Aldehydes, Ketones, and Carboxylic Acids

Aldehydes, Ketones, and Carboxylic Acids are carbonyl compounds which contain a carbon-oxygen double bond. These organic compounds are very important in the field of organic chemistry and also have many industrial applications.

Aldehydes

Aldehydes are organic compounds which have the functional group -CHO. These carbonyl compounds consist of a central carbonyl carbon doubly bonded to an oxygen and single bonded to the R group (any alkyl group) and a hydrogen atom.

The structure of aldehydes shows an sp2 hybridized central carbon which is doubly connected to an oxygen and has a single bond with hydrogen. The carbonyl center of the aldehyde has an electron withdrawing nature. Therefore, the aldehyde group can be considered somewhat polar.

Small aldehydes are quite soluble in water. Formaldehyde and acetaldehyde are great examples for this. These two aldehydes are quite important industrially. Aldehydes generally exhibit a tendency to undergo oligomerization or polymerization.

Nomenclature of Aldehydes

  • Acyclic and Aliphatic Aldehydes are named after their longest carbon chain along with the “-al” suffix. For example, CH3CH3CH2CHO is called butanal since it has four carbons in the chain.
  • When the aldehyde functional group is added to a ring, the “-carbaldehyde” suffix must be used. For example, C6H11CHO is called cyclohexanecarbaldehyde.
  • In the case of natural compounds or carboxylic acids, “-oxo” is used as a prefix to highlight the carbon which is a part of the aldehyde functional group. For example, (CHO)-CH2COOH is called 3-oxopropanoic acid.

Ketones

Ketones are organic compounds which have the functional group C=O and the structure R-(C=O)-R’. These carbonyl compounds have carbon containing substituents on both sides of the carbon-oxygen double bond.

The carbonyl carbon of the ketone group is sp2 hybridized. The structure of ketones is trigonal planar centered around the carbonyl carbon. The bond angles of this structure approximate at 1200. Since the carbon oxygen bond makes the carbonyl group polar (oxygen is more electron withdrawing than carbon), ketones tend to be nucleophilic at the oxygen atom and electrophilic at the carbon atom.

Ketones are mass-produced industrially for their use as solvents, pharmaceuticals, and as precursors for polymers. Important ketones include methyl ethyl ketone (also called butanone), cyclohexanone, and acetone.

Nomenclature of Ketones

  • Ketones are named after their parent alkanes with the suffix “-anone”. The carbonyl group’s position in the ketone is denoted by a number while naming the ketone. For example, CH3(CO)CH3 is called 2 propanone. However this compound is generally referred to as acetone.
  • Commonly, ketones are named by writing the name of each individual alkyl group attached to the carbonyl carbon and then “ketone” as the third word of the name. For example, butanone can be written as methyl ethyl ketone.

Carboxylic Acids

Carboxylic acids are organic compounds that contain a (C=O)OH group attached to an R group (where R refers to the remaining part of the molecule). The COOH group is commonly referred to as a carboxyl group. Carboxylic acids can generally be expressed via the formula R-COOH.

Carboxylic acids have a polar nature. They can also participate in hydrogen bonding owing to their hydrogen bond accepting nature of the C=O group and the hydrogen bond donating nature of the O-H bond. They generally have higher boiling points when compared to water and tend to form stable dimers.

Carboxylic acids play an important role in the production of pharmaceuticals, food additives, solvents, and polymers. Acetic acid, adipic acid, and citric acid are a few carboxylic acids which are extremely useful industrially.

Nomenclature of Carboxylic Acids

  • Carboxylic acids are named by adding an “-oic acid” suffix to their parent chain. For example, C3H7COOH is called butanoic acid.
  • Even if there are other substituents present, the carboxylic acid can be considered at the first position of the parent chain, as seen in the name for 3-Chloropropanoic acid.
  • The COOH group can also be called “carboxy” and used as a substituent in the name of the parent structure. For example, 2-Furoic acid is commonly referred to as 2-carboxy furan.

To conclude – Aldehydes, Ketones and Carboxylic acids are very important carbonyl compounds industrially as well as in the laboratory. Their nomenclature can be done by following IUPAC guidelines or by following common practices.

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