Organic chemistry. Bridge course

Transcription

1 Organic chemistry Nomenclature of Organic compounds Bridge course

2 Nomenclature of organic compounds There are two systems of naming 1. Trivial system 2. IUPAC system

3 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 Aceticacid id( (acetum vinegar)

4 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.

5 Witi Writing IUPAC name of a compound The IUPAC name of the compound built from 4 parts Prefix word root primary suffix secondary suffix

6 Prefix It denotes the substituent group if present in the organic compound Substituent group prefix F Fluoro Cl Br chloro Bromo

7 substituent prefix I Iodo NO2 Nitro CH3 Methyl C2H5 Ethyl C3H73 7 Propyl

8 Word root It indicates the number of carbon atoms in the longest possiblechain. No. of carbon atoms word root 1 meth 2 eth 3 prop

9 No.of carbon atoms Word root 4 but 5 pent 6 hex 7 hept 8 0ct 9 non 10 dec

10 Primary Suffix It denote the nature of carbon to carbon bond in the organic compounds. ane: bond ene: yne: bond bond

11 Secondary suffix It represents the functional group if present in an organic molecule and is attached hdto the primary suffix while writing the IUPAC name.

12 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 Et Esters COOR 0atet

13 Wii Writing IUPAC name of an aliphatic compound IUPAC= prefix (es)+word root + primary suffix +secondary suffix

14 Eg: H 2 H 3 C CH C 2 1 Word root-:prop CH 3 3 OH Prefix -: methyl Pi Primary suffix-: -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)

15 IUPAC rules for naming organic compounds 1.Longest chain rule: Select the longest continuous chain of carbon atoms known as parent chain CH3-CH-CH2-CH2-CH3 CH3-CH-CH2-CH2-CH3 CH2-CH3CH3 CH2-CH3CH Ethylpentane 3-Methyl hexane (wrong) (correct)

16 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 CH3-CH-CH2-CH3 CH3-CH-CH2-CH3 CH3C CH3C 2 Methylbutane 3 Methylbutane ( correct) (wrong)

17 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 denote the number indicating the substituent attached. CH3 CH3 CH3 CH 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)

18 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 CH3-CH-CH2-CH-CH2-CH3 CH2 CH2 CH3-CH-CH2-CH-CH2-CH3 CH2 CH2 CH3 CH2 CH3 CH2 CH3 CH3 2-Methyl-4-ethylhexane 4-Ethyl-2-methylhexane (wrong) (right)

19 If two different groups are located at the equivalent positions, the numbering should be done in such a way that alkyl group which comes first in the alphabetical order gets the lowest position CH3-CH2-CH-CH-CH2-CH3C C C C C C C2H5 CH3 3-Ethyl-4-methylhexane

20 4: Lowest Number to the Functional Group In case there is a functional group in a molecule, the parent chain is numbered such that the functional group gets the lowest number, even if the lowest number rule is violeted. H 3 C CH 3 C H2 C H C CH H 3 C C 5 4 CH 3 OH 2,2-Dimethylpentan-4-ol wrong CH 3 CH 3 H2 C 3 H C CH 3 2 OH 1 4,4-Dimethylpentan-2-ol Right

21 5 Presence of Identical groups If an organic molecule has more than one functional group, prefixes like di, tri, tetra are used before the suffix indicating the functional group. However, the e of the corresponding alkane is retained H 1 H 3 C CH C CH 2 2 H 2 C 1 CN OH OH OH H 2 C CN 3 4 Butane-1,4-dinitrile Butane-1,2,3-triol

22 Nomenclature of unsaturated hydro carbons H 2 a ) b) H 3 C C C CH 2 H But-1-ene 1 H 3 C C C CH But-2-yne c) H 3 C C C C CH 2 H H H Penta-1,3-diene

23 IUPAC nomenclature of poly functional compound In case of polyfunctional compounds one of the functional group chosen as the principal group and the compound is named on that basis.

24 The order of decreasing priority for functional groups Sulphonicacid>carboxylic acid>ester>acid chloride >amide> nitrile> aldehyde> ketone> alcohol>amine>doublebond>triple bond>ether>other substituents (X>NO2>R) substituent group OHC H 2 C H 2 C H 2 C Formylbutanoicacid COOH principal functional group

25 The IUPAC name of an alicyclic compounds is prefixed with cyclo. NO a) b) c) 1 3 Cyclohexane 3-Nitrocyclohexene 1-Methyl-3-propylcyclohexane

26 Nomenclature of Aromatic compounds a) b) Cl 6 NH CH 3 O 2 N NO C 2 H 5 1-Chloro-2,4-dinitrobenzene 4-Ethyl-2-methylaniline

27 IUPAC names of organic compounds by bond line notation a b But-2-ene 2,3-Dimethylbuta-1,3-diene c d 2,2-Dimethylbutane 3,3-Diethylpentane

28 THANK YOU BRIDGE COURSE 2012