The document discusses the IUPAC system of nomenclature for naming organic compounds. It explains the key concepts of word roots, prefixes, suffixes, functional groups and rules for naming compounds. The longest carbon chain is identified and numbered from the end closest to the first branch or substituent. Functional groups and multiple bonds are given priority in numbering over substituents.

1. IUPAC NOMENCLATURE

2. IUPAC SYSTEM OF NOMENCLATURE A system of naming compounds in chemistry, IUPAC stands for: ---International ---Union of ---Pure and ---Applied ---Chemistry

3. IUPAC System of Naming Organic Compounds

4. MR. AJAY KUMAR Sharma Similarly, the compound H 3 C CH=CH CH 2 OH is systematically named as: CH 3 3-Methylbut-2-ene-1-ol PREFIX WORD ROOT PRIMARY SUFFIX SECONDARY SUFFIX PREFIX WORD ROOT PRIMARY SUFFIX SECONDARY SUFFIX

5. So, let us start with THE WORD ROOT It is the name corresponding to no. of carbon atoms in the longest chain of CARBON atoms in the organic compound. To determine the word root we need to learn the table given alongside. No. of ‘C’ atoms Word Root 1 Meth 2 Eth 3 Prop 4 But 5 Pent 6 Hex 7 Hept 8 Oct 9 Non 10 Dec 11 Undec 12 Dodec

6. Now, let us come to the PRIMARY SUFFIX It indicates the nature of the carbon atom chain selected. primary suffix Only single bonds between C atoms - ane (also called saturated) Presence of double bond between C atoms - ene Presence of triple bond between C atoms - yne If the parent chain contains two, three or more double or triple bonds, then the numerical prefixes such as di (for two) , tri (for three) , tetra (for four) , etc. are added to the primary suffix.

7. But what if both – double and triple bonds are present between the C atoms??? CH C CH 2 CH 2 CH CH 2 hex-1-en-5-yne Both ‘ene’ & ‘yne’ are written but –ene comes before -yne.

8. This is the word that defines the ‘family’ or functional group in the organic compound. The various functional groups with their corresponding suffixes are: Let us now concentrate on the SECONDARY SUFFIX Functional Group Class of compound Suffix -COOH Carboxylic acids -oic acid -COOR Ester -oate -COX (X=F, Cl, Br, I) Acyl halides -oyl halide

9. Thus the compound, CH 3 CH 2 CH 2 OH is Propanol. Prop is the word root. -ane is the primary suffix. -ol is the secondary suffix Prop+ane+ol = Propanol . Since the secondary suffix begins with a vowel ‘o’, the ‘e’ of –ane is removed. Functional Group Class of compound Suffix -CONH 2 Acid amide -amide -CN Nitriles -nitrile -CHO Aldehyde -al >C=O Ketones -one -OH Alcohol -ol -NH 2 Amine -amine -C=C Alkene -ene - C ≡ C- Alkyne -yne

10. As the word indicates, it means something which is fixed or attached before or at the beginning. Hence a prefix is written before the word root. These are also of two types: a)) Primary Prefix b)) Secondary Prefix Let us now come to what we call as PREFIX

11. It is the word which helps us to distinguish between a cyclic and an acyclic compound. The prefix CYCLO is used for cyclic compounds only. Therefore, is cyclopentane while CH 3 CH 2 CH 2 CH 3 is pentane. CH 2 CH 2 CH 2 CH 2 CH 2

12. Thus the compound: CH 3 – CH – CH 2 – CH 2 – OH Cl Word root- But Primary suffix- ‘-ane’ Secondary suffix- ‘-ol’ Prefix- Chloro 1 2 3 4 IUPAC name, 3-chloro butane-1-ol Functional group Functional Group Prefix -COOH Carboxy- -SO 3 H Sulpho- -COOR Alkoxycarbony- -COCl Haloformyl- -CONH 2 Carbamoyl- -CN Cyano- -CHO Formyl- >C=O Keto-/oxo- -OH Hydroxy- -SH Mercapto- -NH 2 Amino-

