Carbonyl Compounds

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What are Carbonyl Compounds?

Carbonyl Compounds definition can be given as the compounds which hold a carbonyl group (which is the C=O group) are known as carbonyl compounds.


The carbonyl group is probably the essential functional group of organic chemistry. These are an integral part of organic chemistry, and their primary members are referred to as ketones, carboxylic acids, and aldehydes.


Carbonyl compounds are further divided into organic and inorganic carbonyl compounds.  This complete article details the carbonyl compounds, which are organic in nature.


What is a Carbonyl Group?

The term carbonyl can also be referred to as carbon monoxide as a ligand, either as a ligand or an organometallic complex (a metal carbonyl, for example, nickel carbonyl).


According to organic chemistry, a carbonyl group can be described as a functional group, which is composed of a double-bonded carbon atom to an oxygen atom: C=O. It is common for many organic compound classes as a part of several larger functional groups. A compound that contains a carbonyl group is often called a carbonyl compound.


Carbonyl Group Structure

The carbonyl structure can be represented as follows:

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Some Organic Carbonyl Compound Examples

A few of the examples of organic compounds include urea, carbamates. The derivatives of phosgene, acyl chlorides chloroformates, carbonate esters, lactones, lactams, isocyanates, hydroxamates.


Aldehydes, Ketones, Carboxylic Acids

When the carbonyl group is linked to either one aryl or an alkyl group and to one hydrogen atom, the resulting carbonyl compound is referred to as an aldehyde. Where the general formula of an aldehyde can be given as R-CHO. Ketones are considered as carbonyl compounds, where the carbonyl carbon is linked to either two aryl or alkyl groups. 


We can generalize their chemical formulae to R-(C=O)-R'. When the carbonyl carbon is bonded to either one alkyl or aryl group, including one OH group, the resultant carbonyl compound is classified as a carboxylic acid. Whereas we can generalize the carbonyl group formula as R-COOH.


Generally, we come to the names aldehydes, ketones when we speak about the Carbonyl compounds. What is the role of these in the carbonyl compounds list? Ketones and Aldehydes are the organic compounds consisting of the functional group same as the carbonyl compounds. The major difference between these compounds is the carbonyl group's position. The carbonyl group in aldehydes is placed at the end of the carbon chain, whereas, coming to ketones, it is located in the middle of the carbon ring. Some examples of aldehydes can be given as butanol, propanol, 4-chlorobutanol, and so on and a few examples considering ketones can be given as acetone, propanone, 2-methyl-3-pentanone, and so on.


Properties of Carbonyl Compounds

A few of the carbonyl compound properties are listed below:

  • Carbonyl Compounds tend to be polar in nature. They exhibit both the positive and negative charges in slight form. Thus, these are known to be polar molecules.

  • Also, these compounds are reported as insoluble in water, but at times, they dissolve other forms of polar molecules.

  • These compounds are said to be chemically reactive compounds, which means that they are allowed to control a chemical reaction.

Chemical Reactions of Carbonyl Compounds

The carbonyl group's carbon atom is known to be electrophilic in nature because they tend to attract electron-rich compounds. A few examples of electrophiles can be given as ions, whereas the oxygen atoms are referred to be nucleophiles because they don't contain a rich density of electrons. They are also said to be the nuclei lovers like the bases. 

The reactions of carbonyl compounds are listed below:

  • Carbonyl Reduction 

This reaction is a process where the Carbonyl groups are reduced by the hydride reagents like the NaBH4 and LiAlH4 with the yeast of the baker or by the catalytic hydrogenation process.

  • Carbonyl alkylation 

This is a process where the carbonyl compounds are alkylated with the organometallic compounds use, such as organolithium reagents, Grignard reagents, acetylides, and more.

  • Carbonyl Alpha-Substitution Reaction 

This substitution reaction type involves the substitution of the α hydrogen atom using `an electrophile.

Carbonyl Compounds Applications

Let us discuss a few applications of carbonyl compounds as listed below:

  • The propanone of carbonyl compounds can be used as a solvent because it gets dissolved in water and other organic solutions.

  • Formaldehyde can be used in the manufacturing of plastics and in biological laboratories for preservation purposes.

  • Butanol is used to provide fragrance for storing the bread fresh.

  • Acetaldehyde can be used as a Synthesizer in various organic reactions.

Spectroscopy of the Carbonyl Group

  • Infrared Spectroscopy  

The double bond of C=O absorbs the infrared light at wavenumbers approximately between 1600–1900 cm−1 (5263 to 6250 nm). The absorption's exact location is well understood concerning the molecule's geometry. When displayed on an infrared absorption spectrum, this absorption is called "carbonyl stretch". Additionally, the propanone's ultraviolet-visible spectra in water give the carbonyl absorption at 257 nm.

  • Nuclear Magnetic Resonance  

The double-bond of C=O exhibits various resonances based on the surrounding atoms, in general, a downfield shift. The carbonyl carbon 13C NMR falls in the range of 160–220 ppm.

FAQ (Frequently Asked Questions)

1. What is Carbonyl Alkylation?

Ans: Carbonyls are alkylated in the nucleophilic addition reactions using the organometallic compounds like acetylides, Grignard reagents, or organolithium reagents. Also, carbonyls can be alkylated using enolates similar to the aldol reactions. Also, carbonyls are the prototypical groups having the vinylogous reactivity (for example, the Michael reaction, where the conjugation's unsaturated carbon with the carbonyl is alkylated instead of carbonyl itself).

2. What is Carbonyl Reduction?

Ans: Carbonyl groups are reduced by the reaction with hydride reagents like LiAlH4 and NaBH4, by the catalytic hydrogenation, or by the yeast of the baker. Ketones form secondary alcohols, while esters, carboxylic acids, and aldehydes form primary alcohols.

3. Is Blood Basic or Acidic?

Ans: The pH value of blood is 7.4, and thus we can say that it is slightly basic.

It is also noted that if the pH value of blood dips to 6 because of abnormal reasons, it can even cause death. So blood should not be acidic.

4. Explain about a Bridging Carbonyl Compound, and How Can We Identify it?

Ans: A bridging carbonyl compound can be described as a ligand that connects either two or more atoms, which are usually called metal ions. The ligand can be either polyatomic or atomic. All the complex organic compounds can serve virtually as the bridging ligands, and hence, usually, the term is restricted to small ligands like ligands or pseudohalides that are specifically designed to link two metals.