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Organic Chemistry

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 Sub Topics Chemists believed that compounds obtained from living organisms were enriched with a vital force that distinguished them from inorganic compounds. 'Organic' refers to the compounds that were synthesized from living organisms in the past.  Organic chemistry is the study of hydrocarbons (compounds of carbon and hydrogen) and their derivatives. Nearly all compounds found in living organisms are still classified as organic compounds, as there are many compounds that have been synthesized in the laboratory and have never been found in a living organism. Organic compounds form the basis of all earthly life and constitute a significant part of human endeavors in chemistry. Organic chemistry enables the synthesis of thousands of useful molecules. Organic chemistry has been defined as the chemistry of compound radicals but although we must admit the existence of many such radicals in organic chemistry. Organic chemistry is now considered the chemistry of carbon.

Definition

Every living organism, irrespective of plants and animals are composed of organic compounds and anyone with an interest in life would definitely like to know more about the molecules involved in these life processes, which would require a basic understanding of organic chemistry. Organic chemistry started as the chemistry of life, and then it became the chemistry of carbon compounds, especially those found in coal.

Organic chemistry has always been able to illuminate the mechanism of life by making new molecules that give information not available from the molecules actually present in living things. This creation of new molecules has given new materials such as plastics to make things with, new dyes to cloths, new perfumes and new drugs to cure diseases.
Organic chemistry is the branch of chemistry dealing with compounds containing carbon-carbon bonds. These carbon compounds are special in nature because most of them are covenant in nature and they are highly volatile.

Fundamentals

In earlier days, the branch of chemistry devoted to the study of carbon compounds, whose source was related to the living system was termed as organic chemistry (organic means life).

Organic chemistry is a sub discipline within chemistry involving the scientific study of the structure, properties, composition, reactions and preparation of carbon based compounds, hydrocarbons and their derivatives. These compounds may contain any number of other elements including hydrogen, nitrogen, oxygen the halogens as well as phosphorus, silicon and sulfur.

Nomenclature

Every possible organic compound should have a name from which an unmistakable structural formula can be created. Nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). The names of hydrocarbon molecules are based on the number of carbon atoms that make up the molecule and the type of bond between them.

Organic compounds have been broadly divided into two types:
1. Acylic
2. Cyclic
The first type of compounds is also known as fatty or aliphatic and they have either "normal or branched" structures. The cyclic compounds are either carbocyclic rings containing all carbon atoms or heterocyclic rings containing in addition other atoms also such as N, S or O in ring formation in addition to carbon. The aromatic compounds are a special class of compounds that contain an alternating system of single and double bonds in a six membered planar ring.

Naming organic compounds

For a branched unsaturated acyclic hydrocarbon, the parent chain is the longest carbon chain that contains the maximum number of double and triple bonds. The prefix of the molecule's name is based on number of carbon atoms. For example, a chain of six carbon atoms would be named hex.

There are three methods of naming organic compounds.
1. Trivial names - Trivial names are also called the common names and generally refer to the source of the compounds from which they are obtained.
2. Derived names - Derived names are based on the recognition of certain familiar common names. Thus in alcohol series $CH_3OH$ is called carbinol and $CH_3CH_2OH$ methylcarbinol.
3. Systematic nomenclature - There are numerous organic compounds and impossible to remember the common name of each compound. Therefore a systematic scheme of naming organic compounds is desirable. The first attempt at such a scheme was made in Geneva in 1892. This system is still used nowadays and has been recommended by the International Union of Pure and Applied Chemistry and is thus often refer to as IUPAC nomenclature.

Functional Groups

One of the special features of Organic Chemistry which differentiates it from Inorganic chemistry is that the compounds form a pattern called Homologous series. Every organic compound will have a specific part or group where the reactivity is more. This part is called as functional group in the organic compound.

The properties and reactivity’s of organic molecule are largely determined by the kinds of functional groups. Functional groups are groups of atoms that react in characteristic ways more or less independently of their surroundings. Functional groups contain either heterogeneous or carbon-carbon double or triple bonds. Normally the heterogeneous are halogens or oxygen. Functional groups containing other atoms especially sulfur or phosphorus is also important in organic chemistry.

Reactions

The number and range of organic reactions is so great as to seem bewildering, but actually almost all of them can be fitted into just six categories.
• Substitution
• Addition to double or triple bonds
• $\beta$-elimination
• Rearrangement
• Oxidation and reduction
• Combinations of the above reactions.

Physical Organic Chemistry

Physical chemistry involves both the study of physics and chemistry. Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena applying the principles, practices and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics and dynamics, equilibrium in chemical systems in terms of laws and concepts of physics.

An important goal of physical organic chemistry is to reduce the very complicated results of theoretical, computational and experimental studies of organic reactions to readily understood and teachable principles that explain how molecules react.

In organic chemistry, exciting new discoveries have been made at an increasing pace. To understand organic chemistry we require three passes. First one must familiarize oneself with the physical and chemical properties of organic chemical compounds. The one needs to understand their reactivity’s and their options for reactions. The advanced organic chemistry provides more specialized knowledge and an introduction to retrosynthesis.

Applications

Organic chemistry enables the synthesis of thousands of useful molecules. The application of organic chemistry principles to important biological molecules is integrated where it establishes a bridge with biochemistry courses.

Organic chemistry addresses some of the changes that occur by placing great emphasis on the applications of organic chemistry, especially applications to medicine and agriculture.

Problems

Some of the organic chemistry problems are given below.

Solved Examples

Question 1: Intramolecular hydrogen bonding occurs in cis-1,2-cyclopentanediol but not in the trans isomer. Why?

Solution:
In cis-diol, the hydroxyl groups are close together while in the trans-isomer they are too far apart. The hydroxy groups in the former structure thus can form hydrogen bond easily.

Question 2: What determines the size and shape of atomic orbitals?
Solution:
Atomic orbitals have different sizes and shapes. The size depends on the energy level-size increasing with increasing energy and is defined by the principal quantum number n.
• The s orbitals are spherically symmetrical and so do not have any specific orientation in space; their size increasing with increasing value of n.
• The p orbitals are dumb bell shape with a nodel plane at the middle.
• There are also d orbitals and f orbitals of size and orientations of their own in space.