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  Organic Chemistry and classification of Organic Molecules, Chemistry tutorial

Introduction:

We all observed that the organic chemistry is fundamentally the chemistry of carbon compounds. Though, if this was not apparent, we can as well state organic chemistry as the study of carbon compounds. The organic chemistry owes its name to the fact that the original compounds studied came from the living things animals or plants. The word 'organic' means things made up from the living things. Over time, the study of organic chemistry has extended to comprise other compounds other than the so-called organic compounds example: plastics, which encompass no direct relation to living matter. Nonetheless, organic chemistry is retained as the umbrella name for the study of compounds of carbon, irrespective of its origin, however excluding the oxides of carbon. Apart from carbon, the organic compounds might have one or more other elements example - hydrogen, oxygen, nitrogen, sulphur and halogens.

The scope of organic chemistry is extremely large, millions of organic compounds have been isolated or prepared, yet the number of guiding principles is comparatively small. The continuing interest and significance of organic chemistry stems from the fact that the organic compounds are necessary for the sustenance of the life example: carbohydrates, proteins, fats, oils and so on. Modern civilization uses huge quantifies of organic compound. Coal, petroleum and natural gas are main sources of carbon compounds for use in production of energy and as starting materials for the preparation of plastics, pesticides, synthetic fibers, dyes, fertilizers, rubbers, detergents, paints, perfumes, medicines and drugs and flavors.

Definition and Scope of Organic Chemistry:

The Organic Chemistry is the study of chemistry of carbon compound, which apart from carbon, might have one or more of hydrogen, oxygen, nitrogen, sulphur and any of the halogens. The carbon compounds are rich in nature all well over 50 percent of all known compounds. The entire living organisms comprised of, manufacture and uses organic or carbon compounds. Millions of organic compounds are recognized and the potential to acknowledge or prepare millions of such compounds is real. The organic compounds are found in and necessary, all features of our lives.

Uniqueness of Carbon Atom:

We are familiar with the organic chemistry as the study of the compounds of carbon. Why is so much chemistry centered on a single element, carbon? Carbon is so exceptional amongst the elements, in that its known compounds are much more abundant than the known compounds of all the other 105 elements put altogether. The carbon atom is an element that consists of six electrons with four in the outermost orbit; and is positioned in period 2 and Group 4 of the Periodic Table. The exceptionality of carbon atom stems from its capability to form:

a) A variety of strong covalent carbon-carbons bond.

b) Long chains or rings of carbon atoms bonded to one other termed as 'Catenation'.

c) Strong covalent bonds by other elements.

d) Multiple bonds (that is, double and triple) by the other carbon atom or other elements.

Illustrations of such bond forming capability are as follows:

871_Types of covalent bond.jpg

Fig: Types of covalent bonds formed by carbon

In all such bonds, carbon exhibits a valency of four. The special properties of carbon can be attributed to its being a relatively small atom by four valence electrons. The energy changes comprised in gaining or losing four electrons, to form a stable configuration, are very high so that simple C4+ and C4- ions don't exist, however customarily, carbon completes its valence-shell octet through sharing electrons (that is, covalent bond formation) by other atoms (that is, carbon or other elements).

Representation of Organic Molecules:

From the above illustration, it must be clear that carbon forms three kinds of covalent bonds: single - double and triple bonds by either itself or with other elements. The covalent bonds are directed in space (that is, spatial arrangement) so that the molecules containing them might be three-dimensional; as for CH4 (methane). It is not simple to represent this spatial arrangement on paper however look at the model below.

750_Three-dimensional structure of the molecule CH4.jpg

Fig: Three-dimensional structure of the molecule CH4

The four single covalent bonds around carbon if equivalent are ordered at the corners of a tetrahedron by the H-C-H bond angles of 109°. In molecules, example: ethene, C2H4, in which the carbon atom is surrounded through two single and one double bond, such a molecule is planar with bond angle of 120°. For molecules example: ethene, C2H2, in which the carbon atom is surrounded through one single and one triple bond, such molecule is collinear with bond angles of 180°.

1490_Directional nature of bonds.jpg

Fig: Directional nature of bonds formed in simple molecules

On paper, either the molecular formula example: CH4 or planar structural formula can be employed for representing molecule.

Classification of Organic Compounds:

We are familiar that the organic compounds are numerous. Though, the number of guiding principles is comparatively small; one of such principles is the categorization of organic compounds as illustrated below:

639_Classification of organic compounds.jpg

Fig: Classification of organic compounds

Open-chain or aliphatic compounds:

These are the compounds which have chains of interlinked carbon atoms (might involve other elements.) The chains length differs over a broad range of carbon atoms example: Pentane, C5H12

2119_Pentane.jpg

Fig: Pentane

Saturated and unsaturated compounds:

Whenever all the bonds between the carbon atoms (might involve other elements) are single, the compound is stated to be saturated example: Pentane. If, though, multiple bonds example: the double bond in alkenes and triple bond in alkynes -C ≡ C - is present in the molecule, the compound is stated to be unsaturated.

Aromatic compound:

These are the carbocyclic compounds endowed with what is termed to as the aromatic character that is, they have rings of carbon atoms, based on the benzene C6H6; that can be illustrated as below:

1383_Benzene.jpg

Fig: Benzene

There are significant differences in properties among the aliphatic and aromatic compounds, example: between hexane C6H12 and benzene, C6H6.

Alicyclic compound:

These are carbocyclic compounds with C-C and/or C = C bonds among the carbon atoms in the ring. Benzene is not generally categorized as alicyclic even although it is carbocyclic. Compounds in this group have several properties identical to those of aliphatic compounds; therefore the name alicyclic.

2487_Alicyclic compound.jpg

Fig: Alicyclic compound

Heterocyclic compounds:

These are the cyclic compounds having elements other than carbon, specifically oxygen, nitrogen or sulphur in the ring example:

2446_Heterocyclic compounds.jpg

Fig: Heterocyclic compounds

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