Nomenclature of Unsaturated Hydrocarbons

NOMENCLATURE OF UNSATURATED HYDROCARBONS a) Choose the longest carbon chain with the most unsaturated carbon atoms or the highest number of double or triple bonds, even if it means breaking the earlier rules. 1 2 3 4 5 6 CH3-CH2-C-CH2-CH2-CH2-CH 112 (Correct) CH2 7 (Incorrect) Note: Lowest number is assigned to first unsaturated carbon 1 2 3 4 5 6 CH3-CH=CH-CH2-CH2-CH Hex-2-ene CH3-C-CH2-CH=CH CH2 1 2-Methylpenta-1,4-diene 1 2 3 4 5 HCC-CH2-CH2-CH3 Pent-1-yne 1 2 5 CH3-CC-CH2-CH Pent-2-yne b) Hydrocarbon containing both CC and CC: If a hydrocarbon has both a double bond and a triple bond, it's referred to as alkenynes (not alkynenes). We number the main chain so that the multiple bond (either double or triple) gets the smallest possible number. When these bonds are in equivalent positions, priority is given to the double bond over the triple bond. CH-CC-CH2-CH2-C=CH-CH2-CH 7-Nonen-2-yne 54 CH-CH2-CC-CH-CH=CH2 1-Hepten-4-yne HC≡C-CH2-CH=CH2 (Correct) 1-Penten-4-yne HCC-CH2-CH-CH₂ (Incorrect) Nomenclature of Organic Compounds having functional group(s) Functional Group A functional group is an atom or a group of atoms joined together in a special way within a molecule, and it greatly influences the chemical properties of that molecule. Organic compounds with the same functional group exhibit similar chemical behaviors. For instance, alcohols like CH3OH, C*H_{3}*C*H_{2}*OH ,(CH 3 ) 2 CHOH etc., all release hydrogen when reacted with sodium metal. The existence of a functional group is denoted by adding specific suffixes or prefixes. The table below provides the prefixes and suffixes for various functional groups. Class of Compounds Functional group structure IUPAC group prefix IUPAC group suffix Example Alkanes -ane Butane, CH 3 (C*H_{2}) 2 CH 3 Alkenes X = c < -ene But-1-ene CH2=CHCH2CH3 Alkynes - c =c- -yne But-1-yne CH equiv CCH ,CH, Benzene, Halides Arenes -X (X = F, Cl, Br, I) halo- 1-Bromobutane, CH 3 (CH 2 ) 2 C*H_{2}*Br Alcohols -OH hydroxy- -ol Butan-2-ol, C*H_{3}*C*H_{2} CHOHCH 3 Aldehydes -CHO formyl, or oxo- -al Butanal CH 3 (C*H_{2}) 2 CHO Ketones > c = 0 охо- -one Butan-2-one C*H_{3}*C*H_{2} COCH 3 Nitriles -C-N cyano- nitrile Pentanenitrile. C*H_{3}*C*H_{2}*C*H_{2}*C*H_{2}*CN Ethers alkoxy- -COOH carboxy -oic acid Ethoxyethane, C*H_{3}*C*H_{2}*OC*H_{2}*C*H_{3} Carboxylic acids Carboxylate ions -COO- -oate Esters Sodium butanoate, CH 3 (CH 2 ) 2 CO * O ^ (- N) a^ + Acyl halides -COOR alkoxy carbonyl -oate Methyl propanoate C*H_{2}*C*H_{2} COOCH CH 3 (C*H_{2}) 2 COOH Butanoic acid, -COX Halocarbonyl (X = F, Cl, Br, l) -oyl halide Butanoyl chloride CH 3 (C*H_{2}) 2 COCI Amines -NH2, NH,N- amino- -amine Butan-2-amine, CH 2 CHNH 2 C*H_{2}*C*H_{2} Amides -CONH: -carbamoyl -amide Butanamide, CH 3 (C*H_{2}) 2 CONH 2 Nitro -CONHR, -CONR2 -NO2 Nitro 1-Nitrobutane, CH 3 (C*H_{2}) 3 NO 2 Use the "oxo" prefix when counting the carbon of the aldehyde functional group in carbon chain; otherwise, use "formyl." Here are the guidelines for naming organic compounds with functional groups: 1. Parent Chain The parent chain is the carbon chain containing the functional group, whether or not it forms the longest possible chain. 4 3 4 HC-CH2-CH2-CH-CH2-CH 27 CH2OH Parent Chain For instance, the parent chain may have five carbon atoms instead of six. 2. Numbering the Parent Chain Arrange the chain so that the carbon attached to the functional group gets the lowest number. 2 6 5 3 4 0 113 5 6 2 1 CH3-CH-CH2-C-CH2-CH3 (Correct) (Incorrect) CH3 3. Functional Group Indication Show the presence of a functional group by adding a secondary suffix after the primary suffix (ane, ene, yne). If the secondary suffix starts with 'a', 'i', 'o', 'u', or 'e', omit the 'e' from the primary suffix. CH3COOH Ethanoic acid 0 CH3-CH2-C-CH2-CH3 1 2 5 Pentan-3-one 4. Multiple Functional Groups If there are several functional groups, designate one as the principal functional group. naming it with a suffix. The other functional groups, treated as substituents, are named with prefixes. The principal functional group is chosen based on a preference order. Here is the priority order of certain functional groups, listed from highest to lowest. Functional Groups in Order of Decreasing Priority Class Formula Prefix name (Substituent Name) Suffix (Principal