Nomenclature of Organic Compounds Dr. S.S.Tripathy Nomenclature of Aliphatic/Acyclic compounds Line-Angle Formula (Skeletal Structure or Stick Figure) : Very handy for writing organic structures, mostly for cyclic compoounds. Carbon atoms are assumed to be present wherever two lines meet or a line begins or ends. N, O, X, S (heteroatoms) are shown while C, H are not shown. H is shown onto a heteroatom. NH O OH = H 3 C NH CH CH C H 3 C CH 3 CH 3 CH 3 CH C CH 3 O OH Alkanes Rule: Longest continuous carbon chain bearing maximum number of branches, numbered in the direction in which any alkyl branch is met first (Lowest Set of Locant Rules). Name of alkyl branches written first with alphabetic order followed by Word Root + ane(primary suffix). The first letter of the complex branch is considered for alphabetic ordering. For simple branch the multiplying prefixes di-, tri-, tetra- are not considered for alphabetic ordring. Complex branches are multiplied with the prefix bis, tris, tetrakis, pentakis etc. Locants are separated by commas and no space in between branches and parent alkane. If the set of locants is same from both side, then the alphabetically senior branch gets the lower locant. branches + alk + ane Examples: Lower Set of Locants Rule: H 3 C CH CH CH 2 CH 3 CH CH 3 CH 2 CH 2 CH 3 CH 2 CH 3 1 2 3 4 5 6 7 8 H 3 C CH CH CH 2 CH 3 CH CH 3 CH 2 CH 2 CH 3 CH 2 CH 3 1 2 3 4 5 6 7 8 4-ethyl-6,7-dimethyloctane(wrong) 5-ethyl-2,3-dimethyloctane(correct) H 3 C CH 2 CH CH CH 2 CH 2 CH 2 CH 2 CH CH 3 CH 3 CH 3 CH 3 1 2 4 3 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 3,4,9-trimethyldecane (wrong) (not lower set: begininng with 3) 2,7,8-trimethyldecane (correct) (Lower set: beginning with 2)
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Nomenclature of Aliphatic/Acyclic compounds2' 3' 6,6-bis(2,2-dimethylpropyl)dodecane A complex branch has to be multiplied with the prefixes bis, tris etc. (not di, tri etc.) Nomenclature
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Nomenclature of Organic Compounds
Dr. S.S.Tripathy
Nomenclature of Aliphatic/Acyclic compounds
Line-Angle Formula (Skeletal Structure or Stick Figure):Very handy for writing organic structures, mostly for cyclic compoounds. Carbon atoms are assumed to bepresent wherever two lines meet or a line begins or ends. N, O, X, S (heteroatoms) are shown while C, H arenot shown. H is shown onto a heteroatom.
NH
O
OH
= H3C
NH
CH
CH
CH3C
CH3
CH3
CH3
CH
C
CH3
O
OH
AlkanesRule: Longest continuous carbon chain bearing maximum number of branches, numbered in the direction
in which any alkyl branch is met first (Lowest Set of Locant Rules). Name of alkyl branches written first withalphabetic order followed by Word Root + ane(primary suffix). The first letter of the complex branch isconsidered for alphabetic ordering. For simple branch the multiplying prefixes di-, tri-, tetra- are not consideredfor alphabetic ordring. Complex branches are multiplied with the prefix bis, tris, tetrakis, pentakis etc. Locantsare separated by commas and no space in between branches and parent alkane. If the set of locants is samefrom both side, then the alphabetically senior branch gets the lower locant.
branches + alk + aneExamples:Lower Set of Locants Rule:
Naming a complex branch:Latest Rule: Numbering made from one terminal to the other giving lower locant to -yl. When locant of -yl is 1,then the suffix ‘ane’ is replaced by ‘yl’ and the loacnt 1 is dropped. For example, propyl, butyl, etc instead ofprop-1-yl, but-1-yl.Simple alkyl groups like methyl, ethyl, propyl, butyl in which the locant of -yl is 1 are called simple branches.All other alkyl branches containing subbranches of simple alkyl groups like 2-methylpropyl or having locant of-yl other than 1 like propan-2-yl etc. are considered as complex branches. The first letter of the complexbranches is considered for alphabetic numbering which includes di-, tri-etc. Such branches are multiplied bythe prefixes bis, tris, tetrakis etc.When locant of ‘yl’ is not 1, then letter ‘e’ of ‘ane’ is replaced by ‘yl’,with the locant of ‘yl’ prefixing it. Forexample propan-2-yl etc.
