What are Carbonyl Compounds?

The compounds comprising of a carbonyl group -C=O are termed as Carbonyl Compounds. These compounds are a part of the organic chemistry with their primary members named as aldehydes and ketones.

Carbonyl Group

A carbonyl group is also called a functional group. It consists of a carbon atom which is linked to the oxygen atom through a double bond as shown below. This group is called the carbonyl group. The term Carbonyl also refers to carbon monoxide as the ligand within an organometallic or inorganic compound say a metal carbonyl for ex- nickel carbonyl.

Carbonyl Compounds

Again carbonyl compounds are divided into organic and inorganic carbonyl compounds, but in this article, we are dealing with the carbonyl compounds those of organic in nature.

Organic Carbonyl compounds

These include carbamates, urea and also the derivatives of phosgene, acyl chlorides chloroformates, carbonate esters, lactones, thioesters, lactams, isocyanates, and hydroxamates.

Carbonyl Compounds – Aldehydes and Ketones

In general, we come across the names aldehydes and ketones when we speak about the Carbonyl compounds. What is the role of these in the lists of carbonyl compounds? Aldehydes and ketones are the organic compounds which consist of the functional group as that of the carbonyl compounds. The main difference between these two compounds is the position of the carbonyl group. In aldehydes, the carbonyl group is placed at the ending of the carbon chain whereas, in the ketones, it is located in the middle of the carbon ring. The examples of aldehydes include propanol, butanol, 4-chlorobutanol, etc. and some of the examples of ketones are propanone, acetone, 2-methyl-3-pentanone, etc.

Properties of Carbonyl Compounds

Some of the properties of carbonyl compounds are given below:

  • These are to be polar in nature. They exhibit both positive as well as negative charge in slight form. Hence these are said to be polar molecules.
  • These compounds are reported to be insoluble in water but sometimes they dissolve other forms of polar molecules.
  • These are known to be as chemically reactive compounds. It means that they control the reactions of a chemical reaction.

Carbonyl Compounds Reactions

The carbon atom of the carbonyl group is said to be electrophilic in nature as they tend to attract electron-rich compounds. Some of the Examples of electrophiles include ions whereas the oxygen atoms are said to be nucleophiles as they do not have the rich density of electrons. They are said to be the lovers of nuclei such as the bases. The carbonyl compounds reactions are given below:

  1. Carbonyl Reduction: This reaction is a process in which the Carbonyl groups are reduced by the hydride reagents such as the LiAlH4 and NaBH4 with baker’s yeast, or by the process of catalytic hydrogenation.
  2. Carbonyl alkylation: This is a process in which the carbonyl compounds are alkylated with the use of organometallic compounds like Grignard reagents, organolithium reagents, acetylides, etc.
  3. Carbonyl Alpha-Substitution Reaction: This kind of substitution reaction involves the substitution of the atom of α hydrogen by an electrophile.

Applications of Carbonyl Compounds

  • The carbonyl compound propanone is used as a solvent since it gets dissolved in water as well as other organic solutions.
  • Formaldehyde is used in the manufacture of plastics and also it is used in the biological laboratories for preservation purposes.
  • Butanol is used to provide fragrance for keeping the bread fresh.
  • Acetaldehyde is used as a Synthesizer in many organic reactions.

Aldehydes and Ketones

These classes of organic compounds contain a carbonyl functional group (C=O) with structures CHO for aldehydes and RC(=O)R’ for ketones. Here, R and R’ denotes substituents of carbon. They also refer to as the methanoyl group or formyl group.  Aryl or alkyl group or its substituents fill in the remaining bonds of carbon atom in this group.

However, if the substituents in neither of the 2 remaining bonds are hydrogen, then the organic compound is a ketone. However, if one of the substituents is hydrogen then the organic compound is an aldehyde. The properties of aldehydes and ketones play a very important role in the uses of aldehydes and ketones.

Uses of Aldehydes and ketones

Aldehydes and ketones find application in different sectors such as pharmaceutical, food, fragrance, cosmetics because of their chemical properties. Refer below to learn more about the various applications and uses of aldehydes and ketones.

Uses of Aldehydes

  • Formaldehyde is found in the gaseous form. However, formaldehyde with a 40% solution in water forms formalin. Formalin helps in the preservation of biological specimens.
  • Formaldehyde reacting with phenol forms a compound Bakelite. Bakelite finds its application in plastics, coatings, and adhesives.
  • The compound- formaldehyde is essential during many industrial processes such as embalming, glue preparation, tanning and manufacture of polymeric products.
  • It acts as germicide, insecticide, and fungicides.
  • Formaldehyde helps in the testing of drugs. It is also used in photography.
  • Production of acetic acid and pyridine derivatives is possible from the compound “acetaldehyde.”
  • Benzaldehyde (aldehyde) is an essential component for the production of perfumes, cosmetic products, and dyes. It is added to incorporate almond flavour into various food products. It also acts as a bee repellant.

Uses of Ketones

  • Ketone behaves as an excellent solvent for certain types of plastics and synthetic fibres.
  • Acetone act as a paint thinner and a nail paint remover.
  • It also is used for medicinal purposes such as chemical peeling procedure as well as acne treatments.
  • Butanone, also known as methyl ethyl ketone, is one of the common solvents. It is used in textile production, varnishes production, paint remover production, paraffin wax production, plastic production, etc.
  • Another important ketone is cyclohexanone which is an important component in nylon production.

Aldehydes and Ketones in Perfumes

Aldehydes and ketones impart some very characteristics of fragrance in compounds. For instance, ketones help in the formation of a compound “acetophenone” which is responsible for fragrances such as cherry, jasmine, honeysuckle, almond, strawberry, etc. However, aldehydes are a well-known source of perfumes and fragrances in comparison to ketones.

Aldehydes in Baked Goods and Herbs

Everyone loves the scent of freshly baked cookies. But do you know the delicious scents of cookies baking in an oven are due to aldehydes? Aldehydes are an essential component in particular sugars. Moreover, certain popular flavours of baking such as cinnamon, vanilla during baking are because of aldehydes.

Aldehydes also play an important part in caramelization of sugars. During the process of caramelization, amino acids convert the aldehyde group present in sugar into unsaturated aldehyde thereby helping in the formation of caramel and the characteristic brown colour of caramel. Aldehydes are also present in herbs such as coriander and give it the characteristic smell of coriander.

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