name) Carboxylic acid C-OH Carboxy -oic acid Sulphonic acid -SOH Sulpho Sulphonic acid Carboxylic anhydride C-O-C oic anhydride Ester C-OR Alkoxy carbonyl oate Acylchloride C-CI Halocarbonyl -oyl chloride Amide -C-NH2 Carbamoyl amide Cyanide -CEN Cyano Aldehyde - CHO Formyl nitrile al, carbaldehyde Keto 0 -one 11 C- Alcohol OH Hydroxyl Thiol -SH Mercapto -ol -thiol Amine NH2 Amino -amine Ether 0 Alkoxy All other functional groups like halo (fluoro, chloro, bromo, iodo), nitroso (-NO), nitro (-NO2), alkoxy (-OR), R (alkyl), C₂H₂ (phenyl), and so on are always considered as substituent groups. Examples (i) HOCH(CH2)CH₂COCH 7-Hydroxyhentan-2-One In the above compound, keto group is preferred, so considered as main functional group, whereas hydroxyl group is considered as a substituent. (ii) CH3-CH-CH2-CH2COOH OH 4-Hydroxypentanoic acid (Here -OH group is considered as a substituent (iii) BrCH₂CH = CH₂ 3-Bromoprop-1-ene (Correct) 1-Bromoprop-2-ene (Incorrect) 5. More than one Functional Groups of Same Type If there are multiple functional groups of the same type, show the number by adding "di," "tri," etc., before the class suffix. In such organic compounds, we write the complete name of the parent alkane before the class suffix. Examples (i) CH2(OH)CH2(OH) Ethane-1, 2-diol (ii) CHO-CH2-CH2-CH2-CHO Pentane-1, 5-dial (iii) CH2(OH)CH(OH)CH2(OH) Propane 1, 2, 3-triol If an organic compound has more than one CC or CC, then word root is written as 'alka'. (i) CH2=CH-CH=CH2 Buta-1, 3-diene (ii) CHC-CH=CH-CH=CH-CH Hepta-3, 5-dien-1-yne NOMENCLATURE OF SUBSTITUTED BENZENE COMPOUNDS Monosubstituted Benzene Compounds a) When giving names to benzene compounds with substitutions, just add the prefix of the substituent to the word 'benzene.' Example CH OMe NH NO Br Methylbenzene (IUPAC name) Methoxybenzene Aminobenzene Nitrobenzene Bromobenzene b) Most benzene compounds with substitutions are widely recognized by their common names. OMe NH Toluene Anisole Aniline Disubstituted Benzene Compounds CH When two hydrogen atoms in benzene are swapped with two single atoms or groups, it creates a disubstituted benzene derivative. To identify the positions of these substituents, we number the carbon atoms in the ring, ensuring the substituents get the smallest numbers. There are three possible forms of disubstituted benzene compounds. a) 1, 2 (ortho)-form: If the two substituents are on the carbon atoms next to each other. Br & 1, 2-Dibromo benzene (IUPAC system of nomenclature) Or o-Dibromo benzene (ortho is abbreviated as o) (Trivial system of nomenclature) b) 1, 3 (meta)-form: If the two substituents are on the carbon atoms that are not next to each other, but skip one in between. Br Br 1, 3-Dibromobenzene (IUPAC system of nomenclature). Or m-Dibromo benzene (meta is abbreviated as m) (Trivial system of nomenclature) c) 1, 4 (para)-form: If the two substituents are on carbon atoms that are diagonally positioned to each other. 1, 4-Dibromo benzene (IUPAC system of nomenclature) Or p-Dibromo benzene (para is abbreviated as p) (Trivial system of nomenclature) Tri- or Higher Substituted Benzene Derivatives To name benzene compounds with three or more substitutions, we find the positions of the substitutions on the ring using the lowest locant rule. (i.) A compound with three functional groups is named by considering it as a derivative of the compound where the main functional group is positioned at number 1. Examples: (a) CI ON NO 1-Chloro-2, 4-dinitrobenzene (not 4-chloro-1,3-dinitrobenzene) (b) COOH Br OH 3-Bromo-4-hydroxybenzoic acid (-COOH is the principal functional) (ii) The base compound's suffix is given the number 1, and then we choose the numbering direction so that the following substituent receives the smallest possible number. Examples: a) OH CH 4-lodo-2-methylphenol (-OH is the principal functional group) b) If a substituent, when combined with a benzene ring, gives a special name to the molecule, it is named as a derivative of that molecule with the substituent. OMe CI NH 2CH OH CH 2-Chloro-4-methylanisole CzHs 4-Ethyl-2-methylaniline CH CH 3, 4-Dimethylphenol c) If a benzene ring is connected to a straight-chain molecule with a functional group, it is called a phenyl derivative of that straight-chain compound. Br OH -CH2-CH-CH-CHO 2.3-Dibromopentylbenzene 3-Hydroxy-4-phenylbutanal