3
CH3 CH
CH3
propan-2-yl
CH3 CH2 CH2
propyl
2
1
3 2 1
CH3 CH2 CH
CH3
4 3 2
1
butan-2-yl
CH3 CH2 CH2 CH2
butyl
34 2 1
CH3 C
CH3
CH3
32
1
2-methylpropan-2-yl
CH3 CH
CH3
CH2
3 2 1
2-methylpropyl
CH3 C
CH3
CH3
CH2
32 1
2,2-dimethylpropyl
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
Old Rule:The carbon atom of the alkyl branch directly bonded to the principal carbon chain is numbered 1’ to find thelongest chain. Ultimately prime over the locant is dropped once it is put insidie parenthesis.
2-methylpropyl and 2,2-dimethylpropyl remain the same for both old and new conventions.
N.B: Many text books still use the old convention of naming a complex alkyl branch(1,1-dimethylethyl). Thenames like isobutyl, isopropyl, sec-butyl, tert-butyl, neopentyl are also used in some texts in IUPAC naming.So the student should not take much critically on this aspect. Remember that a structure can have more thanone IUPAC names out of which one is PIN(Preferred IUPAC Name) as per the latest conventions but onename can have a unique structure.Two branches having same initial words:When two groups have same initial words(or letters), the longer branch gets the higher locant. Beween
methyl and methylpropyl the former gets a lower locant.
If you write according to old system, then for complex branch the prefixes di-, tri- are considered for alphabeticordering as in the new convention. Using the common names of the alkyl groups, the prefix tert- and sec- are notconsidered while the prefixes iso and neo are considered for alphabetic ordering.
3
42
1 5 6 7 8
9
10
11
12
3'
2'
1'
1'
2'
3'
6,6-bis(2,2-dimethylpropyl)dodecane
A complex branch has to be multiplied with the prefixes bis, tris etc. (not di, tri etc.)
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
SHORT REPRESENTATIONS OF SOME COMMON ALKYL GROUPS:The following abbreviations are used for the alkyl groups written against their names.
methyl Me isobutyl i-Buethyl Et sec-butyl s-Bun-propyl n-Pr tert-butyl t-Buisopropyl i-Pr n-butyl n-Bu
SAQ I.4: Give the IUPAC names of the following compounds shown in line drawings.
(i) (ii)
(iii) (iv)
(v) (vi)
(vii) (viii)
(Rule for naming compound (viii): When two or more longest chains containing same number of branchesand same set of locants for the branches compete with each other, IUPAC recommends that thelongest chain which contains greatest number of carbon atoms in the branches is correct.
(ix) (ix) (x)
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
(xi) (xii)
(xiii)
SAQ I.5: Draw the line structures for the following molecules.
(i) 5-(2-methylpropy)dodecane (ii) 4-(propan-2-yl)-4-propylnonane(iii) 5-(butan-2-yl)-5-(propan-2-yl)decane (iv) 4,4-bis-(2-methylpropan-2-yl)heptane(v) 3-ethyl-6-(5-methylhexan-3-yl)-8-(propan-2-yl)undecane
3,3,4-trimethylpentane(wrong); the set of locants =3,3,4 which is higher
2,3,3-tripmethylpentane(correct) , The set of locants 2,3,3 is lower and is correct..
(iv) 3 5
6
71
2
4CH2
CH
CH2
CH
CH
H3CCH3
H3CCH3
CH2
CH3
(correct); 3 5
67
12
4CH2
CH
CH2
CH
CH
H3CCH3
H3CCH3
CH2
CH3
(wrong)
The second one is violating the branching rule. In the first, there are more number of branches attachedto the main chain. Count for yourself to verify.
Name: 3-ethyl-2,5-dimethylheptane.