13. Certain groups in organic chemistry are written as prefixes. They are regarded as substituents. These groups along with their prefixes are as follows: Sl no. Substituent Secondary prefix 1 -F Fluoro- 2 -Cl Chloro- 3 -Br Bromo- 4 -I Iodo-

14. Note that the word root will come after the prefix. Thus, the compound , is 2-chlorobutane. CH 3 CH CH 2 CH 3 Cl Sl no. Substituent Secondary prefix 5 -NO 2 Nitro- 6 -NO Nitroso- 7 -N N- Diazo- 8 -OCH 3 methoxy 9 -OC 2 H 5 ethoxy 10 -OH Hydroxo 11 -NH 2 Amino

15. Different classes of Organic Compound

16. Hydrocarbon Saturated hydrocarbons (i) Alkanes General formula:- C n H 2n+2 Suffix:- ane 1) These are the organic compounds which contain only carbon-carbon single bonds. 2)According to IUPAC system, these are named as alkanes.

17. Various members of the series are given below: n -Hexane Hexane CH 3 (CH 2 ) 4 CH 3 n -Pentane Pentane CH 3 (CH 2 ) 3 CH 3 n -Butane Butane CH 3 CH 2 CH 2 CH 3 Propane Propane CH 3 CH 2 CH 3 Ethane Ethane CH 3 CH 3 Methane Methane CH 4 Common name IUPAC name Formula

18. (ii) Alkyl radical or Alkyl group General formula:- C n H 2n+1 Suffix: - yl Alkyl group contains only one H atom less than the alkane. The alkyl group is named by substituting the suffix ‘ane’ of the name of the corresponding alkane by ‘yl’. For e.g.:- CH 4 , Methane becomes CH 3 - Methyl

19. Important Alkyl group

20. (b) Unsaturated hydrocarbons These are the hydrocarbons which contain carbon to carbon double bonds or carbon to carbon triple bonds in their molecules. These are further classified into two types: Alkenes Alkynes

21. i) Alkenes General formula: C n H 2n Suffix: -ene The molecules containing one carbon-carbon double bonds are called alkenes. In IUPAC system, the name of alkenes is derived by replacing suffix ane of the corresponding alkane by ene. CH 3 -CH 3 CH 2 =CH 2 Ethane Ethene

22. Some Alkene group

23. ii) alkynes General formula: C n H 2n-2 Suffix: -yne Alkynes are unsaturated hydrocarbons with a triple bond between carbon-carbon atom. Alkynes are named in the same way as alkenes i.e., by replacing suffix ane of alkane by yne .

24. Some Alkyne group

25. Alkyl halides General formula: C n H 2n+1 X or RX Prefix: Halo These are obtained from alkanes by the replacement of one or more hydrogen atoms by halogen atoms: RH -> RX (X=F, Cl, Br, I) -H,+X

26. In the IUPAC system, they are named as halogen substituted alkanes i.e., haloalkanes . Thus the name of halogen compound is given by prefixing flouro, Chloro, bromo, iodo to the names of the alkane. For e.g. CH 3 Cl – chloromethane, CH 3 CH 2 Cl – chloroethane etc. Alkyl halides

27. alcohols General formula: C n H 2n+1 OH or ROH Functional group : -OH Suffix : -ol 1) These are derived by replacing one hydrogen atom from an alkane by one hydroxyl group. 2) In IUPAC system, these are called alkanols and their names have been derived by changing -e of corresponding alkane by –ol (alkane-e+ol=alkanol)

28. Some alkane and their alcohols

29. ethers General formula: C m H 2m+1 OC n H 2n+1 Functional group: - O - Suffix: -ol These are derived from alkanes by replacing one hydrogen atom by alkoxy group (-OR). For e.g. methoxy(OCH 2 ) ethoxy(OC 2 H 5 ) etc.

