iupac nomenclature
TRANSCRIPT
IUPAC Nomenclature
IUPAC nomenclature uses the longest continuous chain of carbon atoms to determine the basic root name of the compound.The root name is then modified due to the presence of different functional groups which replace hydrogen or carbon atoms in the parent sturcture.
There are a number of different ways to modify the root name to indicate the functional groups present.
Substitutive : (most common) : the highest priority functional group modifies the suffix of the root name, while all other groups, or substituents, are added as prefixes to the root name.
Functional group : names the compound based on the highest priority functional group, i.e. as an alcohol, ketone, alkyl halide, etc.
Replacement : used to indicate when an atom, usually carbon, is replaced by another atom.
Conjunctive : used to combine named subunits (i.e. cyclohexanecarboxylic acid).
Common or trivial : due to widespread use, some compunds with simple names have been adopted into basic IUPAC nomenclature.
Remember: that organic molecules can in general be either chains (also known as acyclic)
or cyclic or a combination of both. In most cases this doesn't make a difference. The general rules for cyclic systems will be developed for cycloalkanes and can be applied to other scenarios.
molecules are not restricted to a single functional group, they can have several functional groups. A common example are amino acids which have both an amine and a carboxylic acid present.
Basic rules
The IUPAC systematic name of an organic compound can be constructed based on a series of steps and rules:
Indentification of the principle functional group and substituents Indentification of the longest continuous chain containing the principle
functional group.
Assign locants (i.e. numbering) to the principle functional group and substituents.
The steps and rules are summarised below, more details are provided as the cases are encountered.
Principle Functional group
The principle functional group is used to define the class the compound belongs to e.g. an alcohol, ROH
The principle functional group is usually given the lowest locant possible.
Longest chain The longest continuous chain containing the principle functional group defines the root name.
Other groups attached to this chain are called substituents.
If there are two chains of equal length, then the choice that gives the simplest substituents is chosen.
Numbering (i.e. assigning locants)
The numbers that define the positions of the principle functional group and substituents are called locants.
Compounds are numbered from one end of the longest continuous chain.
The locants are assigned such that the principle functional group gets the lowest possible locant.
If this results in a "tie" then the first point of difference rule is applied so that the first time a difference in numbering occurs, then the method that gives the lower number at this first difference is used.
In the event that there is no first point of difference then alphabetisation is used.
Basic IUPAC Organic Nomenclature
What's in a name?
The IUPAC name of an organic molecule is assembled from components that describe various features of the molecule.
Functional group suffixThis is added to the end of the name based on the principle functional group.
RootThis defines the number of atoms (usually carbon atoms) in the longest continuous chain that contains the principle functional group.
Substituent prefixAny groups other than the principle functional group are substituents and are added to the beginning of the name in alphabetical order.
MultiplierIf a group occurs more than once, a simple multiplier (e.g. di, tri, tetra, etc.) is used
to indicate how many times it occurs.
LocantsLocants are numbers (or occasionally letters e.g. N-) that define the position of the principle functional group and substituents. Typically there needs to be a locant for each functional groups and each substituent. Llocant for the principle functional group is placed before the functional group suffix, e.g. pentan-2-ol, see below.
The basic structure of the IUPAC name is shown schematically below :
Root names
C1 = meth- C2 = eth-
C3 = prop-
C4 = but-
C5 = pent-
C6 = hex-
C7 = hept-
C8 = oct-
C9 = non-
C10 = dec-
C11 = undec-
C12 = dodec-
C16 = hexadec-
C18 = octadec-
C20 = icos-
Functional Groups—Functional group is part of molecule which mainly responsible for its physical and chemical properties.
Some compound and their functional groups:
Table-1
S.N. General form of compounds Functional Group1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R-X
R-F
-X halo
16
17
18
19
20
21
22
23
Table2
Name of some important functional groups as prefix and suffix
Group Formula Prefix Suffix
Table-3
Important functional groups arranged in decreasing priority order for a nomenclature perspective
1
2
3
4
5
6
7
8
9
Principle functional group Secondary suffix
-OH ol
-CHO al/ carbaldehyde
-COOH oic acid/Caboxylic acid
-COOR oate/carboxylate
-CONH2 amide/carboxamide
-COO- oate/carboxylate
-RSH thiol
Group Common name
Alkanes
Nomenclature Formula
Functional group suffix = -ane
Substituent name = alkyl
.Simple alkane chains without branches are named using the appropriate root name plus the suffix -ane:
Propane
CH3CH2CH3
Simple cyclic alkanes without branches are named using the prefix cyclo plus the appropriate root name plus the suffix -ane:
Cyclopropane
Simple Branched Alkanes
The substituent is named in a similar way to the parent alkane. It is named based on the number of carbon atoms in the branch plus the suffix -yl.
