iupac nomenclature

IUPAC IUPAC NOMENCLATURNOMENCLATUR

EE

IUPAC SYSTEM OF NOMENCLATUREA system of naming compounds in

chemistry, IUPAC stands for:---International---Union of---Pure and ---Applied---Chemistry

IUPAC System of IUPAC System of Naming Organic Naming Organic

CompoundsCompounds

MR. AJAY KUMAR Sharma

Similarly, the compound H3C CH=CH CH2OH is systematically

named as: CH3

3-Methylbut-2-ene-1-ol

PREFIX WORD ROOT PRIMARY SUFFIX

SECONDARYSUFFIX

PREFIX WORD ROOT

PRIMARY SUFFIX

SECONDARY SUFFIX

So, let us start with THE WORD ROOTTHE 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

Now, let us come to the PRIMARY PRIMARY SUFFIXSUFFIX 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.

But what if both – double and triple bonds are present between the C atoms???

CH C CH2 CH2 CH CH2 hex-1-en-5-

yne

Both ‘ene’ & ‘yne’ are written but –ene comes

before -yne.

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 SUFFIXSUFFIX

FunctionalGroup

Class of compound

Suffix

-COOH Carboxylic acids -oic acid

-COOR Ester -oate

-COX(X=F, Cl, Br, I)

Acyl halides -oyl halide

FunctionalGroup

Class of compound

Suffix

-CONH2 Acid amide -amide

-CN Nitriles -nitrile

-CHO Aldehyde -al

>C=O Ketones -one

-OH Alcohol -ol

-NH2 Amine -amine

-C=C Alkene -ene

-C≡C- Alkyne -yne

Thus the compound, CH3CH2CH2OH is Propanol.

•Prop is the word root.• -ane is the primary suffix.• -ol is the secondary suffixProp+ane+ol = Propanol.

Since the Since the secondary suffix secondary suffix

begins with a vowel begins with a vowel ‘o’, the ‘e’ of –ane is ‘o’, the ‘e’ of –ane is

removed.removed.

As the word indicates, it means something which is fixed orattached before or at the beginning. Hence a prefix is writtenbefore the word root.

These are also of two types: a)) Primary Prefix b)) Secondary Prefix

Let us now come to what we call as PREFIXPREFIX

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 CH3CH2CH2CH3 is

pentane.

CH2

CH2

CH2CH2

CH2

FunctionalGroup

Prefix

-COOH Carboxy-

-SO3H Sulpho-

-COOR Alkoxycarbony-

-COCl Haloformyl-

-CONH2 Carbamoyl-

-CN Cyano-

-CHO Formyl-

>C=O Keto-/oxo-

-OH Hydroxy-

-SH Mercapto-

-NH2 Amino-

Thus the compound: CH3 –– CH –– CH2 –– CH2––

OH

Cl

Word root- ButPrimary suffix- ‘-ane’Secondary suffix- ‘-ol’

Prefix- Chloro

1 2 3 4

IUPAC name, 3-chloro butane-1-ol

Functional group

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-

Note that the word root will come after the prefix. Thus, the

compound ,

is 2-chlorobutane.

CH3 CH CH2 CH3

Cl

Sl no. Substituent Secondary prefix

5 -NO2 Nitro-

6 -NO Nitroso-

7 -N N- Diazo-

8 -OCH3 methoxy

9 -OC2H5 ethoxy

10 -OH Hydroxo

11 -NH2 Amino

Different classes of Organic Compound

HydrocarbonHydrocarbona)a) Saturated hydrocarbonsSaturated hydrocarbons (i) Alkanes

General formula:- CnH2n+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.

Various members of the series are given below:

Formula IUPAC name Common name

CH4 Methane Methane

CH3CH3 Ethane Ethane

CH3CH2CH3 Propane Propane

CH3CH2CH2CH3 Butane n-Butane

CH3(CH2)3CH3 Pentane n-Pentane

CH3(CH2)4CH3 Hexane n-Hexane

(ii) Alkyl radical or Alkyl group(ii) Alkyl radical or Alkyl group General formula:- CnH2n+1

Suffix: -yl1) Alkyl group contains only one H atom less than

the alkane.2) The alkyl group is named by substituting the

suffix ‘ane’ of the name of the corresponding alkane by ‘yl’. For e.g.:-

CH4, Methane becomes CH3- Methyl

Important Alkyl group

(b) Unsaturated hydrocarbons(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:(i) Alkenes(ii) Alkynes

i) AlkenesGeneral formula: CnH2n

Suffix: -ene1) The molecules containing one carbon-carbon

double bonds are called alkenes.2) In IUPAC system, the name of alkenes is derived

by replacing suffix ane of the corresponding alkane by ene.CH3-CH3 CH2=CH2

Ethane Ethene

Some Alkene groupSome Alkene group

ii) alkynesGeneral formula: CnH2n-2

Suffix: -yne1) Alkynes are unsaturated hydrocarbons with

a triple bond between carbon-carbon atom.2) Alkynes are named in the same way as

alkenes i.e., by replacing suffix ane of alkane by yne.

