Investigate The Relationship Between Structure And Properties Of Oxygen Containing Organic Compounds

We use vinegar in our food. Do you know what is chemical name of vinegar? The chemical name of vinegar is acetic acid. Acetic acid is a carboxylic acid. Carboxylic acids are a class of organic compounds that contain a carboxyl group as their functional group. They are characterized by the presence of a carbon atom double bonded to an oxygen atom and also bonded to a hydroxyl group. The general formula for carboxylic acids is R-COOH. R represents an alkyl group or aryl group. -COOH represents carboxyl group.

Carboxylic acids are named according to following rules. First of all we find the longest continuous chain of carbon atoms that includes the carboxyl group. After that we start numbering the carbon atoms in the parent chain. We start numbering from the carbon atom of carboxyl group. Then we name the number of carbon atoms. For example, if there are two carbon atoms, we name it as ethane. If there are three carbon atoms, we name it as propane. These names are called base names. Remove the final e from the base name and add the suffix -oic acid to the base name.

The carboxyl group in carboxylic acids exhibits polarity due to the presence of the electronegative oxygen atom. Polarity arises from the unequal sharing of electrons in a chemical bond. In the carboxyl group, the oxygen atom is highly electronegative compared to the carbon atom and hydrogen atom. As a result, the oxygen atom pulls the electron density towards itself. Now the oxygen atom has a partial-negative charge. Carbon atom has a partial-positive charge. This separation of charges within the carboxyl group makes it polar.

The hydroxyl group in carboxylic acids is also polar. Carboxylic acids have the ability to form hydrogen bonding due to presence of polar hydroxyl group. In carboxylic acids, the hydrogen atom in the carboxyl group can form hydrogen bonds. These hydrogen bonds undertake a significant role in the distinctive properties and behavior of carboxylic acids.

During boiling, energy is required to overcome the intermolecular forces to convert the compound from a liquid to a gas phase. The intermolecular forces must be broken to allow the molecules to separate and escape into the gas phase. If a compound has stronger intermolecular forces, then greater energy will be required to break these intermolecular forces. As a result compound will have higher boiling point.

The hydrogen bonding in carboxylic acids significantly increases their boiling points. This is because the intermolecular forces between carboxylic acid molecules are stronger due to the presence of hydrogen bonds. A larger amount of energy is needed to break these bonds compared to other intermolecular forces, such as London dispersion forces or dipole dipole interactions.

Carboxylic acids exhibit unique solubility due to the presence of polar carboxyl group and their ability to form hydrogen bonds. Solubility refers to the ability of a substance to dissolve in a particular solvent. Carboxylic acids are generally soluble in water and other polar solvents. This is because the polar carboxyl group readily interacts with the polar solvent molecules through hydrogen bonding.

Generally, as the length of the carbon chain in the carboxylic acid increases, their solubility in water decreases. This is because longer carbon chains have non polar regions. Non polar regions are less compatible with the water molecules that are polar. Therefore they minimize the contact-surface with the water molecules. For example, ethanoic acid is more soluble in water than pentanoic acid.

A dimer is a molecule or chemical species composed of two identical sub-units. These sub-units are joined together through chemical bonds or intermolecular interactions. Carboxylic acids can form dimers through hydrogen bonding between the carboxyl groups of two carboxylic acid molecules. For example, acetic acid dimer is formed through hydrogen bonding between two acetic acid molecules.

Carboxylic acids are acidic in nature. This is due to their ability to easily release hydrogen ions when in a solution. The hydrogen atom is attached to highly electronegative oxygen atom in carboxylic acids. Carboxylic acids can dissociate into carboxylate ion and hydrogen ion due to high polarity of oxygen hydrogen bond.

Carboxylate ion is a resonance stabilized ion. The electron density in carboxylate ion is delocalized between two oxygen atoms. There are two possible resonance structures of carboxylate ion. Carboxylate ions are more acidic than phenol. This is due to greater stability of carboxylate ion as compared to phenoxide ion which is formed by dissociation of phenol.

Phenoxide ion has five resonance structures. Meanwhile carboxylate ion has only two resonance structures. We have studied that greater number of resonance structures means greater stability. Then why is carboxylate ion more stable?.

It is correct to say that stability depends on the number of resonance structures. But the de-localization of electron density between highly electronegative atoms greatly contributes to stability of ion. In phenoxide ion, electron density is de-localized between one highly electronegative oxygen atom and less electronegative carbon atoms. Meanwhile in carboxylate ion, electron density is de-localized between two highly electronegative oxygen atoms. This makes carboxylate ion more stable than phenoxide ion.

The reduction of carboxylic acids involves the conversion of a carboxylic acids to alcohols, aldehydes, or primary alkanes. Carboxylic acids can be chemically reduced to alcohols by using lithium aluminum hydride as a reducing agent. Dilute sulfuric acid is also used in this reaction.

Carboxylic acids can be chemically reduced to aldehydes by using milder reducing agents such as aluminum tri tertiary butoxyhydride. The reduction of a carboxylic acid to an aldehyde involves the removal of one oxygen atom from the carboxyl group. This results in an aldehyde functional group.