CH3- methyl
CH3CH2- ethyl
CH3CH2CH2- propyl
CH3CH2CH2CH2- butyl
CH3CH2CH2CH2CH2- pentyl
2-methylpentane
CH3CH2CH2CH(CH3)2
3-ethylpentane
CH3CH2CH(CH2CH3)CH2CH3
3,3-dimethylhexane
CH3CH2C(CH3)2CH2CH2CH3
2,3-dimethylhexane
(CH3)2CHCH(CH3)CH2CH2CH3
4-ethyl-2-methylhexane
(CH3CH2)2CHCH2CH(CH3)2
Common names for alkyl substituents
Certain alkyl substituents are very common, and you should be able to recognise and name them quickly, these are listed below
Notes:
the the prefix "iso" is not hyphenated. the prefix "n-"denotes the straight chain substituent i.e. n-hexyl =
CH3CH2CH2CH2CH2CH2-
the symbol "R" is commonly used to generically represent an alkyl group, e.g. R-X
Structural formula
Name Generic line drawing
CH3- methyl-
CH3CH2- ethyl-
CH3CH2CH2-propyl-orn-propyl
(CH3)2CH- isopropyl-
CH3CH2CH2CH2-butyl-orn-butyl
CH3CHCH2CH3sec-butyl- or s-butyl
(CH3)2CHCH2- isobutyl
(CH3)3C-tert-butyl or t-butyl
Complex names for alkyl substituents
For the substituent: determine the point of attachment to the chain that defines the parent root (i.e.
the longest continuous chain) the first carbon in the substituent is regarded as the C1 of the substituent
from C1, find the longest continuous chain originating from C1 - this is the root for the substituent.
identify any substituents off this chain
list these alphabetically with appropriate multipliers
insert locants as required remembering that the point of attachment is defined as C1.
Now include this "complex" substituent in the overall name... the complex substituent appears in brackets proceeded by its locant the complex substituent is alphabetised based on the first letter of the name in
the bracket : this includes the multiplier e.g. di
this is because the term in brackets is the name of the whole complex substituent and not several substituents.
See Complex substituent name : 1,1-dimethylethyl
4-(1,1-dimethylethyl)-5-ethylnonane
Common alkyl substituents can also be named in this more systematic way.
Alkyl group, R- Common name Complex name (if different)
CH3- methyl-
CH3CH2- ethyl-
CH3CH2CH2- propyl-
(CH3)2CH- isopropyl- (1-methylethyl)-
CH3CH2CH2CH2- butyl-
CH3CH2CHCH3 sec-butyl- or s-butyl (1-methylpropyl)-
(CH3)2CHCH2- isobutyl (2-methylpropyl)-
(CH3)3C- tert-butyl or t-butyl (1,1-dimethylethyl)-
Remember that if a structure has two chains of equal length, then the choice that gives the simplest branches is chosen,
3-ethyl-2,4-dimethylhexane
Substituted Cycloalkanes
In principle, a substituted cycloalkane could be name in two ways, either as an alkyl substituted cycloalkane, or as a cycloalkyl substituted alkane
When the ring size (e.g. number of C atoms) is larger than the longest continuous chain, then the ring becomes the parent and hence the system is treated as a alkyl cycloalkane.
Other rules: If a ring is monosubstituted then no locant is required since the substituent
must be at C1. If a ring is polysubstituted then each substituent requires a locant to
unambiguously assign their relative positions.
2-cyclopropylbutane
ethylcyclohexane
1-ethyl-2-methylcyclohexane
Polycyclic alkanes
(1) Spiro ring systems: Spiro ring systems share a single common atom
spiro[2.2]pentane spiro[2.5]octane 5-methylspiro[3.5]nonane
(2) Fused ring systems: Fused ring systems share two or more common atoms,
bicyclo[1.1.0]butane
(3) Bridged ring systems: If there are more than two common atoms then the a "bridged" system is obtained.
bicyclo[2.2.1]heptane
Alkenes
Nomenclature Formula
Functional group suffix = -ene
Substituent name = alkenyl
propene
CH3CH=CH2
but-2-ene or 2-butene
CH3CH=CHCH3
cyclohexene 4-methylpent-2-ene or 4-methyl-2-pentene
(CH3)2CHCH=CHCH3
3-methylhex-3-ene or 3-methyl-3-hexene
Alkenes as substituents
In some cases, a group containing an alkene may need to be treated as a substituent.
