Carbonyl Compounds (Carbonyl Group)

What are Carbonyl Compounds?

The compounds containing a carbonyl group (the -C=O group) are called carbonyl compounds.

The carbonyl group, C=O, is probably the most important functional group in organic chemistry. These compounds are an integral part of organic chemistry and their primary members are called aldehydes, ketones, and carboxylic acids.

Carbonyl Group

A carbonyl group is a functional group featuring a double bond between a carbon atom and an oxygen atom (illustrated below). However, the term ‘Carbonyl’ can also refer to carbon monoxide as the ligand within an organometallic or inorganic compound (say a metal carbonyl, such as nickel carbonyl).

Carbonyl Compounds

Carbonyl Compounds or Carbonyl Group

Carbonyl compounds can be further divided into organic and inorganic carbonyl compounds.  This article details the with carbonyl compounds those of organic in nature.

Examples of Organic Carbonyl Compounds

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

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Aldehydes, Ketones and Carboxylic Acids

When the carbonyl group is linked to one alkyl or aryl group and one hydrogen atom, the resulting carbonyl compound is called an aldehyde. The general formula of an aldehyde is R-CHO. Ketones are carbonyl compounds in which the carbonyl carbon is linked to two alkyl or aryl groups. Their chemical formulae can be generalized to R-(C=O)-R’. When the carbonyl carbon is bonded to one alkyl/aryl group and one OH group, the resulting carbonyl compound can be classified as carboxylic acid and its chemical formula can be generalized to R-COOH.

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 that 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 examples of ketones are propanone, acetone, 2-methyl-3-pentanone, etc.

Properties of Carbonyl Compounds

Some properties of carbonyl compounds are given below:

  • These are to be polar in nature. They exhibit both positive and 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.

Chemical Reactions of Carbonyl Compounds

The carbon atom of the carbonyl group is said to be electrophilic in nature as they tend to attract electron-rich compounds. Some 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.

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