The reverse direction of numbering would have given a higher set of locants: 5-ethyl-3,6-dimethylheptanewhich is wrong.
(v)
1 2 3
H3C C
CH3
CH3
CH3
; 2,2-dimethylpropane (same name if we reverse the numbering)
(vi)
1 2 3 4
H3C C C CH3
CH3
CH3
CH3
CH3
; 2,2,3,3-tetramethylbutane(same name on reverse numbering)
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
(vii) CH39
8
7
6
5
4
3
2
CH31
CH3
CH3
; 5-methyl-4-propylnonane (reverse numbering would have given the
set of locants 5,6 which is higher)
(viii) 5-ethyl-6,7-dimethyl-4-propyldecane
(The set of locants are same on either side. Hence lowest locant is given to alphabetically seniormost branchethyl by numbering from left to right).
SAQ.I. 2: While writing the structure of a compound from its name, first look to the word root of the parentalkane. In this case it is alk(e.g pent-, hex-, but- etc.). First draw a carbon chain containing the requirednumber of carbon atoms in straight chain. Let us take the first bit.
(i) The parent alkane is pentane. So let us first draw: C-C-C-C-C. Then number them from one end to theother end. Attach the substituents(branches) at the appropriate carbon atoms.
C C C C C
CH3 CH3
1 2 3 4 5
Then attach the required number of hydrogen atoms to each carbon atom of the main chain bearing inmind that the valency of carbon is 4.
(ii) 3-ethyl-8-methyldec-5-yne(ethyl gets precedence over methyl due to alphabetical seniority ofthe former)
NEW:
Longest continuous carbon chain to be taken as parent hydrocarbon. This may or may not include C C /
C C . If C C / C C is not included, the parent becomes alkane. In such case, the branch containing
C C / C C are written along with other alkyl branch in alphabetic order.
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
Naming branch containing C C / C C :Monvalent alkenyl and alkynyl group:The letter ‘e’ of ene/yne is replaced by ‘yl’. It becomes alkenyl or alkynyl. Note that ‘en/yn’ has its locant and‘yl’ also has its locant. If the locant of ‘yl’ is 1, then it is dropped. According to new convention, the branch isnumbered from one terminal to another like a complex alkyl group. However, the old rule is still followed by sometext books in that the carbon atom bonded to the longest chain is numbered 1. See the following examples.
1
prop-1-en-1-yl
3 2 1
CH3 CH CHprop-2-en-1-yl or allyl
3 12CH2 CH CH2
ethenyl or vinylCH2 CH
or prop-2-enyl or prop-1-enyl
CH3 C
CH2
3 2
1
prop-1-en-2-yl
CH3 CH CH CH
CH3
5 4 3 2
1
but-3-en-2-yl
(1-methylethenyl) (1-methylbut-2-enyl)
HC C HC C CH2 H3C C C
ethynyl prop-2-yn-1-ylor prop-2-ynyl
prop-1-yn-1-ylor prop-1-ynyl
Bivalent alkylidene group:If =C- is directly bonded to the longest chain, then the group is bivalent. In that case, a suffix ‘idene’ is to beused with the respective ‘alkyl’ group.
alkyl + idene = alkylidenealkyl - alkylidene
CH3- (methyl group) CH
2= (methylidene group)
CH3-CH
2-(ethyl) CH
3CH= (ethylidene)
CH3-CH
2-CH
2-(propyl) CH
3-CH
2-CH= (propylidene)
H3C
CH
H3C(propan-2-yl/isopropyl
H3C
C
H3C(propan-2-ylidene/isopropylidene)
Naming bivalent group contianing one more C C / C C :
2-methyl-7-methylidenenonane(new name) 5-(prop-2-ynyl)nonane( new name)2-ethyl-7-methyloct-1-ene(old name) 4-butyloct-1-yne(old name)
SAQ : Write the names of names of the following alkenes and alkynes on the basis of the new rules.Compare the names with those obtained by using old rules.