In these cases the substituent is named in a similar fashion to simple alkyl substituents.
The method is required when the alkene is not the priority group.
The substituent is named in a similar way to the parent alkene.
It is named based on the number of carbon atoms in the branch plus the suffix -yl. i.e. alkenyl
There are two common names that are widely used:
Alkenyl group Common name Systematic name
CH2=CH- vinyl- ethenyl
CH2=CHCH2- allyl- 2-propenyl
CH3CH=CH- 1-propenyl
CH3CH=CHCH(CH=CH2)2 3-ethenylhexa-1,4-diene
CH2=CHH=CH2
buta-1,3-diene or 1,3-butadieneCH3CH=CHCH=CH2
(E)-penta-1,3-diene or (E)-1,3-pentadiene
CH3C(CH3)=CHH=CH2
2-methylpenta-1,4-dieneor
2-methyl-1,4-pentadiene
Alkynes
Nomenclature Formula
Functional group suffix = -yne
Substituent prefix = alkynyl
CH3CH2C≡CHbut-1-yne or 1-butyne
CH3C≡CCH3
but-2-yne or 2-butyne
CH3C≡CCH2C≡CHhexa-1,4-diyne
or1,4-hexadiyne
Alcohols
Nomenclature Formula
Functional class name = alkyl alcohol e.g. ethyl alcohol
Substituent suffix = -ol e.g. ethanol
Substituent prefix = hydroxy- e.g. hydroxyethane
CH3CH(OH)CH3
propan-2-ol or 2-propanol (or isopropanol)
CH2=CHCH2CH2OH
but-3-en-1-ol or 3-buten-1-ol
Primary amines Primary amines, NH2R may be named according to one of three methods as follows:
(a) by citing the name of the substituent group R as a prefix to the name of the parent hydride azane;
(b) by adding the suffix "-amine" to the name of the parent hydride RH;
(c) by adding "-amine" to the substituent name for the group R .
Examples to R-5.4.1
Ketones, thioketones, and their analogues R-5.6.2.1 Ketones. The generic term "ketone" refers to compounds containing a carbonyl group, >C=O, joined to two carbon atoms. Ketones are named substitutively by adding a suffix such as "-one", and "-dione" to the name of a parent hydride with elision of the final "e" of the parent hydride, if any, before "o". When a group having priority for citation as principal characteristic group is present, a ketone is described by the prefix "oxo-". Functional class names for monoketones and vicinal diketones, etc., are formed by citing the prefix names for the two groups attached to the carbonyl group(s) in alphabetical order followed by the class name "ketone", "diketone", etc., as a separate word.
Examples to R-5.6.2.1
Diketones derived from cyclic parent hydrides having the maximum number of noncumulative double bonds by conversion of two -CH= groups into >CO groups with rearrangement of double bonds to a quinonoid structure may be named alternatively by adding the suffix "-quinone" to the name of the aromatic parent hydride.
Example to R-5.6.2.1
Acyl derivatives of benzene or naphthalene have been named by changing the "-ic acid" or "-oic acid" ending of a trivial name of the acid corresponding to the acyl group to "-ophenone" or "-onaphthone". Only the names acetophenone, propiophenone, and benzophenone are retained in these recommendations (see R-9.1, Table 27(a)). Acyl derivatives of cyclic parent hydrides are named
by prefixing the substituent name derived from the cyclic parent hydride to the name of the acyclic ketone.
Example to R-5.6.2.1
Some trivial names are retained (see R-9.1, Table 27(a)).
R-5.6.2.2 Chalcogen analogues of ketones are named by using suffixes such as "-thione" and "-selone", and prefix names such as "thioxo-" and "selenoxo-". The use of prefixes such as "thio-" and "seleno-" with the trivial names of ketones, such as acetone, to indicate replacement of the ketonic oxygen atom with a chalcogen atom is not recommended.
Examples to R-5.6.2.2