Classification, nomenclature and isomerism

Organic chemistry

1. Introduction to Organic Chemistry

2. Organic chemistry is the study of compounds of carbon. The organic compound is any chemical substance that contains carbon, hydrogen and oxygen. Other compounds may include: Florine Chlorine Bromine Nitrogen Sulphur Phosphorus etc.

3. Classification of Organic compounds Organic compounds Open chain or aliphatic compounds Cyclic compounds Heterocyclic compounds Homocyclic compounds Alicyclic compounds Aromatic compounds Heteroalicyclic compounds

4. Open chain / Acyclic / Aliphatic compounds: Carbon atoms are linked to each other either in linear or branched manner. Eg : Propane Butane Closed Chain / cyclic compounds: These compounds have closed chain of atoms. They are of two types: Homocyclic or Carbocyclic compounds Heterocyclic compounds

5. Homocyclic compounds: The ring structure is made up of only carbon atom. They are of two types: Aromatic compounds Alicyclic compounds Aromatic compounds / benzenoid comounds : Compounds contain one or more benzene rings in their structure. They have pleasant odour . Eg : Monocyclic aromatic ring Polycyclic aromatic ring Benzene Naphthalene Anthracene

6. 2. Alicyclic compounds: Cyclic compounds with ring structure containing only one carbon atoms. They behave more like aliphatic compounds. Eg : Cyclopropane Cyclobutane Cyclopentane

7. Heterocyclic compounds (Non- benzenoid compounds): Cyclic compounds in which the ring atoms are made up of heteroatoms like nitrogen, oxygen and sulphur in addition to carbon. Eg : Pyrrole Furan Thiophene Pyridine Heterocyclic compounds Monocyclic Polycyclic Three membered Bicyclic Four membered Five membered Six membered

8. Monocyclic Heterocyclic compounds: Three membered rings: These rings have two carbon atoms and one hetero atom. Eg : Four membered rings: These rings have three carbon atoms and one hetero atom. These rings are less stable due to strain. Eg : Five membered rings: These rings have four carbon atoms and one hetero atom. Eg :

9. Six membered rings: These rings have five carbon atoms and one hetero atom. Eg : Bicyclic Heterocyclic compounds: These rings contain two ring system, in which atleast one ring contain heteroatom. Eg : Polycyclic Heterocyclic compounds: These rings contain more than two ring system, in which atleast one ring contain heteroatom. Eg :

10. IUPAC system of nomenclature of organic compounds: Common name: The common Name of a compound is one which has a history behind and, is accepted on account of its long usage. Systemic name: The Systematic Name of a compound is based on its structure. IUPAC which is commonly referred to as the IUPAC (International Union of Pure and Applied Chemistry) System of Nomenclature. It was published in 1957 and released in 1967.

11. IUPAC rule for assigning names to complex molecules: Names for Branched-chain hydrocarbons; and Names for other classes of compounds. Naming of Branched chain hydrocarbons: Rule 1: Select the longest continuous carbon chain in the molecule which need not necessarily have to be horizontal (straight). This is called the parent chain or 'main chain', while other chains attached to it are referred to as 'side-chains'. The number of carbon atoms constituting the main chain determines the parent name of the hydrocarbon. As in both the cases longest chain contain six carbon atoms, therefore the parent name of hydrocarbon is Hexane.

12. In case a molecule contain two carbon chains of the same length, the one that carries larger number of branches is designated as: the parent chain. Both structures contain six carbon in long chain, but II shows three branches attached to parent chain. Therefore, the chain shown in II is selected as the parent chain. Rule 2: Number the carbon atom of the parent chain as 1, 2, 3, 4 etc. starting from the end that gives the smallest possible number to the carbons carrying the 8ubstituents or branches.

13. In case there are two or more substituents present on the parent chain, two sets of locants are obtained according as the numbering is done from the left or right. Rule 3: Prefix the name of the substituents to the name of the parent hydrocarbon and indicate its position on the main chain by writing before it the locant . A hyphen (-) is inserted between the locant and the substituent name. the exact name of the substituent methyl group (CH 3 ) is written as 3-methyl.

14. Rule 4: The complete name of the hydrocarbon is written as one word. Hence the hydrocarbon. Name of compound: 3-Methylhexane. In case a number of substituents are present on the main chain, there names are prefixed to the name of the parent hydrocarbon in alphabetical order, inserting hyphen (-) in between the names of substituents . Name of compound: 3-Ethyl-2-methylhexane

15. Rule 5: If the same substituent is present two or more times, this is indicated by prefix di , tri, tetra etc. to the substituent name. The locants of individual substituents are set off from each other by commas and separated from the written name by a hyphen. the names of the substituents are written in alphabetical order regardless of multiplying prefixes di -, trio, etc. Thus ethyl comes before methyl in the name of the following compound the prefix di being neglected for the purpose.

