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IUPAC NOMENCLATURE OF COMPOUNDS CONTAINING MORE THAN ONE FUNCTIONAL GROUP

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IUPAC NOMENCLATURE OF COMPOUNDS CONTAINING MORE THAN ONE FUNCTIONAL GROUP
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  CHAPTER-III IUPAC NOMENCLATURE OF COMPOUNDSCONTAINING MORE THAN ONE FUNCTIONAL GROUP Based on whether a group can be used as suffix in the root name(as parent compound)or as prefix before the parent name(as branches), functional groups belong to the followingthree types. TYPE A :   Groups which can be used only as prefix i.e as a substituent: Name of the groupGeneral formula alkylR-alkoxyRO-alkylsulfanyl(alkylthio)RS-haloX-nitroNO 2 -alkenyl  R CH CH alkynyl  R C C  phenylC 6 H 5 -cycloalkylcyclopropyl, cyclobutyl etc.These 9 types of groups are used only as branches of the main chain. In otherwordsthey are used only as prefixes to the parent compounds. They are never used as suffixes of the root words to form the parent compounds. Therefore, they do not have any priority order among them. Lowest set of locants rule is applicable to all of them to choose the directionof numbering the longest chain. CAUTION  : The order in which these groups are placed in the above table is arbitrary. No group gets any precedence over any other group to fix up the direction of numbering.They all obey the lowest set of locants rule. TYPE B : Functional groups which can only used as suffixes to form the parent compound. Name of the groupstructure AlkeneAlkyne*These groups(ene and yne) enjoy the same priority. Do not mistake their relative placement in the above table as priority order. The locants of enes  and  ynes  commonlyobey the lowest set of locants rule. If the sets of locants for enes  and  ynes  are samein the two opposite directions of numbering the principal chain, in that case only ene gets precedence over yne . Otherwise they enjoy the same priority and obey only thelowest set of locants(for ene and yne) rule.*When enes  and  ynes  are present in the longest carbon chain alongwith other functionalgroups(type-C), then enes and ynes appear as co-suffixes with the seniormost functionalgroup. Therefore such groups are used as suffixes only. This may not be mistakenfor alkenyl and alkynyl groups which are used as prefixes. All these will be madeclear very soon.    TYPE C : Functional Groups which can be used both as a suffix to form the parentcompound or prefix to form a substituent When a compound contains more than one functional groups belonging to type Cthen, the one having the highest priority(called the principal functional group) will be used assuffix to form the parent compound and all others  will be used as prefixes(i,e as substituents)of the parent compounds. Note that ene  and  yne  functions belonging to type B groups appear always as co-suffixes with the highest priority group in the parent name. This thing will beclarified with a lot of examples later. PRIORITY ORDER AMONG TYPE (C) FUNCTIONAL GROUPS The following table gives the relative priorities or precedences of type-C functionalgroups in decreasing order . The terms given in the prefix column are the names of thefunctional groups when they are used as substituents(prefixes) and the terms given in thesuffix column are the suffixes used with the root words to form the parent compounds. Name of group structureprefixsuffix carboxylic acid  COOH carboxy  -oic acid (carboxylic acid) sulfonic acid-SO 3 Hsulfosulfonic acid acid anhydride COO CO - -oic anhydrideester  COOR' alkoxycarbonyl  -oate(carboxylate) acid halide COX halocarbonyl -oyl halide(carbonyl halide) acid amide CO NH 2  aminocarbonyl  -amide(carboxamide) nitrile  C N cyano  -nitrile(carbonitrile) aldehyde COH oxo(formyl)-al(carbaldehyde) ketone CO oxo -onealcohol-OHhydroxy -olthiol-SHsulfanyl/mercapto -thiolamines-NH 2 /-NHR/-NR  2 amino -amine   Nomenclature of Organic Compounds  Note that the suffixes given within parentheses in the above table are used only whenthe carbon atom of the functional group is not included in the longest carbon chain. The usualsuffixes given are used when the carbon atoms of the groups are included in the longestchain. Formyl is used as prefix(substituent) when the carbon atom of -CHO group is excluded from the principal carbon chain. This will be made more clear soon. General rules for naming compounds containing more than 1 functional group: 1.The longest carbon chain giving the lowest locant to the highest priority group is found out first for determining the parent compound. The C-C double bond or triple bond is(are) accommodated in the longest chain(old rule). All other functional groupsappear as branches(prefixes) which are written first followed by the name of parentcompound. The ene  or  yne  appear as co-suffixes with the highest priority group. Example: CH 38765 Cl 4321 OOHOHOOCH 3 N 5-chloro-2-cyano-4-hydroxy-7-methoxy-6-oxooct-3-en-1-oic acid OR5-chloro-2-cyano-4-hydroxy-7-methoxy-6-oxooct- 3-enoic  acid In this molecule, there are 7 functional groups including the ene  function. The functionalgroup having highest priority(see above table) is carboxylic acid(-COOH). So the parentcompound is a carboxylic acid(oic acid), not alcohol(ol), nitrile or a ketone(-one). The carboxylcarbon is numbered 1 as per rule. All functional groups other than the highest prioritygroup(COOH) excepting the ene function are used as substituents and the names given inthe prefix column in the above table are used for naming these substituents.  