(i) CH3
CH3
CH3
CH3
CH3
(ii)CH3
CH3
CH3
CH3
CH3
CH3
(iii)
CH3
CH3
CH3CH
Answer:(i) 3,4-diethyl-5-methylhept-2-ene(same according both the rules as the C=C bond is included in
the longest chain)
(ii) 4-ethyl-2,7-dimethyl-5-propylidenenonane(new);
Haloalkanes(Alkyl Halides)Rule:The halo group(-X) may or may not be directly bonded to the longest carbon chain. If it is not directly bonded,then it is part of a complex alkyl group with a halo subbranch. The naming is done just like any alkane. Halobearing group competes with other alkyl groups for alphabetical seniority.
1. If there will be at least one C=C or C C , then primary suffix ‘ane’ is not used. In stead ‘ene’ or
‘yne’ is used. If there are more than one C=C or C C , then di-, tri- etc. are used as prefix to ‘ene’, ‘yne’.
In such case, the letter ‘a’ is suffixed to the Word Root (alk) to maka it alka (eg buta, penta, hexa etc.). Forexample buta-1,3-diene(not but-1,3-diene).
2. C=C or C C can be used as primary suffix as ‘ene’ or ‘yne’ along with the secondary suffix of the
seniormost functional groups. They can also be used in a branch with the name alkenyl, alkynyl, alkylidene,alkenylidene or alkynylidene etc.3. The following table gives the functional groups with decreasing priority order for which secondary suffixis used. These are called Type C groups which can both be used as suffix or as prefix(branches).
Type C functional Groups:Name of group structure prefix suffix
Deletion of ‘e’: If the secondary suffix begins with any vowel such as ‘a, y, i, o, u’ then the letter ‘e’ tobe deleted from prmary suffix ane/ene/yne. For example butanol, pentanone, but pentanenitrile.
(NB: For acquainting with the IUPAC naming compounds containing single functional group,please refer e-Concepts in Chemistry for Junior Level: Nomenclature Chapter-II)
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
Rules:
* The LONGEST carbon chain bearing the highest priority functional (type C) group should also bearmaximum number of other type C groups. Such group(s) cannot be ignored or be excluded from the longest
chain. Such a chain may exclude C=C or C C if required, if they are not part of the LONGEST chain
containing maximum number of type C groups.
Conclusion: The longest chain bearing the highest priority group may or may not include other functional
groups or C=C/ C C . Betwen any typc C group and C=C/ C C , the former is preferred.
* The one having highest priority among such groups will make the secondary suffix. In other wordsthe parent compound will be named after this. Other such groups will be used as branches(prefixes). For-OH it is hydroxy, for (-C=O) it is oxo and so one. Look to the prefix column for this. The suffix nameswhich are written inside parenthesis below their respective first names are used only when such functionalgroup is outside the principal carbon chain. For example, if -COOH remains within the principal chain, i.ethe carboxyl carbon is counted as no. 1, then the secondary suffix ‘oic acid’ is used. If -COOH remainsoutside the carbon chain, then ‘carboxylic acid’ is used. As a prefix also if -CHO(aldehyde) group remainsoutside the carbon chain, then ‘formyl’ is used otherwise ‘oxo’ is used.
Groups which are used only as substitutents(Prefix): Type A groups
Such groups do not have any priority order. All such groups obey LSL rule.
Name of the group General formulaalkyl R-alkoxy RO-alkylsulfanyl(alkylthio) RS-halo X-nitro NO
2-
alkenyl R CH CH
alkynyl R C C
phenyl C6H
5-
cycloalkyl cyclopropyl, cyclobutyl etc.
(Note that C=C and C C are called Type B functional groups which are used as primary suffix(ene/yne)
* Since -COOH and derivatives of -COOH and -CHO are terminal functional groups, the one whichhas the highest priority among them always gets no. 1 locant.* When –CN is a lower priority group in a molecule, it is never taken inside the principal carbon chain.It is always used as prifix(cyano). Cyanide carbon is never counted in such case.
* In polyene/enynes C=C and C C enjoy the same priority. However in case of tally, ‘ene’ gets
the precedence.
