Naming Aldehydes - Online Tutor, Practice Problems & Exam Prep

Aldehydes are organic compounds characterized by a carbonyl group bonded to at least one hydrogen atom. When naming aldehydes, the carbon of the carbonyl group is assigned the number one position in the carbon chain, indicating its priority in the structure. The suffix "-al" replaces the "-e" in the corresponding alkane name to signify the presence of the aldehyde functional group. Substituents are located numerically, ensuring accurate representation of the molecule's structure. This systematic approach to nomenclature allows for the clear identification and classification of aldehydes within organic chemistry.

Rules for Naming Aldehydes

Now recall that aldehydes possess a carbonyl carbon connected to an H atom. Now, the set of rules for naming aldehydes are similar to ketones. The exception here, though, is that the carbonyl carbon of the aldehyde is always numbered 1. So that's where we're going to start numbering our longest carbon chain at the carbonyl carbon of the aldehyde.

Here, because we have an aldehyde, a new functional group, we're going to have to modify our ending here. We're going to modify the E ending of the original alkane name to Al because it's an aldehyde. In terms of our naming convention, we'd still have to give the locations of our substituents the numerical locations we'd have to give the parent name with its modified ending, or we're changing E to al.

So keep this in mind as we investigate all these different types of aldehydes.

Naming Aldehydes Example

Provide a systematic name for the following aldehyde. Now in order to do this, we're going to utilize the following steps. Step one find the longest carbon chain which will represent the parent chain and a sign name according to the prefixes and modifier. The pair change should include the aldehyde group and greater number of carbons. If a tie between longest chains choose chain with more substituents.

So here if we take a look, we need to include our carbonyl carbon as part of the longest carbon chain. And remember in terms of numbering we start numbering from that carbon. Our longest carbon chain would be here. If we look, this is not part of the longest carbon chain because this is our branch group, our alkyl group. It's made-up of two carbon, so this would be ethyl. So we've assigned name to all the substituents.

Step three, start numbering the chain at the carbon of the aldehyde group. So this would be 1, 2, 3, 4, 5 and 6 steps, four to six. Repeat steps from previous naming topics. If you haven't watched my video on alkane with substituents, I suggest that you go back and take a look because there we talk about steps 4 to 6 where we're basically paying attention to these substituents. We have to give the numerical locations of our substituents and make sure we need them alphabetically.

Also gives us. How do we set up the name when we're using commas to separate numbers from each other and dashes to separate numbers from letters? So here we have an ethyl on carbon 2, so it would be 2-ethyl. Because the aldehyde carbon is always going to be carbon number one, we don't need to designate where it's located. O Here we have a six carbon chain which an alkane form is hexane. But remember we're changing the E to L so it becomes hexanal. So the name of this particular aldehyde would be 2-ethylhexanal.

Provide the systematic name for the following aldehyde.

• A. 4-fluoro-5-methylheptanal
• B. 4-fluoro-5-ethylhexanal
• C. 4-fluoro-5-methylheptanone
• D. 4-fluoro-5-ethylhexanone

Which of the following compounds represent 2-bromo-pentanal?

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the common name of the simplest aldehyde?

The simplest aldehyde is commonly known as formaldehyde. Its chemical formula is CH₂O, and it consists of a single carbon atom bonded to two hydrogen atoms and one oxygen atom. The oxygen atom is double-bonded to the carbon, which is a characteristic feature of aldehydes. Formaldehyde is a colorless gas at room temperature with a pungent, distinct odor and is widely used in various industries, including the manufacture of building materials, as a preservative in medical laboratories and as a disinfectant. It's important to handle formaldehyde with care, as it is toxic and can be harmful to health with prolonged exposure.

What is the IUPAC name of aldehyde?

The term "aldehyde" is a functional group in organic chemistry rather than a specific compound, so there isn't a single IUPAC name for "aldehyde." Instead, aldehydes are named according to the IUPAC nomenclature system based on the longest carbon chain they are attached to and the fact that they contain the carbonyl group (C=O) at the end of that chain.

The IUPAC name for an aldehyde is derived by taking the name of the corresponding alkane chain, dropping the 'e' at the end, and adding the suffix '-al'. For example, the simplest aldehyde, with just one carbon atom and a hydrogen atom attached to the carbonyl group, is called methanal. Its common name is formaldehyde. Another example is ethanal, commonly known as acetaldehyde, which has two carbon atoms with the carbonyl group attached to the terminal carbon.

Remember, for aldehydes with longer carbon chains or additional functional groups, the naming becomes more complex, and you may need to indicate the position of the aldehyde group and other substituents using locants (numbers) in the name.

How do you name an aldehyde?

Naming an aldehyde in organic chemistry follows the International Union of Pure and Applied Chemistry (IUPAC) nomenclature system. Here's a step-by-step guide to naming an aldehyde:

1. Identify the longest carbon chain that contains the aldehyde group (the carbonyl group with at least one hydrogen atom attached, -CHO).
2. The longest chain becomes the base name and is named according to the number of carbons it contains, using the appropriate alkane name (e.g. methane, ethane, propane, etc.).
3. Replace the "-e" ending of the alkane with "-al" to indicate the presence of an aldehyde group. For example, ethane becomes ethanal.
4. Number the carbon chain starting from the end nearest to the aldehyde group. Since the aldehyde carbon is always at the end of the chain, it is automatically assigned the number 1.
5. If there are any other substituents (like methyl, ethyl groups, or halogens) on the carbon chain, indicate their position by numbers and their names in alphabetical order before the base name.
6. If the aldehyde is attached to a ring, the suffix "-carbaldehyde" is used, and the ring is named first.

For example, a four-carbon chain with an aldehyde group would be named butanal.

How do you name an aldehyde as a substituent?

When an aldehyde group is a substituent on a larger molecule, it is named as a "formyl" group. To name an aldehyde as a substituent, you follow these steps:

1. Identify the longest carbon chain that will serve as the parent compound. If the aldehyde is not the highest priority functional group, then you will treat it as a substituent.
2. Number the carbon atoms in the parent chain starting from the end nearest to the formyl group to ensure it receives the lowest possible number.
3. The formyl group is indicated by the prefix "formyl-" followed by the position number it occupies on the carbon chain. If the formyl group is attached to a ring, the prefix "formyl-" is used without a number, as the position is implied to be at the point of attachment.
4. Combine the position number (if applicable), the prefix "formyl-", and the name of the parent chain into one word.

For example, if a formyl group is attached to the third carbon of a pentane chain, the compound would be named as 3-formylpentane. If it's attached to a benzene ring, it would simply be formylbenzene.