2.4 Naming carbon chains 23 When a hydrogen atom is removed from a benzene ring this gives a phenyl Do not confuse Ph with pH group (Ph).Related groups include the benzyl group (PhCH2). X ；-c- It is useful to draw a benzene as altemating C=C and C-Cbonds phenyl (CaHa).Ph aryl.Ar benzyl (PhCH2).Bn sthis helps to keep track of mechanisms (Section 7.2) al or p(s) the wavy line indicates wher re the 2.3 Alkyl substitution H R R R-C-H R-C-H R-C-R R-C-R H borndedie to th ee other 2.4 Naming carbon chains The IUPAC name of an organic compound is composed of three parts. Functional groupsare in Section 2.1 Prefix-一Parent--Suffix What su) What is the group? There are four key steps in naming organic compounds 1.Find the longest carbon chain and name this as an alkane.This is the parent name. No.of Carbons Alkane Name No.of Carbons |Alkane Name methane
When a hydrogen atom is removed from a benzene ring this gives a phenyl group (Ph). Related groups include the benzyl group (PhCH2). X phenyl (C6H5), Ph aryl, Ar X = various functional group(s) benzyl (PhCH2), Bn CH2 vinyl allyl the wavy line indicates where the group is joined to the rest of the structure 2.3 Alkyl substitution R C H H H R C R H H R C R R H R C R R R A primary (or 1°) carbon is bonded to one other carbon A secondary (or 2°) carbon is bonded to two other carbons A tertiary (or 3°) carbon is bonded to three other carbons A quaternary (or 4°) carbon is bonded to four other carbons 2.4 Naming carbon chains The IUPAC name of an organic compound is composed of three parts. Prefix Parent Suffix What substituents (e.g. minor functional groups) are on the main chain and where are they? What is the length of the main carbon chain? What is the major functional group? There are four key steps in naming organic compounds. 1. Find the longest carbon chain and name this as an alkane. This is the parent name. No. of Carbons Alkane Name 1 methane No. of Carbons Alkane Name 6 hexane ethane propane butane pentane 2 3 4 5 7 8 9 10 heptane octane nonane decane Do not confuse Ph with pH (Section 1.7) or with phenol, C6H5OH It is useful to draw a benzene ring as alternating CC and CC bonds as this helps to keep track of electron movement in reaction mechanisms (Section 7.2) Functional groups are introduced in Section 2.1 2.4 Naming carbon chains 23
24 Functional groups,nomenclature and drawing organic compounds 2.Identify the major functional group.Replace-ane(in the alkane)with a suffix functional group suffix functional group suffix aldehyde -al ne ine carboxylic acid -oic acid nitrile -nitrile acid (acyl)chloride-oyl chloride 3.Number the atoms in the main chain.Begin at the end nearer the major A branch point is where a carbon functional group and give this the lowest number.For alkanes,begin at the end cathon atoms nearer the first branch point. 4.Identify the substituents(e.g.minor functional groups)on the main chain and their number.Two substituents on the same carbon are given the same number. The substituent name and position is the prefix.The names of two or more different substituents should be included in alphabetical order in the prefix (e.g.hydroxy before methyl). functional group prefix tunctonai group prefix iodo alkane ydroxy amine amino- nitrile cyano- Di-or tri-is used in the e prefix or suffix to indicate the resence e of two or three of the minor or major fu tional groups()respectively. Examples CH3 CI C-OH CH-CHCI 3-methylpentanoic acid 1.2-dichloropropane f the paren OH 0nahopona HG-CH-CHNI CH3 1-aminopropan-2-ol 4-hydroxy-4-methylpentan-2-one
2. Identify the major functional group. Replace -ane (in the alkane) with a suffix. suffix alkene – ene alkyne – yne alcohol – ol amine – amine suffix aldehyde – al ketone –one –oic acid acid (acyl) chloride –oyl chloride carboxylic acid major functional group major functional group nitrile – nitrile Functional group priorities carboxylic acid (RCO2H) > ester (RCO2R) > acid (acyl) chloride (RCOCl) > amide (RCONH2) > nitrile (RCN) > aldehyde (RCHO) > ketone (RCOR) > alcohol (ROH) > amine (RNH2) > alkene (RCH=CHR) > alkane (RH) > ether (ROR) > halogenoalkane (RX) ester –oate 3. Number the atoms in the main chain. Begin at the end nearer the major functional group and give this the lowest number. For alkanes, begin at the end nearer the first branch point. 