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Nomenclature of Organic Compounds

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Nomenclature of Organic Compounds OiOrganic chihemistry Nomenclature of Organic compounds Bridge course Nomenclature of organic compounds There are t wo syst ems of nami ng 1. Trivial system 2. IUPAC system Trivial system: When a few organic compounds were known, they were named on the basis of their history or source. Eg: HCOOH –Formic acid (red ants) CH3COOH‐AtiidAceticacid (t(acetum‐vi)inegar) IUPAC system: (International Union of Pure and Applied Chemistry) 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 rules is known as systematic name. WitiWriting IUPAC name o f a compoun d yThe IUPAC name of the compound built from 4 parts yPrefix yword root yprimary suffix ysecondary suffix Prefix y It denotes the substituent group if present in the organic compound Substituent group prefix ‐FFluoro ‐Cl chloro ‐Br Bromo substituent prefix ‐I Iodo ‐NO2 Nitro ‐CH3 Methyl ‐C2H5 Ethyl ‐C337H7 Propyl Word root y It indicates the number of carbon atoms in the longest possible chain. No. of carbon atoms word root 1meth‐ 2eth‐ 3prop‐ No.of carbon atoms Word root 4 but‐ 5pent‐ 6hex‐ 7hept‐ 80ct‐ 9 non‐ 10 dec‐ Primary Suffix yIt denote the nature of carbon to carbon bond in the organic compounds. yane: bdbond yene: bond yyne: bond Secon dary su ffix It represents the functional group if present in an organic molecule and is attachdhed to theprimary suffixwhile writing the IUPAC name. Class of functional secondary compounds group suffix Alcohol ‐OH ‐ol Aldehydes ‐CHO ‐al Ketones >C=O ‐one Carboxylic acids ‐COOH ‐oic acid Amines ‐NH2 ‐amine EtEsters ‐COOR ‐0ate WiiWriting IUPAC name of an aliphatic compound IUPAC= prefix ()(es)+word root + primary suffix +secondary suffix Eg: H2 H3C CH C OH 3 2 1 Word root -:prop: prop CH3 Prefix -: methyl PiPrimary su ffix-: -ane Secondary suffix-: -ol IUPAC name- 2-Methyl-1-propanol (terminal ‘e’ of the p-suffix is dropped if the sec-suffix begins with a,e,i ,o,u) IUPAC rules for naming organic compounds 1.Longest chain rule: Select the longest continuous chain of carbon atoms known as “parent” chain 12345 3456 CH3-CH-CH2-CH2-CH3 CH3-CH-CH2-CH2-CH3 || CH2-CH3 CH2-CH3 21 2-Ethylpentane 3-Methyl hexane (wrong) (correct) 2.Lowest number rule The carbon chain selected is numbered from the end nearest to the side chain or substituent so as to give the lowest number to the carbon carrying the side chain. 1234 4321 CH3-CH-CH2-CH3 CH3-CH-CH2-CH3 || CH3 CH3 2‐Methylbutane 3‐Methylbutane ( correct) ()(wrong) Lowest sum rule: Where there are more than one substituent, numbering of the chain is done in such a way that the sum of the numbers assigned to the substituents is minimum. “The term Locant is used to den ote ttehe nuubember indicating the substituent attached”. CH3 CH3 CH3 CH3 12| 34| 554| 32| 1 CH3-C-CH2-CH-CH3 CH3-CH-CH2-CH-CH3 | | CH3 CH3 2,2,4‐trimethylpentane 2,4,4‐trimethylpentane Set of locants= 2+2+4=8 set of locants=2+4+4=10 (correct) (wrong) 3. Arrangement of Prefixes If more than one group is attached to the carbon 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 34 5 6 CH3-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) y If two different groups are located at the equivalent positions, thenumbering shldhould be done in such a way that alkyl group which comes first in the alphabetical order gets the lowest position. 12 3456 CH3-CH2-CH-CH-CH2-CH3 | | C2H5 CH3 3-Ethyl-4-methylhexane 4: Lowest Number to the Functional Group y In case there is a functional group in a molecule, the parent chain is numbered such that the ftilfunctional group gets the ltlowest number, even if the lowest number rule is violeted. CH3 CH3 H2 H H2 H H3CCC C CH3 12 3 45 H3CCC C CH3 5 4 3 2 1 CH3 OH CH3 OH 2,2-Dimethylpentan-4-ol 4,4-Dimethylpentan-2-ol wrong Right 5 Presence of Identical groups If an organic molecule has more than one functional group, prefixes like di, tri, tetra are used bfbefore the suffix indicating the functional group. However, the ‘e’ of the corresponding alkane is retained. 4 3 2H 1 2 1 H CCN H3C CH C CH2 2 H C CN OH OH OH 2 3 4 Butane-1,2,3-triol Butane-1,4-dinitrile Nomenclature of unsaturated hydro carbons H2 a ) H C C C CH b) H3C C C CH3 3 2 1 2 4 3 H2 1 34 But-1-ene But-2-yne 5 4 3 2 1 c) H3C C C C CH2 H H H Penta-1,3-diene IUPAC nomenclature of poly functional compound In case of polyfunctional compounds one of the functional group chosen as the principal group and thecompound isnamed on that basis. The order of decreasing priority for functional ggproups Sulphonicacid>carboxylic acid>ester>acid chloride >amide> nitrile> aldehyde> ketone> alcohol>amine>doublebond>triple bond>ether>other substituents (X>NO2>R) H2 H2 H2 OHC C C C COOH 4 3 2 1 substituent group principal functional group 4-Formylbutanoicacid The IUPAC name of an alicyclic compounds is prefixed with “cyclo”. NO2 3 1 2 2 a) b) c) 3 1 Cyclohexane 3-Nitrocyclohexene 1-Methyl-3-propylcyclohexane Nomenclature of Aromatic compounds NH2 6 Cl 1 5 CH3 1 b) a) 6 2 2 O N 4 NO 5 3 2 3 2 4 C2H5 1-Chloro-2,4-dinitrobenzene 4-Ethyl-2-methylaniline IUPAC names of organic compounds by bbdond line notation a b But-2-ene 2,3-Dimethylbuta-1,3-diene d c 2,2-Dimethylbutane 3,3-Diethylpentane THANK YOU BRIDGE COURSE‐2012.
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