CH38
7
6
5
Cl
4
3
2
1
O
OH
OHO
O
CH3
N
5-chloro-2-cyano-4-hydroxy-7-methoxy-6-oxooct-3-en-1-oic acid OR
(note that for aldehyde group, we used the prefix ‘oxo’ as it is a part of the carbon chain. For ketones toowe shall use ‘oxo’.
4
3
2
1
O
OH
O H
5
OH 6
NH2
6-amino-5-hydroxy-4-(2-oxoethyl)hexanoic acid
The longest chain containing more number of functional groups is chosen irrespective their priorities.
NH2
OOH
NH2
65 4 3 2
1
2-amino-5-methyl-6-oxohex-3-ynamide
6
5 4 3 2
NH2
1
O
OHO
NH2
O
H
2,6-diamino-5-formyl-6-oxohex-3-ynoic acid
In the 2nd case above, amide is senior to aldehyde, hence amide carbon was included in the principal chain.Since -CHO is now excluded from main chain, the prefix ‘formyl’ has been used. Note that for amide group,we used two suffixes, one for -C=O(oxo) and other other for -NH
2(amino).
functional group two prefixes usedamide both amino and oxo (not aminocarbonyl)acid chloride both chloro and oxo (not chlorocarbonyl)ester both alkoxy and oxo (not alkoxycarbonyl)
Compounds containg idential functional groups:In such case, the secondary suffix is prefixed with di-, tri- etc. For example, diol, trione, dial etc. In such casethe ‘e’ of primary suffix is not dropped.Rule: The principal chain should bear maximum number functional groups.
Compound containing 3 or more identical carbon-bearing terminal functional groups :Case-I If the 3rd group is directly bonded to the principal chain containing two groups, then all the three arenot included for the parent carbon chain. In such case, the following suffixes are used after alkane.
Case-II: If the 3rd group is not directly bonded to the carbon chain, then two groups in the chain are includedin the principal chain, the third becomes subbranch of an alkyl branch eg. carboxymethyl, amioncarcarbonylmethyletc.
(When two alkoxy(OR’) parts of diester are different, each alkyl group is prefixed with the locant of carboxylcarbon to which the alkoxy group is attached)
Divalent radicals using the suffix ‘idene’ has been already discussed. That is case when one H atom is removedfrom a monovalent alkyl group. Similarly when two H atoms are removed from a monovalent alkyl group, itbecomes a trivalent radical.Trivalent radical: yl of alkyl is suffixed with ‘idyne’.
Note that these radicals cannot attach with any carbon chain. However such groups are used in complexcompounds of metals ions as ligands.Bivalent radicals obtained by removing H atom from the two terminal carbon atoms(two monovalent radicalsin one species) of a normal alkane(unbranched)
The suffix ‘ene’ is used after polymethyl : polymethyl+ene = polymethylene
CH2
CH2 tetramethyl+ene = tetramethylene (butylene)
–CH2–CH
2– : ethyl + ene = ethylene
Similarly hexamethylene, pentamethylene etc. These namings are used in trivial systems, eg.(1) hexamethylene diamine(for hexane-1,6-diamine) (2) ethylene dichloride(1,2-dichloroethane)Multivalent radicals on two terminals :
alkane + diyl + idene (if both the terminals are C=)
alkane + diyl + idyne (if both terminasl are C )
alkan+yl+ylidene (if one is C– and other is C=)
CHCH
butane+diyl+idene = butanediylidene
CHCH
butane + diyl + idyne = butanediylidyne
CHCH
butan-1-yl-4-ylidene
Such groups(restricted to divalent on either side) can be used in naming compounds in trivial system egbutanediylidene diimine. However trivalent radicals on either side cannot be used often usually in organicstructures.
* If the cyclic ring is attached to one carbon atom or one functional group, then the naming should bedone as a cyclic compound. In other words, if the higher priority functional group is directly attached to thering, then it is named as a cyclic compound.* If the cyclic ring is attached to more than one carbon, then it can have two alternative names : (i) as analiphatic compound with cycloalkyl prefix or (ii) a cyclic compound with aliphatic prefix. The aliphatic name ispreferred(PIN)j in such case. See the following examples.