4. Identify the substituents (e.g. minor functional groups) on the main chain and their number. Two substituents on the same carbon are given the same number. The substituent name and position is the prefix. The names of two or more different substituents should be included in alphabetical order in the prefix (e.g. hydroxy before methyl). minor functional group prefix chloride chloro– bromide bromo– iodide iodo – ketone oxo– prefix alcohol hydroxy – nitro nitro – amine amino– nitrile cyano– minor functional group aldehyde formyl– ether alkoxy – alkene alkenyl– alkane alkyl– Di- or tri- is used in the prefix or suffix to indicate the presence of two or three of the minor or major functional groups (or substituents), respectively. Examples H3 CHCHC 2Cl Cl C CH2 C O CH3 OH H3C CH3 CH2 CHCH 2 C O OH CH3 H3C H3 CHC CH2NH2 OH 3-methylpentanoic acid 1-aminopropan-2-ol 1,2-dichloropropane 5 3 1 3 1 4-hydroxy-4-methylpentan-2-one 1 1 5 3 3 main functional group main functional group 4 2 2 4 2 2 A branch point is where a carbon atom forms bonds to three or four carbon atoms For alcohols, the position of the OH group is sometimes shown at the front of the name of the parent alkane, e.g. 2-propanol For ketones, the position of the CO bond is sometimes shown at the front of the name of the parent alkane, e.g. 2-pentanone 24 Functional groups, nomenclature and drawing organic compounds
2.4 Naming carbon chains 25 2.4.1 Special cases 2.4.1.1 Alkenes and alkynes The position of the double or triple bond is indicated by the number of the lowest carbon atom in the alkene or alkyne. HC=C- -CH=CH2 -C bond is sometimes shown at the front of the name,e.g.2. 4-methylpent-2-ene penten (an examg of a separated by one oc bond) CH 2-methyl-3-butyn-2-ol 2.4.1.2 Aromatics Monosubstituted benzene derivatives are usually named after benzene (C) Reactions of benzene and although some non-systematic or common ames (in brackets)are still used. substituted benzenesare discussed in Chapter/ Name Name benzene chlorobenzene NO2nitrobenzene benzenepni ene cyanobenzene Name han (benz de e nng Disubstituted derivatives are sometimes named using the prefixes ortho-(or positions 2-and 6-),meta-(or positions 3-and 5-)and para-(or position 4-). For trisubstituted derivatives,the lowest possible numbers are used and the prefixes are arranged alphabetically. OH H ortho(o)6 meta(m)5 3 meta(m) para(p) Br OH NO, p-bromophenol 3-0 oro-4-2.4-dinitrotoluene
2.4.1 Special cases 2.4.1.1 Alkenes and alkynes The position of the double or triple bond is indicated by the number of the lowest carbon atom in the alkene or alkyne. H3C CHCHCHCH 3 CH3 3C CCH HO CH3 2C CHCH CH2 CH3 4-methylpent-2-ene 5 3 1 2-methylbuta-1,3-diene (an example of a conjugated diene: two C=C bonds separated by one C–C bond) 1 3 2-methyl-3-butyn-2-ol 1 3 major functional group 4 2 2 4 CH 2 4 2.4.1.2 Aromatics Monosubstituted benzene derivatives are usually named after benzene (C6H6), although some non-systematic or common names (in brackets) are still used. X X H Br NO2 Cl OH CN X CH3 NH2 CH=CH2 Name benzene bromobenzene nitrobenzene chlorobenzene methylbenzene (toluene) hydroxybenzene (phenol) ethenylbenzene (styrene) aminobenzene (aniline) cyanobenzene (benzonitrile) Name CHO X CO2H The word benzene comes first when functional groups of higher priority (than benzene) are on the ring benzenecarboxaldehyde (benzaldehyde) benzenecarboxylic acid (benzoic acid) Name Disubstituted derivatives are sometimes named using the prefixes ortho- (or positions 2- and 6-), meta- (or positions 3- and 5-) and para- (or position 4-). For trisubstituted derivatives, the lowest possible numbers are used and the prefixes are arranged alphabetically. X OH Br CO2H OH Cl CH3 NO2 1 ipso O2N 2 3 4 ortho(o) meta(m) para(p) p–bromophenol 3-chloro-4- 2,4-dinitrotoluene hydroxybenzoic acid ortho(o) 6 meta(m) 5 For alkenes, the position of the CC bond is sometimes shown at the front of the name, e.g. 2- pentene Reactions of benzene and substituted benzenes are discussed in Chapter 7 2.4 Naming carbon chains 25
26 Functional groups,nomenclature and drawing organic compounds Aromatic compounds that contain at least one heteroatom (e.g.O.N or S)as part of the ring are called aromatic het mpounds(heterocycles). Me 43 2 pyrrole furan 2.4-dimethylfuran 2.4.2.3 Esters These are named inw parts.The first part represents the Rgroup aached to oxygen.The second represents the RCO portion which is named as an alkanoate (1.e.the suffix is -oate).A space separates the two parts of the name. The preparation of esters is 0 HaC-CHz-C-O-CHg -R2-c-o56 methyl propanoate Bo-cc ethyl benzoate 2.4.2.4 Amides e prefix.and N-is written before this to show the group is 0 iR2-c HjC-CH2-( _N-CHa R1--prefix 2.4.2.5 Cyclic non-aromatic compounds Alicyclic compounds are cyclic compounds that are not aromatic.(In contrast aliphatic unds that hav e an pounds that hay e a ring of carbon atoms.which h are not aror Conformations ofe are named using the prefix cyclo.For example.cyclobutane is a yclic alkane with The in the r indicate the poition of subtirr number that the smalles OH Br 1 2 3-bromocyclopent-1-ene 2-methylcydopentanone