Ene  is used asa co-suffix before the suffix of the principal functional group(oic acid). The locant of ene  and  oic acid   are placed before the respective suffixes(ene and oic acid). The last letter e  of en e is dropped as it cannot face a vowel in -  o ic acid  . The locant of oic acid(1) is usually notwritten. You can write the name of the parent compound as oct-3-en-1-oic acid or oct-3-enoic acid, the latter being the preferred name. Example: H 5 O 4321 OOOHOHClCH 3 ethyl 4-chloro-3-hydroxy-2-(hydroxymethyl)-5-oxopentanoate    In this molecule, there are four functional groups namely ester, two hydroxy and aldehydegroups. Since ester group has the highest priority among them, the parent compound is anester(alkanoate). The alkyl group of the alcohol part is written first as usual. This is followed  by the substituents of the longest alkanoate chain. The terminal aldehyde carbon(C-5) is a partof the main chain, so the prefix oxo is used(not formyl). At C-2, the branch is hydroxymethyland at C-3 the branch is hydroxy while at C-4 the branch is chloro. Since the first word ishydroxy in both the groups, the simple(or shorter) branch hydroxy is written first followed bythe complex(longer) branch hydroxymethyl.2.If the longest chain of equal lengths are available on two directions, then the oneassociated with greater number of functional groups is taken as the principal carbonchain for naming the parent. If the number of functional groups is same in both thechains, then the chain bearing the higher priority functional group is taken as thecorrect longest chain. 4321 OOHO H 5 OH  6 NH 2 6-amino-5-hydroxy-4-(2-oxoethyl)hexanoic acid In the above example -COOH is the principal functional group and so the parentcompound is alkanoic acid. Longest chain of six carbon atoms is available on both thedirections from C-4. The chain containing two functional groups(-OH and -NH 2 ) is taken asthe correct longest chain. Note that although the other chain bears a higher priority group(-CHO), still it is not considered as the principal chain for naming. The complex branch atC-4 is 2-oxoethyl because the terminal aldehyde group(C=O) is included in the main branchethyl and hence is prefixed by oxo(not formyl). The name formylmethyl can be used in placeof 2-oxoethyl but the latter is the preferred name of the group.  NH 2 OOH NH 2 65 4 321 2-amino-5-methyl-6-oxohex-3-ynamide 65 4 3 2 NH 21 OOHONH 2 OH 2,6-diamino-5-formyl-6-oxohex-3-ynoic acid In first case aldehyde carbon is included in the longest chain, not CH 3  carbon. Notethat the longest chain(C-6) is available in both the directions from C-5. The longest chainwhich has greater number of functional groups attached to it is taken as the correct longestchain. That is why aldehyde carbon was taken in the main chain and the suffix oxo is used for it, not formyl.    Note that when aldehyde group remains as a part of the longest chain, itwill be expressed by prefix  oxo . However if it remains outside the main chain, it will beexpressed by prefix  formyl  . Note thate  yne  has appeared as co-suffix with amide and the   Nomenclature of Organic Compounds last letter   e  of yne has been deleted as it cannot face a vowel in the word - a mide. The suffixof amide(1) has also been deleted.In the second case, between aldehyde and amide function the latter has greater  priority and so it is included in the principal chain, not aldehyde. For aldehyde, the prefixformyl is used as it is outside the principal chain. For the amide, both the term oxo for theC=O and amino for the NH 2  groups were used in alphabetical order. Note that when derivativesof carboxylic acids such as ester, amide and acid chloride are included in the main chain and those groups are not highest priority groups in the chain, the prefixes used for them are asfollows. functional groupprefixes used amideboth amino and oxo (not aminocarbonyl)acid chlorideboth chloro and oxo (not chlorocarbonyl)esterboth alkoxy and oxo (not alkoxycarbonyl) Example: OHOCl 65 4321 2-ethyl-4-formylhexanoyl chloride   OHOOCH 3 O 4321 4-methoxy-2-methyl-4-oxobutanoic acid  In the first case, aldehyde function has been excluded in the longest chain and the prefix formyl has been used for that. In the second case, since carboxylic acid has higher  priority over ester function, the parent becomes alkanoic acid. Since ester carbon is included in the main chain, two prefixes- methoxy and oxo have been used and arranged in alphabeticorder. OCH 3 OSO 3 H4-methoxy-3-methyl-4-oxobutane-2-sulfonic acid  4321 In this case, sulfonic acid has higher priority than ester, so the parent compound isalkanesulfonic acid. Since ester carbon is included in the longest chain, two prefixes namelymethoxy and oxo are used as explained before. Sulfonic acid group gets the lowest locant. Example: CH 3123 O 456 CH 37 OHBr Cl H 2  N OH3-aminopropan-1-ol(not 3-hydroxypropan-1-amin 123 4-bromo-2-chloro-6-hydroxyhept-5-en-3-one
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