Chembloggers: Aldehydes

Although you might think of hides when you first hear the word 'aldehyde', You're way off.

Aldehydes are a class of organic molecules. They are very useful (not as furry rugs on the floor or coats).Two of the most important aldehydes are formaldehyde and acetaldehyde. They are used in the sysnthesis of other chemicals, disinfectants and preservers.

Aldehydes mostly release pleasant odours. They are essentially alcohols that have lost the Hydrogen atom.

This is their general formula.

In this diagram, the 'R' represents a Carbon chain. It can be very long or non-existant(methanal). The Carbon atom double bonded to the Oxygen is called a carbonyl group. Aldehydes always have a Hydrogen atom attatched to their structure (whereas ketones have Carbon chains on both sides)

Rules for naming Aldehydes:

1) Identify the parent chain (it must have the Carbonyl group at the end).

2) Count the number of Carbon atoms on the longest chain.

3) Assign each Carbon a number- the Carbonyl group counts as '1'.

4) Name the molecule as if the Carbonyl group wasn't there (ethane, propane, butane, etc)

5) Remove the 'e' from the end of the name and add the suffix 'al'.

Note: Similarly to naming alcohols, if there are multiple Carbonyl groups, add prefixes(di, tri, tetra, penta, etc.) before the 'AL' but after the alkane name.

Can you see how similar aldehydes and alcohols are? They are like sisters; relatively similare in structure, but with very different personalities! Ariel's sisters are very dutiful and obey their father. Meanwhile, Ariel is off going up to shore where she is forbidden!

Now for some practise.

First, figure out what type of molecule this is. Since there is a Carbonyl group at the end, we can conclude that it is a aldehyde. Next, count the number of Carbons on the longest chain. Name the molecule as if there was no Carbonyl group. So, butane. Then add take off the ending 'e' (we can leave 'an' because there are no double bonded Carbons) and add 'AL'. So the final name for our molecule is butanal!

Let's try another, this time we have to name the molecule.

4-ethyloctanal

First draw the parent chain:

Because the ending is octanal, take off the 'AL' and add 'ane'. Thus, octene. Draw the chain.

Next, make the molecule an aldehyde. Add the double bonded Oxygen at the end of the structure. Assign the number '1' to the Carbon and number the remaining Carbons.