30. aldehydes General formula:C n H 2n+1 CHO(where n can be 0 also e.g. HCHO) Functional group: -CHO Suffix: -al These compounds are obtained by replacing a hydrogen atom attached to the terminal carbon atom in alkane molecule by an aldehydic (CHO) group . The first member is, however, obtained by replacing a hydrogen atom in the hydrogen molecule.

31. These are called alkanals in the IUPAC system of nomenclature and the names of individual members are derived by changing –e of corresponding alkane by –al. aldehydes (alkane - e + al= alkanal)

32. Aldehydes and their formulas

33. Ketones General formula: C n H 2n+1 COC m H 2m+1 Functional group: >C=O Suffix: -one These are obtained by replacing two hydrogen atoms attached to the non-terminal carbon atom in alkane molecule by a divalent oxygen atom. Thus the functional group called ketonic group contains a carbon atom joined to the oxygen atom by double bond. The names of individual members are derived by replacing –e of the corresponding alkane by –one. (alkane - e + one =alkanone)

34. Carboxylic acid General formula: CnH2n+1 — COOH Functional group: -COOH Suffix: - oic acid In this compounds, one hydrogen atom in alkane molecule is replaced by a carboxyl (COOH) group. The first member is, however, obtained by replacing a hydrogen atom in the hydrogen molecule. In the IUPAC system, they are named by replacing the terminal –e of the corresponding alkane by –oic acid. (alkane -e+oic acid= alkanoic acid)

35. amines General formula: C n H 2n+1 -NH 2 Functional group: -NH 2 Suffix: - amine These are the alkyl derivatives of ammonia. They are formed by replacing one, two or all the three hydrogen atoms in ammonia with alkyl radicals. In IUPAC, the name is derived by replacing –e of alkane by amine. (alkane -e+amine= alkanamine)

37. RULES FOR NAMING AN ORGANIC COMPOUND

38. 1. Longest chain rule 1)Determine the longest continuous (not necessarily straight) chain of carbon atoms. The base name corresponds to the number of carbon atoms in the longest chain. The full name for the alkane will include the names of any branches. Longest chain Any chain branching off the longest chain is named as alkyl group or substituent. Alkyl group

39. 2. Position of the substituent Number of the carbon atoms in the parent chain as 1,2,3…etc. starting from the end which gives lower number to the carbon atoms carrying the substituents i.e. Always number from the end of the longest chain closest to the first branch. X X C-C-C-C-C C-C-C-C-C 1 2 3 4 5 5 4 3 2 1 Substituent WRONG CORRECT The number that indicates the positon of the substitunent is called locant

40. 3. Lowest set of locant rule When two or more substituents are present, then end of the parent chain which gives the lowest set of locants is preferred for numbering. Number the chain so as to give the lowest number possible to the : F UNCTIONAL group followed by D OUBLE BOND, T RIPLE BOND & finally the S UBSTITUENT We would call it the FDTS rule!

41. COOH CH CH CH 2 CH 2 Cl So in the above compound numbering is possible as: COOH CH CH CH 2 CH 2 Cl 1 2 3 4 5 1 2 3 4 5 COOH CH CH CH 2 CH 2 Cl CONSIDER AN EXAMPLE:-

42. So which one is the correct numbering according to the above rule?? 3. If you notice in the above example, in SET 1 the functional group is _ COOH and it has a Carbon in it. In such cases, the Carbon of the functional group always gets the position no. 1 .

43. 4. What if the same functional group exists twice in the chain HOH 2 C CH 2 CH 2 CH 2 OH Here, irrespective of the end you start from, you get the same position number both ways. PLEASE be careful not to number the oxygen in the functional group. You only have to number the C atoms in the chain. Hence the compound is, Butane-1,4-diol . WHERE… But + ane + 1,4 - diol 1 2 3 4 Word root Primary Suffix Locant Secondary Suffix

44. NOTE:- The position number of each of the functional groups is expressed by the position number of C-atom to which it is attached and it is known as ‘Locant’. The locants are separated from each other by ‘commas’. The locant and the word are separated by a ‘hyphen’. The numerical prefixes –di, -tri, -tetra etc. are used to indicate the presence of two, three or more like groups .

