O i   h iOrganic chemistry

Nomenclature of Nomenclature of Organic compoundsOrganic compounds

Bridge course

Nomenclature of organic compounds

Th t t f iThere are two systems of naming1 Trivial system1. Trivial system2. IUPAC systemy

Trivial system:

When a few organic compounds were known,g p ,they were named on the basis of their historyor sourceor source.Eg: HCOOH –Formic acid (red ants)

CH3COOH A ti id ( t i )CH3COOH‐Aceticacid (acetum‐vinegar)

IUPAC system:(International Union of Pure and Applied Chemistry)Applied Chemistry)

B   i  thi   t          By using this system one can name any complex organic compound easily.The name assigned to an organic compound on the basis of latest IUPAC prules is known as systematic name.

W iti IUPAC f dWriting IUPAC name of a compoundThe IUPAC name of the compoundpbuilt from 4 partsPrefixPrefixword rootprimary suffixsecondary suffixsecondary suffix

PrefixIt denotes the substituent group if  present in the organic compoundp g p

Substituent group prefixl‐F Fluoro

‐Cl chloroCl chloro‐Br Bromo

substituent prefix‐I                                            IodoNO2                                     Nitro

prefix

‐NO2                                     Nitro‐CH3                                      Methyl‐C2H5                                    Ethyl‐C3H7                                    Propyl 3 7 py

Word rootWord rootIt indicates the number of carbon atoms inthe longest possible chainthe longest possible chain.

N f b dNo. of carbon atoms word root1 meth‐2 eth‐3 prop‐

4 but‐No.of carbon atoms Word root

4 but‐5 pent‐6 hex‐7 hept‐p8 0ct‐9 non‐9 non‐10 dec‐

Primary SuffixIt denote the nature of carbon tocarbon bond in the organiccarbon bond in the organiccompounds.

b dane: bondene: bondyne: bond

S d ffiSecondary suffixIt represents the functional group ifpresent in an organic molecule and is

h d h i ffi hilattached to the primary suffix whilewriting the IUPAC name.

Class of                      functional       secondaryycompounds                 group              suffix

Alcohol                           ‐OH                       ‐olAldehydes                      ‐CHO                     ‐alAldehydes                      ‐CHO                     ‐alKetones                          >C=O                     ‐oneCarboxylic acids           COOH                     oic acidCarboxylic acids          ‐COOH                    ‐oic acidAmines                          ‐NH2                       ‐amineE t                              COOR                     tEsters                            ‐COOR                    ‐0ate

W i i IUPAC fWriting IUPAC name of analiphatic compound

IUPAC     fi  ( ) d  t    i    

aliphatic compound

IUPAC=   prefix (es)+word root + primary   suffix +secondary suffix

Eg: H2g

Word root-: prop CH3

CHH2CH3C OH123

Word root : prop

Prefix -: methylP i ffi

CH3

Primary suffix-: -aneSecondary suffix-: -ol

IUPAC name- 2-Methyl-1-propanolIUPAC name- 2-Methyl-1-propanol

(terminal ‘e’ of the p-suffix is dropped if the sec-suffix begins ith i )with a,e,i,o,u)

IUPAC rules for naming organic compoundscompounds

1.Longest chain rule:Select the longest continuous chain of carbon atomsSelect the longest continuous chain of carbon atomsknown as “parent” chain1 2 3 4 5 3 4 5 6CH3-CH-CH2-CH2-CH3 CH3-CH-CH2-CH2-CH3

| |CH2 CH3 CH2 CH3CH2-CH3 CH2-CH3

2 12-Ethylpentane 3-Methyl hexane2 Ethylpentane 3 Methyl hexane

(wrong) (correct)

2.Lowest number ruleThe carbon chain selected is numbered from the endThe carbon chain selected is numbered from the endnearest to the side chain or substituent so as to give thelowest number to the carbon carrying the side chain.

1 2 3 4 4 3 2 1CH3-CH-CH2-CH3 CH3-CH-CH2-CH3

| |CH3 CH3C C

2‐Methylbutane 3‐Methylbutane( ) ( )( correct) (wrong)

Lowest sum rule:Lowest sum rule:Where there are more than one substituent, numberingof the chain is done in such a way that the sum of theof the chain is done in such a way that the sum of thenumbers assigned to the substituents is minimum.“The term Locant is used to denote the numbere te oca t s used to de ote t e u beindicating the substituent attached”.