Aromatic compounds that contain at least one heteroatom (e.g. O, N or S) as part of the ring are called aromatic heterocyclic compounds (heterocycles). N pyridine (a base, commonly used in synthesis) O furan N H pyrrole O Me Me 2,4-dimethylfuran 1 2 34 2.4.2.3 Esters These are named in two parts. The first part represents the Rl group attached to oxygen. The second represents the R2 CO2 portion which is named as an alkanoate (i.e. the suffix is –oate). A space separates the two parts of the name. R2 C O O R1 CH2 C O H3C O CH3 C O O CH2 CH3 First part Second part methyl propanoate 3 1 ethyl benzoate 2.4.2.4 Amides The R1 group is the prefix, and N– is written before this to show the group is attached to nitrogen. R2 C O H N R1 CH2 C O H3C H N CH3 prefix suffix = –amide N-methylpropanamide (a secondary amide) 3 1 2.4.2.5 Cyclic non-aromatic compounds Alicyclic compounds are cyclic compounds that are not aromatic. (In contrast, aliphatic compounds are non-cyclic compounds that have an open chain of atoms.) Cyclic compounds that have a ring of carbon atoms, which are not aromatic, are named using the prefix cyclo. For example, cyclobutane is a cyclic alkane with four carbon atoms. The atoms in the ring are numbered so that the smallest numbers indicate the position of substituents. cyclohexanol 3-bromocyclopent-1-ene Br OH 3 1 2 O CH3 2-methylcyclopentanone 1 2 Reactions of aromatic heterocycles are discussed in Sections 7.10 and 7.11 The preparation of esters is discussed in Section 9.4.2 and their reactions in Section 9.7 Reactions of amides are described in Section 9.8 Primary, secondary and tertiary amides are introduced in Section 2.1 Conformations of cycloalkanes (cyclic alkanes) are discussed in Sections 3.2.3 and 3.2.4 26 Functional groups, nomenclature and drawing organic compounds
2.5 Drawing organic structures 27 Cyclic compounds containing at least one heteroatom (e.g.O.N or S)are examples of heterocyclic compounds (heterocycles). o the cart ad the o-Substitution reactions of n Se 2.5 Drawing organic structures In full structural formula carbon ato C-H bond are sh the nd often the uctures gen and the en are oge e.g chains with C-Cor C=C honds have an shown).Al ximate igza shape (Section .2) or use by ckly drawn, whilst wing all of th mportant parts of th molecule te shape of he mol (Section 1.5) methyl propanoate H C-0-C-H CH CH2CO2CH HH H condensed skeletal full structural formula (E)-but-2-en-1-ol Alkenes like but-eo can exist H these isomers are named =C -C-OH=CH3CH=CHCH2OHOH trans-.or Z-or E-(Section 3.3.1) HH condensed skeletal full structural formula Benzene can be written with a circle within the ring to show the delocalisation of electrons(Section 7.1).However,this does not show the 6 -electrons.which makes drawing reaction mechanisms impossible.A single resonance form, showing the three C=C bonds,is therefore most often used. 一 two equivalent Kekule structures
Cyclic compounds containing at least one heteroatom (e.g. O, N or S) are examples of heterocyclic compounds (heterocycles). O tetrahydrofuran (a cyclic ether; a common solvent) O ethylene oxide (cyclic ether called an epoxide or oxirane) NH O β-propiolactam (a cyclic amide or lactam) β α the carbon adjacent to a C=O bond is called the α- carbon 2.5 Drawing organic structures In full structural formulae, every carbon atom and every CH bond are shown. In condensed structures, the CH bonds, and often the CC bonds, are omitted. In skeletal structures the carbon and hydrogen atoms are not shown and the bonds to hydrogen are usually also not shown (although hydrogen atoms within functional groups, e.g. alcohols, amines, aldehydes and carboxylic acids, are shown). All other atoms are written. These structures are the most useful (and recommended for use by the reader) because they are uncluttered and quickly drawn, whilst showing all of the important parts of the molecule. Skeletal structures are usually drawn to indicate the approximate shape of the molecule, which is determined by the hybridisation of the atoms (Section 1.5). CCC H H H H C H H H OH CCC O O C H H H H H H H H CH3CH=CHCH2OH CH3CH2CO2CH3 O O OH full structural formula condensed skeletal condensed skeletal full structural formula methyl propanoate (E)-but-2-en-1-ol Benzene can be written with a circle within the ring to show the delocalisation of electrons (Section 7.1). However, this does not show the 6 p-electrons, which makes drawing reaction mechanisms impossible. A single resonance form, showing the three CC bonds, is therefore most often used. two equivalent Kekulé structures For epoxide formation and hydrolysis see Section 6.2.2.6 a-Substitution reactions of carbonyl compounds are discussed in Sections 8.4 and 9.10 Carbon chains with CC or CC bonds have an approximate zigzag shape (Section 3.2.2) Alkenes like but-2-en-1-ol can exist as two configurational isomers; these isomers are named cis- or trans-, or Z- or E- (Section 3.3.1) 2.5 Drawing organic structures 27