Difference Between Aldehydes and Ketones

Aldehydes vs Ketones

Aldehydes and ketones are two different kinds of organic compounds. Both can be made artificially although there are many natural sources of such. The confusion between the two may have rooted in their chemical structures. Although the two have an oxygen atom that is double bound to a carbon atom (C=O), the difference in the remaining atomic arrangement and also on the other atoms bounded to the carbon (in the C=O) spell the main and only primary dissimilarity between them. By the way, the C=O is technically referred to as a carbonyl group.

In aldehydes, the (C=O) is found at the carbon chain’s end. This means that the (C) carbon atom will be bounded to a hydrogen atom plus another carbon atom. With ketones, the (C=O) group is usually found at the center of the chain. Thus, the carbon atom in the C=O will be linked to two separate carbon atoms at each side.

This carbonyl group arrangement of the aldehydes makes it a better compound for oxidization into carboxylic acids. For ketones, it is a tougher feat to do because you first have to break one of the carbon to carbon (C-C) bond. This characteristic tells one of the most important functional differences between the two.

Moreover, the two compounds show lots of distinct effects when mixed with certain reagents. This process is the basis for many chemical tests that help spot the type of chemical under study. Thus, in distinguishing the two these tests often show varied results:

o For the Schiff’s test, aldehydes show a pink color while ketones don’t have any color at all.

o In Fehling’s test, there’s an occurrence of a reddish precipitate while in ketones there’s none.

o For Tollen’s test, a black precipitate is formed while in ketones there’s again none.

o With the sodium hydroxide test, aldehydes show a brownish resinous material (except for formaldehyde) while ketones don’t have any reaction to such.

o For the reagent sodium nitroprusside plus some drops of sodium hydroxide, aldehydes emit a deep reddish color while ketones exhibit a reddish color which later transforms to orange.

An example of an aldehyde is cinnamaldehyde while the simplest form of ketone is probably acetone.

1. In aldehydes, the carbon atom in the carbonyl group is bounded to a hydrogen and one carbon atom while in ketones it is bound to two other carbon atoms.
2. Aldehydes have carbonyl groups found at the end of the carbon chain while ketones have carbonyl groups usually positioned at the center of the chain.
3. Aldehydes and ketones display varying results when combined with chemical reagents. For the majority of such, ketones usually don’t give any reaction compared to aldehydes.

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