Classification of organic compounds. Functional Groups. Nomenclature of organic compounds. Isomerism. Lecture 2. - презентация

1 Classification of organic compounds. Functional Groups. Nomenclature of organic compounds. Isomerism. Lecture 2

2 CLASSIFICATION OF ORGANIC COMPOUNDS I. Classification by structures of organic compounds

3 These compounds are also called as aliphatic compounds and consist of straight end branched chain compounds, for example: 1. Acyclic or open chain compounds Aliphatic compounds straight branched

4 a)Alicyclic Aaliphatic homocyclic cyclic compounds contain carbon atoms joined in the form of a ring. 2. Cyclic or closed chain or ring compounds Aaliphatic heterocyclic cyclic compounds. Sometimes atoms other than carbon are also present in the ring (heterocylic). Tetrahydrofuran given below is an example of this type of compound: These has some of the properties similar to those of aliphatic compounds.

5 1.Benzenoid aromatic compounds b) Aromatic compounds Aromatic compounds are special types of compounds. These include benzene and other related ring compounds (benzenoid). 2. Non-benzenoid compound 3. Heterocyclic aromatic compounds Like alicyclic compounds, aromatic comounds may also have hetero atom in the ring. Such compounds are called hetrocyclic aromatic compounds. Some of the examples of various types of aromatic compounds are:

6 II. Classification by functional groups which include organic compounds Functional Group The functional group is an atom or a group of atoms joined to the carbon chain. Functional Group is responsible for the characteristic chemical properties of the organic compounds. hydroxyl group (–OH) The examples aldehyde group (–CHO) carboxylic acid group (–COOH)

7 Major Classes of Organic Compounds

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11 A group or a series of organic compounds each containing a characteristic functional group forms a homologous series. HOMOLOGOUS SERIES There are a number of homologous series of organic compounds. Some of these are alkanes, alkenes, alkynes, haloalkanes, alkanols, alkanals, alkanones, alkanoic acids, amines etc. The members of the series are called homologues. The members of a homologous series can be represented by general molecular formula and the successive members differ from each other in molecular formula by a - n(–CH 2 )unit. It is also possible that a compound contains two or more identical or different functional groups. This gives rise to polyfunctional compounds

12 Over 16 million carbon-containing compounds are known A systematic method of naming known as the IUPAC (International Union of Pure and Applied Chemistry) nomenclature system is used for identification. In this systematic nomenclature, names are related to structure in such a way that the reader or listener can infer the structure from the name. However, before the IUPAC nomenclature system, organic compounds were named based on their origin or certain properties. For example, citric acid is called NOMENCLATURE OF ORGANIC COMPOUNDS

13 IUPAC NOMENCLATURE IUPAC (International Union of Pure and Applied Chemistry) names: 1- The unbranched alkanes (homologous series) 2- Branched alkanes

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15 Unbranched alkyl groups

16 Butane Propane

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18 NOMENCLATURE OF BRANCHED-CHAIN ALKANES 1- Locate the longest continuous chain of carbon atoms; this chain determines the parent name for the alkane.

19 2- Number the longest chain beginning with the end of the chain nearer the substituent.

20 3- Use the numbers obtained by application of rule 2 to designate the location of the substituent group. The parent name is placed last; the substituent group, preceded by the number indicating its location on the chain, is placed first. 20

21 4. When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain. The substituent groups are listed alphabetically regardless of their order of occurrence in the molecule. Cl is called chloro, Br called bromo, I called iodo, NO 2 called nitro, CN called cyano 21

22 5) When two or more substituents are identical, indicate this by the use of the prefixes di-, tri-, tetra-, and so on. In case of deciding alphabetical order of many substituent disregard multiplying prefixes such asdiand tri, tetra, penta, …. 22

23 6)When two substituents are present on the same carbon, use the number twice.

24 7. When two chains of equal length compete for selection as the parent chain, choose the chain with the greater number of substituents. 24

25 8. When branching occurs at an equal distance from both ends of the longest chain, choose the name that gives the lower number at the first point of difference. 25

26 If any other substituents are found on the parent chain, all these substituents are arranged alphabetically. -NO 2 nitro - NH 2 amino -CN cyano - Cl Chloro -Br bromo - I iodo

27 The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called as isomers. The following flow chart shows different types of isomerism. ISOMERISM Structural Isomerism (structural) isomers: compounds with the same molecular formula but different structure (arrangement of atoms) Compounds having the same molecular formula but different structures (manners in which atoms are linked) are classified as structural isomers. Some typical examples of different types of structural isomerism are given below: (i)Chain isomerism: When two or more compounds have similar molecular formula but different carbon skeletons, these are referred to as chain isomers and the phenomenon is termed as chain isomerism. For example, C5H12 represents three compounds:

28 ifferent isomers are completely different compounds different isomers are completely different compounds have different physical properties such as melting point and boiling point have different physical properties such as melting point and boiling point

29 When two or more compounds differ in the position of substituent atom or functional group on the carbon skeleton, they are called position isomers and this phenomenon is termed as position isomerism. (ii) Position isomerism: For example, the molecular formula C3H8O represents two alcohols:

30 (iii) Functional group isomerism: Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism. For example, the molecular formula C3H6O represents an aldehyde and a ketone: A type of isomerism in which molecular structures differ by the attachment of different groups to the same atom, as in CH3OC3 H7 and C2H5OC2H5 (iv) Metamerism:

31 Structural Formulas for C 4 H 10 O Isomers

32 2 Stereoisomerism The compounds that have the same constitution and sequence of covalent bonds but differ in relative positions of their atoms or groups in space are called stereoisomers. This special type of isomerism is called as stereoisomerism and can be classified as geometrical and optical isomerism