Introduction to Organic Chemistry III, Chemistry tutorial

Introduction:

Organic chemistry is the stream of chemistry which comprises the study of structures, composition and synthesis of carbon-containing compounds. In comprehending this kind of chemistry, it is significant to note that all the organic molecules comprise not only carbon, however as well hydrogen. Whereas it is true that the organic compounds can have other elements, the bond between carbon and hydrogen is what forms a compound organic.

Originally, this field was stated as the study of compounds formed by the living organisms; however its definition has been enlarged to comprise artificially synthesized substances too. Before the year 1828, all the organic compounds were obtained from the living organisms. Scientists did not trust it was possible to synthesize organic compounds from inorganic compounds, and numerous who attempted to do so, failed. In the year 1828, though, urea was made from the inorganic substances, paving the way for a latest definition of the organic chemistry.

There are approximately more than 6 million identified organic compounds, and in addition to being abundant, they are as well unique. This is due to the reason that carbon atoms encompass the capability to form strong bonds with numerous different elements. Carbon atoms are as well capable to bond covalently to other the carbon atoms, whereas at the same time forming strong bonds with other non-metal atoms. Whenever carbon atoms bond altogether, they can form chains comprising of thousands of atoms, and also rings, spheres and tubes.

Most of the individuals consider organic chemistry to be extremely complicated and unrelated to everyday life. However the study of this discipline might be complicated, it is very significant to everyday life. Though, organic compounds are a part of everything, from the foods people eat to the products they make use of. They are significant in the creation of plastics, clothing, fibers, insecticides, medications, petroleum-derived chemicals and a long list of products utilized to support life and to make it well-situated.

This branch of study is significant not only to those who are interested in the science-related careers, however to each and every individual alive nowadays and to those who will be born in the future. This is the key in developing new products and enhancing those on which people have become dependent. Each and every year, organic chemists make discoveries which are helpful in enhancing medicines, aiding agricultural development, understanding the human body and performing countless tasks significant to the average person.

Properties of Organic Compounds:

The organic compounds, in general, distinct greatly from the inorganic compounds in seven respects:

1) The organic compounds are generally flammable.

2) Organic compounds, in common, encompass lower boiling and melting points.

3) Organic compounds are generally less soluble in the water.

4) Some of the organic compounds might exist for a given formula. This is termed as isomerism.

5) Reactions of the organic compounds are generally molecular instead of ionic. As an outcome, they are often quite slow.

6) The molecular weights of organic compounds might be extremely high, often well over 1000.  

7) Most of the organic compounds can serve as the source of food for bacteria.

History of Organic Chemistry:

Organic chemistry mainly deals with the compounds of carbon. The science of organic chemistry is considered to have originated in the year 1685 with the publication through Lemery of a chemistry book which categorized substances according to their origin as mineral, vegetable or animal. Compounds derived from the animals and plants became termed as organic and those derived from the non-living sources were inorganic. Till the year 1828 it was assumed that organic compounds could not be formed apart from by living animals and plants. This was termed as the vital-force theory, and belief in it severely limited the growth of organic chemistry. Wohler in the year 1828, by accident, found that application of heat to ammonium cyanate, an inorganic compound, caused it to change to urea, a compound considered organic in nature. This discovery dealt a death blow to the vital-force theory, and via 1850 modern organic chemistry became well established. Nowadays approximately 13 million organic compounds are recognized. Most of these are products of synthetic chemistry, and similar compounds are not acknowledged in nature. Approximately 70,000 organic chemicals are in commercial use.

Difference between Organic and an Inorganic Compound:

Almost certainly the best way is to compare the physical and chemical properties of substances to the table illustrated below. If they concur with such properties on the left column of the table then the substance is most likely organic, whilst if they compare to the properties listed in the right column then the substance is almost certainly inorganic.

1744_Organic and Inorganic Compound.jpg

Fig: Organic and Inorganic Compound

Why does carbon form so many compounds?

Carbon has the capability to bond with itself to make long chains and ring structures; therefore it can form molecules which include from one to an infinite number of C atoms.

Furthermore C atoms might:

Be bonded by multiple bonds (that is, double and triple) and also single.

Have branches of other carbon chains

Require additional atoms joined to them to make them stable. The most common of these is H, however, N, O, X, P and S as well generally takes place attached to C and might even be attached in some different ways.

Note that 'X' is the symbol for any of the halides: F, Cl, Br and I.