Only in case of the 1st compound, the cyclic name is preferred. In all the other three examples, the aliphaticnames are preferred as the functional group is not directly bonded to the ring.
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
Other logic for naming as valid for aliphatic compounds are also valid for ring compounds. After the highestpriority group, C=C is considered(not other functional group) for LSL rule.
6): It is primarily the hybrid of the two resonating structures.(Refer Chemical Bond for details).
Benzene and its derivatives are aromatic compounds. Such compounds are unique in their behaviour. Theyare more stable and hence less reactive than their acyclic analogue hexa-1,3,5-triene apart from havingacceptable fragrance(aroma). The details of aromaticity will be discussed later in the chapter aromatichydrocarbons.
Answer: (i) (chloromethyl)benzene(Cl is not a functional group) (ii) 1-phenylmethanamine(iii) methyl 2-phenylacetate(ethanoate) (iv) phenylacetonitrile(phenylethanenitrile)(v) 2,3-dimethyl-3-phenylbutanal
Disubstituted Benzene :
X
Y
X
Y
X
Y
12
11
2 2
3 3
43
4
5 55
6 6 6
4
1,2- or ortho 1,3- or meta 1,4- or para
There are three isomers for two substituents namely (i) ortho(1,2) (ii) meta(1,3) (iii) para(1,4). There twoequivalent ortho positions with resepct to a particular substitutent on either side of it. Similarly there are twoequivalent meta positions for group. But there is only one para position.
Naming:
Rules: Priority order among Type C groups are the same as for aliphatic compounds.
-COOH >-SO3H > -COOR’ > COCl > CONH
2 > -CN > -CHO > -COR > -OH > -NH
2
(I) If the comounds has both or at least one Typce C group, then the parent compound is given after thehigher priority group, the other one appears as branches(prefixes) see these examples.
N,N-dimethyl-4-nitroaniline 3-acetylbenzenesulfonic acid 2-hydroxyacetophenone(II) If both groups belong to type A (not type C), then the alphabetic senior group will get the lower locant.
CH3
1-ethenyl-3-methylbenzene(PIN(3-ethenyltoluene)
CH3
NO2
1
4
1-methyl-4-nitrobenzenOr, 4-nitrotoluene
CH3
Cl1
2
1-chloro-2-methylbenzene(PIN(2-chlorotoluene)
OCH3
CH2CH3
1
4
1-ethyl-4-methoxybenzene(PIN(4-ethylanisole)
1
2
HO
H2N 2-(4-aminophenyl)phenol
* If aromatic and aliphatic parts contain type C group, then the part bearing higher priority functionalgroup gives the parent name. If idential functional group present in both the parts, then it will be named asaromatic.
Tri or polysubstituted benzene:1. If one of the groups belongs to type C, then the name is given after that groups getting locant 1. If morethan one of such groups are there, then the highest priority groups determines the name of the compound.
2. If all the groups belong to type A, then LSL rule determines the name. See these examples.
Compounds containing more than one benzene ring fused at the ortho or 1,2 positons are called polynuclearor condensed aromatic compounds. A few examples are given below.
or
1
2
3
45
6
7
8
1
2
3
45
6
7
8
10
(napthalene)
or
1
23
45
6
7
8 9
98
7
6
5 4
32
110
(anthracene)
Then tetracenene(four benzene rings fused linearly), pentacene and so on.Monosubstituted naphthalene:For monosubstituted naphthalene, there are two non-equivalent positions namely 1-(α) or 2-(β).
1
22
22
1
11
Di- or polysubstituted naphthalene:For such compounds the numbering of carbon atoms is shown before. The highest priority functional groupto get the lower locant.
Anthracene:For monosubstitued anthracene has 3 non-equivalent position, 1, 2 and 9. But for di- and polysubstitutedanthracene, the numbering has been given before.
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
11
11
2
2
2
2
9
9
COOHOH
anthrancene-2-carboxylic acid anthracen-9-ol
12 CHO
CH3
45
OH
CH3
NO2
12
45
7
6
9
5-methylanthracene-2-carbaldehyde 4-methyl-2-nitroanthracen-9-olHeteroaromatics and Heterocyclics:
Bicyclic Compounds:A bicyclic compound is one which can be converted to an open chain acyclic compound by making
cleavage(scission or breakage) of covalent bonds two times.
