Science and Technology for UPSC Examinations [Chemistry] Part 14- Basics of Organic Compounds

Carbon Compounds

Cells in our body are made of proteins. The fossil fuels are the important energy resources. The life saving antibiotics and drugs play a vital role in our day to day life. In recent years, many synthetic polymer products like polyethylene terephthalate (PET) polyethylene, nylon, terylene, bakelite, etc. are widely used in various fields.. Soaps, detergents and many cleansing agents are useful for domestic and industrial purposes. The above mentioned products namely, proteins, fossil fuels, antibiotics, drugs, synthetic polymers, soaps and detergents are compounds of carbon. Carbon exhibits a characteristic property called catenation by which carbon atoms can attach themselves with one another and due to this property, a large number of carbon compounds are existing. The role of carbon and its compounds in our daily life shows the importance of the study of these compounds.

Carbon forms a large number of compounds with hydrogen. Compounds containing only carbon and hydrogen are called Hydrocarbons. Many carbon compounds, in addition to hydrogen, also contain some elements like oxygen, nitrogen, halogens (chlorine, bromine and iodine) and sulphur.

What is Organic Molecule?

The difference between organic and inorganic molecules has been a subject of debate. An organic molecule is considered to be a molecule that plays role in organic activities.

• All organic molecules have Carbon.
• Oxygen may or may not be present, for example CH3 (methane) is organic despite not having Oxygen.
• The presence of C–C and C–H bonds are also not needed in some important molecules to call them organic. For example, Urea has no C–H bond. The same is with Oxalic Acid.
• Then C–C bond is neither present in methane, nor in Carbon Tetra Chloride.

Thus, there is no “official” definition of an organic compound. Some textbooks define an organic compound as one containing one or more C-H bonds; others include C-C bonds in the definition. Others state that if a molecule contains carbon-it is organic. One more definition is that except hydrocarbons, organic compounds consists of two parts, namely a reactive part which is known as Functional group and a skeleton of carbon and hydrogen atoms called alkyl radical. Functional group may be defined as an atom or group of atoms which is responsible for the characteristic properties of the compound. The chemical properties of an organic compound are determined by the functional group and the physical properties of an organic compound are determined by the remaining part of the molecule.

Classification of organic compounds based on functional groups

Alcohols

Organic compounds containing -OH as the functional group are known as Alcohols. For example, methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH), Butanol (C₄H₉OH) etc., are alcohols. Most of the characteristic properties of alcohols are due to the presence of the -OH group.

Aldehydes

Organic compounds containing –CHO as the functional group are known as aldehydes. For example, methanal (HCHO), ethanal (CH₃CHO), propanal (CH₃CH₂CHO), butanal (CH₃CH₂CH₂CHO) etc., are aldehydes.

Ketones (>C=O)

Organic compounds containing >C=O as the functional group are known as ketones. For example, propanone (CH₃COCH₃), Butanone (CH₃CH₂COCH₃) are ketones.

Carboxylic acids

Organic compounds containing carboxyl group (-COOH) as the functional group are known as carboxylic acids. For example, methanoic acid (HCOOH), ethanoic acid (CH₃COOH), propanoic acid (CH₃CH₂COOH), butanoic acid (CH₃CH₂CH₂COOH) etc., are carboxylic acids.

Saturation in Organic Chemistry

In organic chemistry, a saturated compound has no double or triple bonds or ring. In saturated hydrocarbons, every carbon atom is attached to two hydrogen atoms, except those at the ends of the chain, which bear three hydrogen atoms. In the case of saturated ethane, each carbon centre has four single bonds as is characteristic of other saturated hydrocarbons, alkanes.

In contrast, in alkenes such as ethylene (C2H4), double bonds are common. Thus, like other alkenes, ethylene is unsaturated. The degree of unsaturation specifies the amount of hydrogen that a compound can bind. The term is applied similarly to the fatty acid constituents of fats, which can be either saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. Unsaturated is used when any carbon structure contains double or occasionally triple bonds. Many vegetable oils contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them. The bromine number is an index of unsaturation.