[Chemistry Class Notes] Organic Chemistry – Core Concept and Classification Pdf for Exam

Organic Chemistry is that branch of chemistry that deals with the compounds that have carbon in them. Matters that have Carbon then are called organic compounds. Organic chemistry studies the features characteristics, structure, and reactions of these organic compounds.

By definition, we call those compounds organic that have carbon in them. However, There are certain Carbon compounds that are not organic. Why? Because in these compounds the carbon atom is not bonded with a hydrogen atom. Take the example of CO₂. Here, we see that carbon dioxide has carbon but no hydrogen. Hence, the true definition of organic would be like this – Compounds that have carbon and hydrogen (and other elements) are called organic compounds. But then again Carbon tetrachloride is considered organic despite having no hydrogen. The organic vs inorganic debate will thus see no end.

The Theory of Vitalism 

In the early days – as early as the 17th century – organic compounds were thought to be created only in the bodies of living beings. This is how early chemists used to differentiate between organic and inorganic compounds. However, in 1828 Frederick Woehler accidentally obtained urea from ammonium cyanate – an inorganic compound. Now if you look at the chemical symbol of urea – CH₄N₂O – is a classic example of an organic compound. It has Hydrogen and Carbon. It is produced in our intestines. At the same time, it can be produced artificially as proven by Woehler. So the theory of vitalism is basically an incorrect theory.

Importance of Organic Chemistry 

In order to understand the importance of organic chemistry, you need to understand how we are engulfed by carbon-based materials all around. Literally – you are engulfed by your skin and this skin is made up of carbon. We live in a carbon world – as you have heard this many times. 

Carbon has the following properties:

• Carbon is tetravalent. It has 4 electrons in its valence shell. So, it is always on the lookout for filling up this shell and making the total number of electrons reach 8. Since the carbon electrons are too much attracted by the neutron, it cannot lose electrons easily. Neither can it take electrons from others because of its small size. What it does is, share its electrons with other atoms. The two (or more) atoms use each other’s electrons.

• Since carbon’s neutron(s) has a strong attraction force, it also attracts the electron of the atom whose electrons it is sharing. This strong attraction force keeps the bond between the carbon atom and the other atom strong and stable. As a result, the carbon atom is able to go on making long chains of compounds. These three features of carbon – particularly its long chain-forming nature – are what enable it to form so many compounds.

The clothes you wear are made of carbon. The food you eat is made of carbon. That pet dog that you are caressing is also made of carbon. Your school bus needs carbon to run – petrol is made of carbon. The medicines that people need to get healthy are made of carbon. And things that are made of carbon are all organic materials. So the uses and application of organic materials are vast. Without organic compounds, humanity and human society would not have been there. To deal with these materials, improve them and figure out how we can use these materials for our benefit, we need organic chemistry to examine them closely.

Classification of Organic Compounds  

Organic compounds are mainly classified into two groups: 

Aliphatic compounds are those compounds in which atoms are bonded together to form a chain-like structure. Since the atoms in these compounds do not form a closed loop, the compounds are sometimes called open-chain compounds. Cyclic compounds are those compounds in which the atoms are bonded together in a cyclical form.

Aliphatic Compounds are Further Divided Into –

• Straight chain compounds

• Branched-chain compounds

Straight chain compounds are those that have no atoms (or chemical group as you may call it) attached to the parent chain or the main chain. In other words, the chain of atoms is straight without having any extra branch of atoms replacing some of the hydrogen atoms.

Branched-chain compounds have side chains – extra atoms (or chemical groups) attached to the core body of the compound. The chemical group replaces some of the hydrogens atoms in the core chain and gets attached to it. 

Cyclic Compounds are Further Divided into Two Groups – 

The above two Compounds are Further Divided into Two Groups –

Heterocyclic Aromatic Compounds can Further be Divided into –

The Hybridisation of Organic Compounds 

We know that the carbon has two electrons in the S subshell and two electrons in the P subshell. (Remember when we are talking about the S subshell, we are actually mentioning the 2S subshell or the outer subshell. The inner S subshell should always have 2 electrons) In its original form, the carbon has two S has electrons and two P electrons. So if it were to be bound with another atom – there would be 2 bonds from the S orbital and 2 bonds pertaining to the P orbital.

The thing is, evidence shows that bonds pertaining to carbon do not happen that way. In the excited state, the 2S subshell donates 1 electron to the P subshell. This gives rise to the following scenario – ·        

• The s²p² configuration is changed to s¹p³ configuration and we have a combination of 1S electron and 3P electrons. These electrons are similar or homogeneous in nature. This kind of scenario results in pure sigma bonds.

• Although the S subshell donates one electron to the P subshell, there is one P electron that is unavailable. So in the case of the bonding of two of these kinds of atoms, the two P electrons and one S electrons of each of these atoms will act usually, but the unavailable P electrons in the two will overlap each other’s orbits forming a pi bond.

• If two of the P electrons are unavailable, the single P electron from each of the atoms and the single S electron from each of the atoms will act usually and there will be a sigma bond between the combined S and P shells but there will be the pi bond between each of the unavailable P electrons of each of the atoms. These scenarios are called the hybridization of carbon.

If you read this chapter well, you can actually understand how atomic particles in reality work. Just think about the intricate things that are going on at the atomic level – it is just astounding.

Relevance of Organic Chemistry

Organic Chemistry has to do with the study of life and all those chemical reactions related to our life processes.  People who wish to build a career in Organic Chemistry go on to become doctors, engineers, pharmacologists, scientists, researchers, and the like. All the petty household items such as the ink in your pen, the food colouring, the detergent that you use; are part of Organic Chemistry.  Organic Chemistry is quite useful as a chapter for the students as they get to know about all the major reactions and chemical processes.