45. Let us try naming the compound , which we had taken as an example HOOC CH CH H 2 C CH 2 Cl The compound would thus be named as, NOTE:- If the locant is not specified, it is taken as 1 1 2 3 4 5 5-chloropent-2-en-1-oic acid

46. For the same substituent at equivalent position, the ‘first point of difference’ rule is applicable e.g. CH 3 CH 3 H 3 C C H 2 C H 2 C CH CH 3 The locant positions are 2,2,5 CH 3 in Set 1 and 2,5,5 in Set 2. CH 3 C CH 2 CH 2 CH CH 3 1 2 3 4 5 6 1 2 3 4 5 6 CH 3 CH 3 CH 3 Notice that 1 st locant is same, in both sets, but 2 nd locant in Set 1 is smaller & hence Set 1 is correct. For the same substituent at equivalent position, the ‘ first point of difference’ rule is applicable e.g. CH 3 CH 3 H 3 C C H 2 C H 2 C CH CH 3 The locant positions are 2,2,5 CH 3 in Set 1 and 2,5,5 in Set 2. CH 3 C CH 2 CH 2 CH CH 3 CH 3 CH 3 Notice that 1 st locant is same, in both sets, but 2 nd locant in Set 1 is smaller & hence Set 1 is correct. CH 3 Notice that 1 st locant is same, in both sets, but 2 nd locant in Set 1 is smaller & hence Set 1 is correct.

47. What if different substituents are present in equivalent position ? CH 3 CH 2 CH CH CH 2 CH 3 C 2 H 5 CH 3 OPTION A  3-Ethyl-4-methylhexane OPTION B  4-Ethyl-3-methylhexane Hence option A is correct. But ignore multiplying prefixes i.e. di, tri etc. while considering the alphabetical order! What do YOU think would be the correct answer?? When confused about substituents , always remember that we consider the ALPHABETICAL order. OR

48. RULES FOR NAMING COMPOUNDS HAVING MORE THAN ONE FUNCTIONAL GROUP & /OR SUBSTITUENT &/OR MULTIPLE BOND. In a class of students one student is elected as leader, while the others are to follow. Similarly, when more than one functional groups are present, one functional group is chosen as the PRINCIPAL FUNCTIONAL GROUP —written as a suffix , while others are regarded as substituents —written as a prefixes .

49. Now how do we decide the principal functional group?? To remove any confusion, the functional groups are arranged in a preference series as follows: Carboxylic acid > Sulphonic acid > Anhydride > Ester > Acid chloride > Acid amide > Nitrile > Aldehyde > Ketone > Alcohol > Amines > Alkene > Alkyne . The group higher in the preference series is written as a Suffix While the one lower to it would be written as a Prefix .

50. The corresponding prefix and suffix as given earlier for each functional group can be compiled as the follows: O S.No. Functional group PREFIX SUFFIX 1. -COOH Carboxy- -oic acid 2. -SO 3 H Sulpho- Sulphonic acid 3. -COO -COO Anhydride 4. -COOR Alkoxycarbonyl Alkyl…oate 5. -COCl Haloformyl- -oyl chloride 6. -CONH 2 Carbamoyl- -amide 7. -CN Cyano- Nitrile 8. -CHO Formyl -al 9. > C=O Keto/oxo -one 10. -OH Hydroxy- -ol 11. -SH Mercapto- -thiol 12. -NH2 Amino- -amine 13. > C=O < - -ene 14. -C C- - -yne

51. THANKS FOR YOUR KIND CONSIDERATION BY:- Ashwani Kumar