1st cleavage 2nd cleavage
open chain
bridgehead carbon
bridgehead carbon
bridges
There are two bridge head carbon atoms and three bridges. The bridge may contain only a single covalentbond(no carbon atom).
bicylo[x.y.z]alkanex, y and z are ring size i.e number of carbon atoms in three bridges from highest to lowest bridges. Thisexcludes the two bridgehead carbon atoms. If a bridge has no carbon atom(only a covalent bond) then it willget the numeral ‘0’.alkane will be from (x+y+z) +2 i.e all the carbon atoms. The numbering will start from one bridgeheadthrough the longest bridge to the other bridgehead, then to bridge of intermediate length and shortest bridge.For naming a branched bicyclic compound, the priority order of functional group and LSL to be taken intoaccount.
1
2
3
4
5
67
8
9
10
bicyclo[4.3.1]decane
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
bicyclo[2.2.0]hexane bicyclo[5.3.1]undecane
532 12
0
bicyclo[1.1.0]butane
1 10
5 4
6 1
3
2
CH3
5-methylbicyclo[2.2.0]hex-2-ene
2 1
3
4
5 6
7
11
10
8
9
CH3
3-methylbicyclo[5.3.1]undec-8-ene
CH 3
23
4
5
6
78
9
1
10
6-methylb icyclo[5 .2.1]dec-3-ene
OC H3
O 2N
HO
2
1
4 5
6
7
8
3
9
4- methoxy-2-nitrobicyclo[3.2.2]nonan-6-ol
SAQ:SAQ III.14:Write the names of the following bicyclics.
The compounds in which two rings share one common carbon atom are called spirocompounds.
spiro[x.y]alkane
x and y are chain lengths in the two rings or the number of carbon atoms in the two rings which link to thecommon atom(called spiro atom), which are separted by full stop. Note that the spiro atom is excluded inthese numbers. The numbers are written in increasing order eg. [4.5] unlike that followed in bicycliccompounds(decreasing order). While naming the parent alkane the total number of carbon atoms in thecompound is counted.
4
3
2
1
5
6 7
8
10 9
spiro[4.5]decane
The numbering starts in the smaller size ring from the carbon atom adjacent to the spiro atom andproceeds around the smaller ring back to spiro atom and then proceeds around the second ring(largersize ring). While going from the smaller ring towards the larger ring the lowest set of locants rule iskept in mind. If there is a C=C, then ene should get the lower locant compared to alkyl or other typeA groups.
2
1
3
4 5
8 7
6
CH3
8-methylspiro[2.5]oct-4-ene
9
8
7
65
4
1 0
3
1
2
CH 3
1 -e thy lsp iro [3 .6 ]dec-6-ene
8
7
9
6
5
4
1
3
2
spiro[4.4]nona-2,7-diene
SAQ III.15: Name the following spiro compounds.
(i)
CH3
CH3
(ii)- CH3
CH3
(iii)
C H 3
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
(iv) Cl (v)
CH 3
Answer:(i) 1,4-dimethylspiro[2.7]deca-5,8-diene (ii) 6-isopropylspiro[3.5]non-1-ene(iii) 4-methylspiro[2.2]pent-1-ene (iv)1-chloro-5-ethylspiro[3.3]heptane(v) 4-methylspiro[4.8]trideca-1,7,9-triene
1. Substituted oxirane: The O atom of oxirane is always numbered 1. Alphabetical seniority of alkyl groupsdecides the correct direction of numbering. These are also named as epoxyalkanes, the locants of the epoxyare to be prefixed to it.
H 3C CH CH CH 2 CH 3
O
(2 ,3 -ep ox yp en tan e)
1
23
2 -e th yl-3 -m eth ylox iran e
2. Imines: =NH is called imine group. It is a bivalent group. The name of imine is alkan-x-imine where x is thelocant of imine.