CH3 CH3 CH3 CH31 2 | 3 4 | 5 5 4 | 3 2| 1CH3-C-CH2-CH-CH3 CH3-CH-CH2-CH-CH3

| || |CH3 CH3

2,2,4‐trimethylpentane 2,4,4‐trimethylpentane2,2,4 trimethylpentane 2,4,4 trimethylpentaneSet of locants= 2+2+4=8 set of locants=2+4+4=10

(correct) (wrong)

3  Arrangement of Prefixes3. Arrangement of PrefixesIf more than one group is attached to the carbon chain, these groups should be arranged alphabetically. chain, these groups should be arranged alphabetically. When two or more identical substituents are present prefixes like di, tri, tetra, etc. are used. However these prefixes are not considered for alphabetical order.1              2          3             4          5            6                                     1              2        3 4         5              6

CH3-CH-CH2-CH-CH2-CH3 CH3-CH-CH2-CH-CH2-CH3CH3 CH CH2 CH CH2 CH3 CH3 CH CH2 CH CH2 CH3| | | |

CH3          CH2                                      CH3       CH2| || |

CH3 CH3

2-Methyl-4-ethylhexane 4-Ethyl-2-methylhexane(wrong)                                                   (right)

If two different groups are located at the equivalenth b h ld b d hpositions, the numbering should be done in such a

way that alkyl group which comes first in thealphabetical order gets the lowest position.p g p

1 2 3 4 5 6

CH3-CH2-CH-CH-CH2-CH3C C C C C C| |

C2H5 CH3

3-Ethyl-4-methylhexane

4: Lowest Number to the Functional Groupp

In case there is a functional group in a molecule, the parent chain is numbered such that the f ti l    t  th  l t  b    if functional group gets the lowest number, even if the lowest number rule is violeted. 

H3C C

CH3

H2C

HC CH31 2 3 4 5 H3C C

CH3

H2C

HC CH312345

2,2-Dimethylpentan-4-ol 4,4-Dimethylpentan-2-ol

CH3 OH

3

CH3 OH

12345

2,2 Dimethylpentan 4 olwrong

, e y pe oRight

5 Presence of Identical groups5 Presence of Identical groups If an organic molecule has more than one functional 

  fi  lik  di   i       d b f   h  group, prefixes like di, tri, tetra are used before the suffix indicating the functional group. However, the ‘e’ of the corresponding alkane is retainede  of the corresponding alkane is retained.

H3C CHHC CH2

1234H2C CN

12H3C CH C CH2

OH OHOH H2C CN3 4

Butane-1,2,3-triol Butane-1,4-dinitrile

Nomenclature of unsaturated hydro carbons

a ) b)H CH2C C CH H3C C C CH3a ) b)H3C C C

HCH21234

But-1-ene

H3C C C CH31 2 3 4

But-2-yne

H C C C C CH12345

c) H3C CH

CH

CH

CH2

Penta-1,3-diene

c)

IUPAC nomenclature of polyfunctional compoundfunctional compound

In case of polyfunctionalcompounds one of the functionalcompounds one of the functionalgroup chosen as the principal

d th d i dgroup and the compound is namedon that basis.

The order of decreasing priorityfor functional groupsg pSulphonicacid>carboxylic acid>ester>acid chloride>amide> nitrile> aldehyde> ketone>yalcohol>amine>doublebond>triplebond>ether>other substituents (X>NO2>R)

OHCH2C

H2C

H2C COOH

1234 1234

4-Formylbutanoicacidsubstituent group principal functional group

The IUPAC name of an alicyclic compoundsis prefixed with “cyclo”.

NO2

23 1

2) b)

Cyclohexane 3-Nitrocyclohexene

13

a) b) c)

y y1-Methyl-3-propylcyclohexane

Nomenclature of Aromatic compounds

NH2

CH3

2

1

26

Cl

15

6

a) b)

C

34

5NO2O2N 23

4

C2H5

4-Ethyl-2-methylaniline1-Chloro-2,4-dinitrobenzene

IUPAC names of organic compounds b  b d li   iby bond line notation

ba

But-2-ene

b

2,3-Dimethylbuta-1,3-diene

cd

2,2-Dimethylbutane 3,3-Diethylpentane

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BRIDGE COURSE‐2012