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IUPAC Nomenclature & Structural Isomerism Contents Topic Page No. Theory 01 - 07 Exercise - 1 08 - 23 Exercise - 2 24 - 26 Exercise - 3 26 - 28 Exercise - 4 29 - 31 Answer Key 32 - 33 Syllabus Hybridisation of carbon; Sigma and pi-bonds; Shapes of simple organic molecules & structural isomerism, IUPAC nomenclature of simple organic compounds (only hydrocarbons, mono-functional and bi-functional compounds); Name : ____________________________ Contact No. __________________ IUPAC NOMENCLATURE & STRUCTURAL ISOMERISM KEY CONCEPTS Classification of organic compounds IUPAC Nomenclature : Groups : Atom or a group of atoms which possess any 'charge' on it or any 'free valency' are called as Groups. Alkyl group : When a hydrogen is removed from saturated hydrocarbon then alkyl group is formed. It is represented by R & its general formula is CnH2n + 1. A bond is vacant on alkyl group on which any functional group may come. CH4 H CH3 – Methyl CH3 – CH3 H CH3 – CH2 – Ethyl (a) C3H7 has following two isomers (i) Normal propyl CH3–CH2–CH2– (ii) Isopropyl (1-methyl ethyl) CH 3–CH– CH3 (b) C4H9 has following four structures : (i) n-butyl H3C–CH2–CH2–CH2– (ii) Iso butyl (2-methyl propyl) CH 3–CH–CH2– CH3 Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 1 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU (iii) Secondary butyl (1-methyl propyl) CH 3–CH2–CH– CH3 CH3 (iv) Tertiary butyl (1,1-dimethyl ethyl) CH3–C– CH3 Alkenyl group : CH2 = CH – Ethenyl CH2 = CH – CH2 – Propenyal CH3 – CH = CH – Propenyl(1-propenyl) CH 3–C=CH2 Isopropenyl (1-methyl-1-ethenyl) C Alkynyl group : CH C– Ethynyl Retained Name : Normal group : (a) It is represented by 'n'. (b) Straight chain of carbon atom is known as normal group. (c) Free bond will come either on 1st carbon atom or on last carbon atom. n-butyl C–C–C–C– n-propyl C–C–C– Iso group : It is represented by following structure C –C– C Neo group : (a) When two methyl group are attached to second last carbon atom group is named as neo group. (b) It is represented by following structure - For eg. Neo pentyl Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 2 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU ALLOTMENT OF IUPAC NOMENCLATURE Table : The Word Root of Unbranched Alkanes Number of Name Carbon Atoms 1 Methane 2 Ethane 3 Propane 4 Butane 5 Pentane 6 Hexane 7 Heptane 8 Octane 9 Nonane 10 Decane 11 Undecane 12 Dodecane 13 Tridecane 14 Tetradecane 15 Pentadecane 16 Hexadecane 17 Heptadecane 18 Octadecane 19 Nonadecane 20 Eicosane 21 Heneicosane 22 Docosane 23 Tricosane 30 Triacontane 31 Hentriacontane 40 Tetracontane 50 Pentacontane 60 Hexacontane 70 Heptacontane 80 Octacontane 90 Nonacontane 100 Centane or Hectane Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 3 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU Rules for Naming the compound having poly functional groups : - If any organic compound possess more than one functional group, then functional group of highest priority is taken in longest chain along with maximum number of substituents. The priority order of the final groups is as under Table : Functional Groups in decreasing order of seniority Class Name Suffix Prefix + ammonio – – ammonium (R4N ) 1. Cations ------------------- + phosphonio – – phosphonium (R4P ) + sulphonio – – sulphonium (R3S ) 2. R – COOH Alkanoic Acid – oic Acid (carboxylic acid) Carboxy 3. Alkane sulphonic Acid – sulphonic Acid sulpho R – SO3H 4. R – C – O – C – R Alkanoic Anhydride – anhydride ------------ || || O O 5. R – COOR Alkyl Alkanoate – alkanoate (carboxylate) Alkoxy carbonyl 6. R – C – X – oyl halide (carbonyl halide) || Alkanoyl halide halo carbonyl O 7. R – C – NH 2 – amide (carboxamide) || Alkanamide Carbamoyl O – nitrile (carbonitrile) cyano 8. R – C N Alkanenitrile 9. R – C – H Alkanal – al (carbaldehyde) formyl || O 10. R – C – R Alkanone – one Oxo / Keto || O 11. Alkanol R – OH – ol hydroxy 12. R – SH Alkanethiol – thiol mercapto Alkanamine – amine amino 13. R – NH2 Isomerism Organic compounds having same molecular formula but differing from each other at least in some physical or chemical properties or both are known as isomers (Berzelius) and the phenomenon is known as isomerism. The difference in properties of isomers is due to the difference in the relative arrangements of various atoms or groups present in their molecules. Isomerism can be classified as follows: Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 4 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU Constitutional or structural isomerism (1) Chain, nuclear or skeleton