H 3C CH 2 CH 2 CH NH
bu tan -1 -im ine
H 3C CH 3
NHprop an-2 -im in e
3. Lactones: Cyclic esters are called lactones. Butyrolactone, valerolactone, caprolactone are a few examplesof lactones.
H 2C
H 2C
H 2C C
O
OH 2C
CH 2
H 2C C
O
CH 2
O
H 2C
CH 2
H 2CC
O
CH 2
CH 2
O
-bu tyrolactone -valerolactone -caprolacton e
4. Lactams: Cyclic amides are called lactams. Butyrolactam, valerolactam, caprolactam are few examples oflactams.
H 2C
H 2C
H 2C C
O
NHH 2C
CH 2
H 2C C
O
CH 2
NH
H 2C
CH 2
H 2CC
O
CH 2
CH 2
NH
-butyrolactam -valero lactam -caprolactam
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
5. Ketenes: R-CH=C=O are called ketenes. Such compounds are named according to IUPAC rule.Example: CH
3-CH=C=O prop-1-en-1-one
6. Imides: Imides contain -CO-NH-CO- group. It is analogous to acid anhydride except -O-in anhydrideis replaced by -NH- in imide. They are named according to IUPAC rules.
CH3-CO-NH-CO-CH
3N-acetylacetamide.
ALTERNATIVE NAMING PROCEDURE FOR ETHERS AND 20 AMINES
Ethers:(OXA System)
1. Oxygen atom in ether is treated like a carbon atom in finding out the longest continuous chainincluding the oxygen atom. In otherwords, the oxygen atom is counted like a carbon atom in determiningthe the name of parent alkane. The ether group(oxygen atom) is indicated by the prefix oxa withits locant placed before it. Lowest set of locants rule is followed while choosing the direction ofnumbering. Note that ether group (O atom) does not enjoy any priority as functional group.
CH36
5
O4
3
2
CH31
CH3
(2-methyl-4-oxahexane)
Note that IUPAC does not have a fixed procedure for naming ethers, although the one discussedbefore(alkoxyalkane) is the preferred name. The oxaalkane procedure of naming ether is simpler,although used to a lesser degree of preference.
Cyclic ethers:When oxygen atom remains as a part of a ring, it is a cyclic ether. The systematic names of these ethers
and their alternative names according to oxa system are given below.
Note that oxirane is also commonly called ethylene oxide or epoxyethane.
Sec-amines (AZA System)
Like oxygen atom in ether, the nitrogen atom in a sec-amino group( NH) is counted like a carbon atomin finding out the longest continuous chain. The prefix aza is used for the amino function with its locant beforeit.
(a) n-alkyl : straight chain : example n-propyl, n-butyl, n-pentyl etc. ( n = normal)
CH3 CH2 CH2 CH3 CH2 CH2 CH2
n-propyl n-butyl
(b) sec-alkyl: derived from a 20 carbon atom. The carbon bearing the unsatistfied valency has one H atom.
CH3 CH2 CH CH3 CH3 CH2 CH CH2 CH3
sec-butyl sec-pentyl
CH3 CH2 CH2 CH CH3
sec-pentyl
There is only one sec-butyl and hence can be used in naming. But there are two sec-pentyl groups, hence cannotbe used for naming. Can you say how many sec-hexyl group you can have from hexane ? Again two. You willget clear picture about this in the chapter ‘Isomerism’.
(c) tert-alkyl: derived from a 30 carbon atom. The carbon bearing the unsatisfied valency has NO H atom in it.
CH3 C
CH3
CH3
CH3 C
CH3
CH2CH3
tert-butyl tert-pentyl
Since there is one from each of the above, they can be used in naming.
Nomenclature of Organic Compounds
Dr. S.S.Tripathy
(d) isoalkyl group: contain -CH3 branch at the 2nd position.
CH3 CH
CH3
CH3 CH
CH3
CH2 CH3 CH
CH3
CH2 CH2
isopropyl(sec-propyl) isobutyl isopentyl
Note that isopropy is also sec-propyl as it satisfies both the definitions. But isopropyl is preferred.
(d) neopentyl group:
CH3 C
CH3
CH3
CH2 (neopentyl)
Naming by Common System(traditional or trivial system):