Classification of Organic Compounds:

There are millions of organic compounds and this makes it physically impracticable to study each and every individual compound. To facilitate their study, organic compounds are categorized into different groups and sub-groups.

They might be broadly categorized into the given classes:

1) Open chain or acyclic compounds:

Such compounds contain an open chain system of the carbon atoms. The chains might be either straight chains (that is, non-branched or branched). The open chain compounds are as well termed as aliphatic compounds. The name aliphatic is derived from the Greek term aleiphar meaning fats, as the earlier well-known compounds of this class were either obtained from vegetable or animal fats, or had fat like character.

2) Closed chain or cyclic (or ring) compounds:

Such compounds have one or more closed chains (or rings) of atoms and are termed as cyclic or ring compounds. These are of two kinds:

a) Homocyclic compounds or carbocyclic compounds:

The compounds in which the ring comprises of only carbon atoms are known as homocyclic or carbocyclic compounds. The homocyclic compounds or carbocylic compounds are further categorized into:

i) Alicyclic compounds: If a ring of three or more carbon atoms resembling the aliphatic compounds are contained in the homocyclic or carbocyclic compounds, they are known as alicyclic compounds. The saturated alicyclic hydrocarbons encompass the general formula CnH2n.

ii) Aromatic compounds: These carbocylic compounds contain at least one benzene ring that is, a ring of six carbons atoms having alternate double and single bonds. Aromatic compounds are named so because most of them have a fragrant smell.

b) Heterocyclic compounds:

Whenever atoms of more than one type make up the ring in the compounds, they are termed as heterocyclic compounds or heterocycles. In such compounds usually one or more atoms of elements like nitrogen (N), oxygen (O), or sulphur (S) are present. The atom other than that of carbon namely, N, O and S, present in the ring is known as hetero atom. Heterocyclic compounds having five and six atoms in the ring are known as five-membered and six-membered heterocycles correspondingly.

Heterocyclic compounds might be further categorized as monocyclic, bicyclic and tricyclic based on the presence of one, two or three rings in their molecules, correspondingly.

IUPAC Nomenclature of Organic Compounds:

1) Nomenclature of saturated hydrocarbons:

a) Choose the longest continuous chain of carbon atoms in the molecule. The compound is termed as a derivative of this alkane

b) Number the carbon atoms in the parent chain beginning from the end that gives the lowest possible sum for the numbers of the carbon atoms carrying the substituents.

c) The set of locants is preferred, which whenever compared term by term by other set of locants, each in the order of increasing magnitude, consists of the lowest term at the first point of difference.

2) The nomenclature of compounds having functional group or multiple bonds:

a) Choose the longest continuous chain containing the carbon atoms having the functional group or those comprised in the multiple bonds

b) The numbering of atoms in the parent chain is completed in such a manner that the carbon atom bearing the functional group or such carrying the multiple bond gets the lowest possible number.

c) As writing the name of alkene (that is, double bond) or alkyne (that is, triple bond), the primary suffix 'ane' of the corresponding alkane is substituted by 'ene' and 'yne' correspondingly. Though, if the multiple bond takes place twice or thrice in the parent chain, the prefix di- or tri- is joined to the primary suffix ene or yne.

d) In naming the organic compounds having one functional group a suffix named as secondary suffix is added to the primary suffix (giving number of carbon atoms in the chain) to point out the nature of the functional group. Some of the significant secondary suffixes are:

1882_Nature of the functional group.jpg

Fig: Nature of the functional group

Nomenclature of compounds having polyfunctional groups:

Whenever an organic compound includes two or more functional groups, one group is known as the principal functional group whereas the others are known  as the secondary functional groups and are treated as subsituents: The order of preference for principal group is: Carboxylic acid > acid anhydrides > esters > acid halides > amides > nitrites > Aldehydes > ketone > alcohols > amines > double bond > triple bond.

Whenever the functional groups act as substituent, they are termed as:

1526_Functional groups act as substituents.jpg

Fig: Functional groups act as substituent

Nomenclature of simple aromatic compounds:

a) Nuclear substituted: In such, the functional group is directly joined to the benzene ring. Most of such compounds are better known via their common and historical names. In the IUPAC system, they are termed as derivatives of benzene.

b) Side chain substituted: In such, the functional group is present in the side chain of the benzene ring. Both in the common and IUPAC systems, these are generally termed as phenyl derivatives of the corresponding aliphatic compounds.

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