isomerism : This type of isomerism arises due to the difference in the nature of the carbon chain (i.e., straight or branched) which forms the nucleus of the molecule. Examples : (i) C4H10 : CH3 CH 2 CH 2 CH 3 , CH3 CH CH 3 n Butane | CH3 Isobutane CH3 | (ii) C5H12 : (Three) CH CH CH CH CH , CH CH CH CH , CH C CH 3 2 2 2 3 3| 2 3 3 3 n Pentane | CH3 CH Isopentane 3 Neopentane Except alkynes chain isomerism is observed when the number of carbon atoms is four or more than four. Chain isomers differ in the nature of carbon chain, i.e., in the length of carbon chain. The isomers showing chain isomerism belong to the same homologous series, i.e., functional group, class of the compound (Cyclic or open) remains unchanged. Chain and position isomerism cannot be possible together between two isomeric compounds. If two compounds are chain isomers then these two will not be positional isomers. (2) Position isomerism : It is due to the difference in the position of the substituent atom or group or an unsaturated linkage in the same carbon chain. C3 H6 Cl2 : CH3 CCl 2 CH 3 ,CH3 CH 2 CHCl 2 , CH3 CH CH 2 , CH2 CH 2 CH 2 2,2 Dichloro propane, 1,1 Dichloro propane | | | | (gemdihalide) (gemdihalide) Cl Cl Cl Cl 1,2 Dichloro propane 1,3 Dichloro propane ( , -dihali de) (Vicdihalide) Aldehydes, carboxylic acids (and their derivatives) and cyanides do not show position isomerism. Monosubstituted alicylic compounds and aromatic compounds do not show position isomerism. Structural isomers which differ in the position of the functional group are called regiomers. For example, (i) CH3 CH 2 CH 2 OH (ii) CH3 CH CH 3 | OH Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 5 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU (3) Functional isomerism : This type of isomerism is due to difference in the nature of functional group present in the isomers. The following pairs of compounds always form functional isomers with each other. Examples : (i) Alcohols and ethers (Cn H2n+2O) C2H6O : CH3 CH 2 OH ; H3 C O CH 3 Ethyl alcohol Dimethyl ether C3H8O : CH3 CH 2 CH 2 OH ; C2 H 5 O CH 3 n propyl alcohol Ethyl methyl ether C4H10O : CH3 CH 2 CH 2 CH 2 OH ; CHOCH2 5 2 5 n Butyl alcohol Diethyl ether (ii) Aldehydes, ketones and unsaturated alcohols …etc. (Cn H2nO) O || C3H6O : CH3 CH 2 CHO ; CH3 C CH 3 ; CH2 CH CH 3 ; CH2 CH CH 2 OH Propionaldehyde Acetone Allyl alcohol O 1,2 Epoxy propane (iii) Acids, esters and hydroxy carbonyl compounds …etc. (Cn H2nO2) C2H4O2 : CH3 COOH ; HCOOCH3 Acetic acid Methyl formate O || C3H6O2 : CH3 CH 2 COOH ; CH3 COOCH 3 ; H3C CH CHO ; CH3 C CH 2 OH Propionic acid Methyl acetate 1 Hydroxy propan-2-one OH 2-Hydroxypropanal (iv) Alkynes and alkadienes (C n H2n-2) C4H6 : CH3 CH 2 C CH ; H2 C CH CH CH 2 ; CH3 C C CH 3 ; H2 C C CH CH 3 1 Butyne 1,3 Butadiene 2 Butyne 1,2 Butadiene (v) Nitro alkanes and alkyl nitrites ( NO2 and ONO ) O C2H5NO2 : CHN2 5 ; CHONO2 5 Ethyl nitrite O Nitro ethane (vi) Amines (Primary, secondary and tertiary) H CH3 C3H9N : CH3 CH 2 CH 2 NH 2 ; CH3 CH 2 N ; CH3 CH CH 3 ; CH3 CH 2 N Propan -1- amine | CH3 NH2 CH3 N Methyl ethanamine Propan -2- amine N,N Dimethyl methanamine (vii) Alcohols and phenols CH2OH OH CH3 C7H8O : Benzyl alcohol o-Cresol (viii) Oximes and amides O || C2H5NO : CH3 CH NOH ; CH3 C NH 2 Acetaldoxime Acetamide Physical & Inorganic By Organic Chemistry By A-479 Indra vihar, kota IUPAC NOMENCLATURE AND NV Sir VKP Sir # 6 Ph. - 9982433693 (NV Sir) 9462729791(VKP Sir) STRUCTURAL ISOMERISM B.Tech. IIT Delhi M.Sc. IT-BHU (4) Ring-chain isomerism : This type of isomerism is due to different modes of linking of carbon atoms, i.e., the isomers possess either open chain or closed chain sturctures. C H2 H2C CH2 H2C CH2 C6H12 : ; CHCH3 ; CH CH CH CH CH CH CH2 3 2 2 2 2 H2C 1 Hexene H2C CH2 C Methylcyclopentane H2 Cyclohexane Ring – chain isomers are always functional isomers. (5) Metamerism : This type of isomerism is due to the difference in the nature of alkyl groups attached to the polyvalent atoms or functional group. Metamers always belong to the same homologous series. Compounds like ethers, thio-ethers ketones, secondary amines, etc. show metamerism. CH3 CH2 5 (i) C5H13N : CHN3 7 ; CHN2 5 CH3 CH3 Dimethyl propyl amine Diethyl methyl amine (ii) C6H15N : C3 H 7 NH C 3 H 7 ; C2 H 5 NH C 4 H 9 Dipropyl amine Butyl ethyl amine If same polyvalent functional group is there in two or more organic compounds, then chain or position isomerism is not possible, there will be metamerism e.g., (a) CH3 C CH 2 CH 2 CH 3 ; CH3 CH 2 C CH 2 CH 3 are metamers and not position isomers.
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