06/03/2024
KETONES AND ALDEHYDES
A ketone is a functional group that consists of a carbonyl carbon (which is a carbon atom bound to an oxygen atom by a double bond) and two alkyl or aryl groups. Alkyl groups are formed by the removal or abstraction of a hydrogen atom from an alkane, whereas aryl groups are formed as a result of the removal/abstraction of a hydrogen atom from an aromatic ring.
ketone, any of a class of organic compounds characterized by the presence of a carbonyl group in which the carbon atom is covalently bonded to an oxygen atom. The remaining two bonds are to other carbon atoms or hydrocarbon radicals (R).
The ketone functional group is characterized by a carbonyl (C=O) group bound to two hydrocarbons (compounds that comprise only carbon and hydrogen atoms), or any other carbon-containing substituents.
●What is the formula of a ketone?
A ketone consists of two hydrocarbon substituents connected to a carbonyl carbon. The general formula of ketone is CnH2nO, where n represents the number of atoms.
How do you identify a ketone?
The presence of two alkyl/aryl substituents linked to a carbonyl carbon defines ketones. The general structure of a ketone is RCOR. Ketones are identified by their pleasant odor and volatile nature.
CLASSIFICATIONS OF KETONES.
Ketones are classified based on the substituents connected to the carbonyl group.
The two classifications are:
=> Symmetrical ketones
=> Unsymmetrical ketones.
● Symmetrical Ketones
Ketones are said to be symmetrical when both the substituents on the carbonyl group are equivalent,
EXAMPLES OF SYMMETRICAL KETONES are:
▪︎ Acetone (dimethyl ketone)
Acetone is a symmetrical ketone, as it consists of two methyl substituents connected to the carbonyl carbon.
▪︎ Benzophenone (diphenylmethanone)
Benzophenone is also an example of a symmetrical ketone, as it consists of two phenyl groups attached to the carbonyl carbon.
● KETONE COMPOUNDS
Ketone compounds have a wide range of applications both in chemical industries as well as in our day-to-day life. Some of the common ketone compounds are:
▪︎ ACETONE
Acetone is used as a major organic solvent in many organic syntheses.
The cost-effectiveness and volatility of acetone makes it suitable for the cleaning of laboratory glassware.
▪︎ SYNTHESIS OF KETONES
Ketones are synthesized through various methods. Some of the common methods of ketone synthesis are as follows:
▪︎ Oxidation of Alcohols
One of the important methods of ketone synthesis is the oxidation of the secondary alcohols.
ALDEHYDES
Aldehyde, any of a class of organic compounds in which a carbon atom shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms.
The double bond between carbon and oxygen is characteristic of all aldehydes and is known as the carbonyl group. Many aldehydes have pleasant odours, and in principle, they are derived from alcohols by dehydrogenation (removal of hydrogen), from which process came the name aldehyde.
● Oxidation of alcohols
Aldehydes undergo a wide variety of chemical reactions, including polymerization. Their combination with other types of molecules produces the so-called aldehyde condensation polymers, which have been used in plastics such as Bakelite and in the laminate tabletop material Formica. Aldehydes are also useful as solvents and perfume ingredients and as intermediates in the production of dyes and pharmaceuticals. Certain aldehydes are involved in physiological processes. Examples are retinal (vitamin A aldehyde), important in human vision, and pyridoxal phosphate, one of the forms of vitamin B6. Glucose and other so-called reducing sugars are aldehydes, as are several natural and synthetic hormones.
The carbon atoms bonded to the carbonyl group of an aldehyde may be part of saturated or unsaturated alkyl groups, or they may be alicyclic, aromatic, or heterocyclic rings.
● Nomenclature of aldehydes
There are two general ways of naming aldehydes. The first method is based on the system used by the International Union of Pure and Applied Chemistry (IUPAC) and is often referred to as systematic nomenclature. This method assumes the longest chain of carbon atoms that contains the carbonyl group as the parent alkane. The aldehyde is shown by changing the suffix -e to -al. Because the carbonyl group of an aldehyde can only be on the end of the parent chain and, therefore, must be carbon 1, there is no need to use a number to locate it.
In the compound named 4-methylpentanal, the longest carbon chain contains five carbon atoms, and so the parent name is pentane; the suffix -al is added to indicate the presence of the aldehyde group, and the chain is numbered beginning at the carbonyl group. The methyl group is given the number 4, because it is bonded to the fourth carbon of the chain.
The other method of nomenclature for aldehydes, referred to as common nomenclature, is to name them after the common name of the corresponding carboxylic acid; i.e., the carboxylic acid with the same structure as the aldehyde except that ―COOH appears instead of ―CHO. The acids are usually given a name ending in -ic acid. Aldehydes are given the same name but with the suffix -ic acid replaced by -aldehyde. Two examples are formaldehyde and benzaldehyde.
As another example, the common name of CH2=CHCHO, for which the IUPAC name is 2-propenal, is acrolein, a name derived from that of acrylic acid, the parent carboxylic acid.
Properties of aldehydes
The only structural difference between hydrocarbons and aldehydes is the presence in the latter of the carbonyl group, and it is this group that is responsible for the differences in properties, both physical and chemical. The differences arise because the carbonyl group is inherently polar—that is, the electrons that make up the C=O bond are drawn closer to the oxygen than to the carbon. This gives the oxygen a partial negative charge and the carbon a partial positive charge. The polarity of a carbonyl group is often represented using the Greek letter delta (δ) to indicate a partial charge (that is, a charge less than one).
The negative end of one polar molecule is attracted to the positive end of another polar molecule, which may be a molecule either of the same.
●Common examples of aldehydes and ketones.
The general structure of aldehyde is RCHO, and that of the ketone is RCOR, where R is the hydrocarbon part. Examples of aldehyde are acetal (CH3CHO) and propanal (CH3CH2CHO) and that of the ketone are acetone (CH3COCH3) and acetophenone (CH3COC6H5).
An aldehyde is an organic compound in which the carbonyl group is attached to a carbon atom at the end of a carbon chain.
A ketone is an organic compound in which the carbonyl group is attached to a carbon atom within the carbon chain.
