identified as Ketone (CO group) on a 4-carbon chain (butane). The ketone is on the second carbon, hence it is Butan-2-one. (c) The compound \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\) is identified as Ketone (CO group) attached to two methyl groups. Hence it is Propanone. (d) The compound \(\mathrm{H}_{2} \mathrm{CO}\) is identified as Aldehyde (CHO group) attached to one hydrogen. Hence it is Methanal. (e) The compound \(\mathrm{CH}_{3} \mathrm{CHO}\) is identified as Aldehyde (CHO group) attached to one methyl group, therefore it is Ethanal.

Key concepts

Functional Groups

Understanding functional groups is vital to mastering the art of organic chemistry. Functional groups are specific groups of atoms within molecules that determine the characteristic reactions of those molecules. Think of them as the active parts of molecules that give organic compounds their unique properties. They are the key players in the structure and reactivity of organic molecules and form the basis for naming organic compounds.

Some common functional groups are hydroxyl (-OH), carboxyl (-COOH), amine (-NH2), and the ones relevant to our exercise, aldehydes (-CHO) and ketones (C=O). Recognizing the functional group present in a molecule helps us predict its chemical behavior and how it might interact with other molecules.

Aldehydes and Ketones

Aldehydes and ketones are two closely related functional groups that feature prominently in the naming of organic compounds. Aldehydes have a carbonyl group (a carbon double-bonded to oxygen) at the end of a carbon chain, while ketones have their carbonyl group in the middle of the chain. This seemingly small difference has a significant impact on chemical reactivity and nomenclature.

For aldehydes, the carbonyl group will always be at the end of the carbon chain, resulting in a suffix '-al' in IUPAC nomenclature. For example, ethanal and butanal from our exercise. Ketones, on the other hand, have their carbonyl group bonded to two other carbons and have a suffix '-one'. Positioning is important for ketones, as demonstrated with butan-2-one in our problem set, where the number indicates the position of the carbonyl group.

IUPAC Nomenclature

The IUPAC nomenclature system is a set of internationally accepted rules for naming chemical compounds. It provides a way to give each compound a unique and unambiguous name. This system involves several steps, starting with identifying the longest carbon chain to give the parent name, determining the primary functional group for the suffix, and numbering the chain to reflect the position of the functional group and any substituents.

Using this systematic approach ensures clear communication among chemists across the world. In the given exercise, the student is tasked with implementing this nomenclature system to accurately name compounds with aldehydes and ketones. For instance, a four-carbon aldehyde must be named butanal, not just any four-letter prefix with '-al' tacked on the end.

Carbon Chain Identification

Identifying the longest carbon chain in an organic compound is a fundamental step in naming it according to IUPAC guidelines. The longest chain serves as the 'backbone' of the molecule and determines the root name. Different lengths of carbon chains have predefined names, like eth- for two carbons, prop- for three, but- for four, and so forth.

Once the root is determined, the next step is locating the functional group and numbering the carbons in the chain such that the functional group has the lowest possible number. For complex molecules, additional rules cover how to name substituents and branches. Accurate identification of the carbon chain is crucial as it is the foundation upon which the correct name of the compound is built, thereby affecting both the compound's classification and the understanding of its properties and potential reactions.