16. Rule 6: In case the substituent on the parent chain is a complex one (containing more than 4 carbon atoms) it is named as a substituted alkyl group whose carbon chain is numbered from the carbon atom attached to the main chain. The name of the complex substituent is given in brackets to avoid confusion with the numbers of the parent chain. Name of compound: 5(1,2-dimethylpropyl) nonane . .

17. Rule 7: The position of a double (or triple) bond in alkenes (or alkynes) is indicated by prefixing the number of the carbon preceding such a bond, the carbon chain being numbered from the end which assigns lower positional number to the double (or triple) bond. In second structure the longest carbon-chain containing double bond has five carbon atoms and, therefore, the name of the hydrocarbon is 2·ethyl-l-pentene. .

18. Names of other classes of compounds: Other classes of compounds - alcohols, aldehydes , ketones , carboxylic acids etc. The compounds belonging to these classes are called functional compounds. Monofunctional compounds: The compounds containing one functional group are referred to as monofunctional . These are named as derivatives of the parent hydrooarbons by the following rules : Rule 1: Select the longest carbon chain bearing the functional group. 'This is the parent chain and is numbered from the end that gives lower positional number to functional group. Rule 2: Write the name of the parent hydrocarbon and prefix the substituent names.

19. Rule 3: Drop the terminat '-e' of the hydrocarbon name and add the suffix assigned to the functional group present. Rule 4: Insert the positional number of the functional group (separated by hyphens on either side) before the name of the parent hydrocarbon. Rule 5: Halo and nitrocompounds are always named as substitutted hydrocarbons. 3,4-Dimethyl-1-hexanol 3-Methyl-1-pentanal 3-Penten-2-one

20. 2-Methyl-3-nitropentane 2-Methyl-1-butanoic acid 2-Methyl-3-hexyn-1-oic acid Polyfunctional compounds: The organic compounds which contain two or more different functional groups in the same molecule, are called Poly functional compounds. Rule 1: When there are many functional groups present in a molecule, only one suffix can be used to form a systematic name. The group named as suffix is termed the Principal group. 3-Hydroxy-1-butanoic acid

21. Rule 2:

22. 2-Bromo-4-hydroxy-1-entanal 4-Amino-2-hexanal 1,2-Epoxy-3-chlopropane 3-Amino-4penten-1-al 3-Cyano-1-pentanoio amine 2-Methylheptene-6-yne

23. STRUCTURAL ISOMERISM Isomers are molecules that have the same molecular formula but differ from each other in physical or chemical properties and the phenomenon is called as Isomerism. Broadly isomerism is of two types: ( i ) Structural Isomerism; and (ii) Stereoisomerism. Structural Isomerism: When the isomerism is simply due to difference in the arrangement of atoms within the molecule, without any reference to space, the phenomenon is termed as Structural Isomerism. Stereoisomerism: When isomerism is caused by the different arrangements of atoms or groups in space, the phenomenon is called Stereoisomerism. The Stereoisomers have the same structural formulas but differ in the spatial arrangement of atoms or groups in the molecule.

24. Classification of Isomerism Isomerism Structural Isomerism Stereio isomerism Chain Isomerism Ring chain Isomerism Positional Isomerism Functional Isomerism Metamerism Tautomerism Geometrical Isomerism Optical Isomerism

25. Chain or Nuclear Isomerism: This type of isomerism arises from the difference in the structure of carbon chain which forms the nucleus of the molecule. It is, therefore, named as Chain or Nuclear Isomerism. Molecular formula: C 4 H 10 Positional Isomerism: When two or more compounds have structural formulas which differ only in the position of the substituent atom or group on the carbon chain, these are called Position Isomers and the phenomenon is termed Positional Isomerism . Molecular formula: C 3 H 7 OH

26. FUNCTIONAL ISOMERISM: When any two compounds have the same molecular formula. but possess different functional groups, they are called Functional Isomers and the phenomenon is termed Functional Isomerism . Molecular formula: C 4 H 8 Molecular formula: C 6 H 4 (CH 3 ) 2 Molecular formula: C 4 H 10 O Molecular formula: C 6 H 6 O

27. METAMERISM: The isomerism caused due to the unequal distribution of carbon atoms on either side of the functional group in the molecule of compounds belonging to the same class is called as Metamerism . Molecular formula: C 4 H 10 O