Some Alkyne groupSome Alkyne group

Alkyl halidesAlkyl halides General formula: CnH2n+1X or RX

Prefix: HaloThese 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

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.CH3Cl – chloromethane,

CH3CH2Cl – chloroethane etc.

Alkyl halidesAlkyl halides

alcoholsalcoholsGeneral formula: CnH2n+1OH or ROH

Functional group : -OHSuffix : -ol1) 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

Some alkane and their alcohols

ethersethersGeneral formula: CmH2m+1OCnH2n+1

Functional group: - O -Suffix: -olThese are derived from alkanes by replacing onehydrogen atom by alkoxy group(-OR).For e.g.

methoxy(OCH2)ethoxy(OC2H5) etc.

aldehydesaldehydesGeneral formula:CnH2n+1CHO(where n can be 0 also e.g. HCHO)

Functional group: -CHOSuffix: -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.

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.

aldehydesaldehydes

Aldehydes and their formulasAldehydes and their formulas

KetonesKetonesGeneral formula: CnH2n+1COCmH2m+1

Functional group: >C=OSuffix: -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.

Carboxylic acidCarboxylic acidGeneral formula: CnH2n+1—COOHFunctional group: -COOHSuffix: -oic acid1) 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.

2) In the IUPAC system, they are named by replacing the terminal –e of the corresponding alkane by –oic acid.

aminesaminesGeneral formula: CnH2n+1-NH2

Functional group: -NH2

Suffix: -amineThese 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.

RULES FOR NAMING RULES FOR NAMING AN ORGANIC AN ORGANIC COMPOUNDCOMPOUND

1. Longest chain rule1)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.

CH3CHCH2CH2CH2CH3

CH3 Longest chain

Alkyl group

2. Position of the substituent2. Position of the substituentNumber 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

SubstituentWRONG

CORRECT

3. Lowest set of locant rule3. Lowest set of locant ruleWhen 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 : FUNCTIONAL group followed by DOUBLE BOND, TRIPLE BOND & finally the SUBSTITUENT

We would call it the

FDTS rule!

COOH CH CH CH2 CH2 Cl So in the above compound numbering is

possible as:

COOH CH CH CH2 CH2 Cl

1 2 3 4 5

12345COOH CH CH CH2 CH2 Cl

So which one is the correct numbering according to the

above rule??

3. If you notice in the above example, in SET 1 the functionalgroup is _COOH and it has a Carbon in it. In such cases, the Carbon of the functional group always gets the position no.

1.

4. What if the same functional group exists twice in the chain HOH2C CH2 CH2 CH2OH

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

functionalgroup. 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

1234

Word root Primary Suffix

Locant SecondarySuffix

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.

Let us try naming the compound , which we had taken as an example HOOC CH CH H2C CH2 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

For the same substituent at equivalent position,

the ‘first point of difference’ rule is applicable e.g.

CH3 CH3

H3C C H2C H2C CH CH3 The locant positions are 2,2,5

CH3 in Set 1 and 2,5,5 in Set 2.

CH3 C CH2 CH2 CH CH3

1 2 3 4 5 6

123456CH3

CH3

CH3

Notice that 1st locant is same,in both sets, but 2nd 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.

CH3 CH3

H3C C H2C H2C CH CH3 The locant positions are 2,2,5

CH3 in Set 1 and 2,5,5 in Set 2.

CH3 C CH2 CH2 CH CH3

CH3

CH3

Notice that 1st locant is same,in both sets, but 2nd locant in Set 1 is smaller & hence Set 1 is correct.

CH3

Notice that 1st locant is same,in both sets, but 2nd locant in Set 1 is smaller & hence Set 1 is correct.

6. What if different substituents are present in equivalent position ?

CH3CH2 CH CH CH2CH3

C2H5 CH3

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

RULES FOR NAMING COMPOUNDS HAVING MORE THAN ONE FUNCTIONAL GROUP & /OR SUBSTITUENT &/OR MULTIPLE BOND.

1. 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.

2.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.

S.No. Functional group PREFIX SUFFIX1. -COOH Carboxy- -oic acid2. -SO3H Sulpho- Sulphonic acid3. -COO

-COOAnhydride

4. -COOR Alkoxycarbonyl Alkyl…oate5. -COCl Haloformyl- -oyl chloride6. -CONH2 Carbamoyl- -amide7. -CN Cyano- Nitrile8. -CHO Formyl -al9. >C=O Keto/oxo -one10. -OH Hydroxy- -ol11. -SH Mercapto- -thiol12. -NH2 Amino- -amine

13. >C=O< - -ene14. -C C- - -yne

O

The corresponding prefix and suffix as given earlier for each functional group can be

compiled as the follows:

THANKS FOR YOUR KIND CONSIDERATION

BY:- Ashwani Kumar