Organic Compounds

In 1815, Berzelius said that compounds (like  carbohydrates, lipids, proteins, and nucleic acids) obtained from organic substances are called organic compounds and sub minerals are called inorganic substances. This way, compounds were mainly classified into two categories: 

(i) Compounds which are obtained by non-living matter are called Inorganic compounds. 

(ii) Compounds which are obtained by plants and animals are called organic compounds.

Kolbe, in 1845, obtained acetic acid by the combination of C, H, and O, and Berthelot synthesised methane from carbon by the direct combination of carbon and hydrogen. Further, many more compounds continued to be prepared in the laboratory.

The main sources of organic compounds are vegetables and organisms. Organic compounds obtained from the animal kingdom (natural) source or synthesised in the laboratory are impure as they contain related substance, co-product, or reactants. Before qualitative and quantitative estimation of organic compounds, it is essential to obtain it in a pure state. 

After the purification of organic compounds, the various constituent elements present in compounds are qualitatively and quantitatively estimated. Then, the empirical formula, molecular formula, and structural formula of that compound are determined. In addition to it, for the important application (such as medicines etc.) of any known organic compound, it must be essential that they are present in their pure state. 

Thus, to identify any unknown organic compound and to study their various properties, the following stages have to be followed :-

1. Purification
2. Qualitative analysis
3. Quantitative analysis
4. Determination of molecular mass
5. Determination of empirical formula mass 
6. Determination of molecular structure.

Purification of Organic Compounds

In raw state, the compounds are impure and in this state proper study is required. Impurities change the properties of substances and their study in the proper way is not possible.

Organic compounds contain several types of impurities. Some main methods of purification of organic compounds are as follows:

1. Crystallisation
2. Sublimation
3. Distillation
4. Extraction with a solvent or differential extraction
5. Chromatography

Thus, by the determination of melting or boiling point, the purity can be identified. The melting or boiling point of maximum pure compounds is sharp and clear. Modern methods of identification of purity are based on various types of chromatographic and spectroscopic techniques.

Chromatography

It is a modern technique that was discovered by Russian Tswett in 1906 for the separation of constituent components of coloured substances. The word “chromatography” is derived from the Greek word “ma” which refers to colour graphy writing, meaning writing with colours, and later developed by Kuhn, Winterstein, and Karrer on the basis of experimentation. This technique is a recent technique. It is based on the common rate of law of distribution in two phases of various components of any mixture. This method is mainly used for the separation and purification of complex organic substances such as vitamins, hormones, and amino acids in two phases. One phase is the mobile phase and another phase is stationary. Mobile phase may be liquid or gases and the stationary phase may be solid or any liquid. 

Chromatography is mainly of two types:

(a) Adsorption chromatography: In this, the stationary phase is solid and mobile phase is liquid (or gas). It is of two types:

• Column chromatography
• Thin layer chromatography

(b) Partition chromatography: In this, the stationary phase is adsorbed liquid on any inert solid base and the liquid (or gas) passed over it is the mobile phase.

Hybridisation in Carbon Compounds

It is the phenomenon of mixing of orbitals which are the same atom but slightly different in energies so as to form new orbitals with equivalent energy and shape. The new orbitals formed are known as hybrid orbitals. In organic or carbon compounds, s-and p-orbitals are involved by which this form the three types of hybridisation which are

• sp² ( alkenes)        
• sp3 (alkanes)    
• sp (alkynes).

Structure of Alkanes:

Alkanes are the open chain aliphatic hydrocarbons which contain C-C bonds in their molecules. We know that the carbon atom is tetravalent and in alkanes, it is also tetrahedral i.e., it is located in the centre of a regular tetrahedron and its valencies are directed towards its four corners with the bond angles of 109.28°. The structure of methane is (CH4). It lies in the centre of the regular tetrahedron and the four hydrogen atoms attached to it are located at the corners or the vertices of the tetrahedron. Thus, each face of the tetrahedron is an equilateral triangle and has three hydrogen atoms.

Structure of Alkenes: 

Alkenes are open chain aliphatic hydrocarbons containing a carbon-carbon double bond in their molecules. The bond is formed by the sharing of two electrons between the carbon atoms involved in the double bond form. Alkenes are represented by the general formula CnH2n (n=2,3,4 etc. but not 1). Ethene (or ethylene) is the first member of the family with the formula C2H4 Propene (or propylene). The second member of the alkene family has the formula C3H6 .

Structure of Alkynes: 

Alkynes are also open chain aliphatic hydrocarbons with a carbon-carbon triple bond in their molecules. The bond is formed by the sharing of three electrons between the carbon atoms which form triple bonds . Alkynes which use triple bonds have the general formula CnH2n-2 (where n is not equal to 1). Ethyne ( which is also known as acetylene) has the formula of C2H2. The second member of the family is propyne (or methyl acetylene).

The structural formulae of the higher members of the family can be written by assigning different values to n (4, 5, 6,… etc.).

Conclusion

Organic chemistry in which we study about the chemistry of carbon compounds. Several compounds are available in which carbon is present but their behaviour is like inorganic compounds such as carbonate, bicarbonate, carbon dioxide etc.

Alcohol is a hydroxy derivative of hydrocarbons (Alkanes, Alkenes, Alkynes).

Ether is a class of organic compounds in which two alkyl or aryl groups are attached to an oxygen atom; these are represented as R-O-R’.

Phenol is the hydroxy derivative of aromatic hydrocarbons.