Iupac Nomenclature

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

Longest chain

•

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.

•

The longest continuous chain containing the principle functional group defines the root name. Other groups attached to this chain are called substituents.

•

Numbering (i.e. assigning locants)

•

If there are two chains of equal length, then the choice that gives the simplest substituents is chosen.

•

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 suffix This is added to the end of the name based on the principle functional group. Root This defines the number of atoms (usually carbon atoms) in the longest continuous chain that contains the principle functional group. Substituent prefix Any groups other than the principle functional group are substituents and are added to the beginning of the name in alphabetical order. Multiplier If a group occurs more than once, a simple multiplier (e.g. di, tri, tetra, etc.) is used to indicate how many times it occurs.

Locants Locants 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 = methC2 = ethC3 = propC4 = butC5 = pentC6 = hexC7 = heptC8 = octC9 = nonC10 = decC11 = undecC12 = dodecC16 = hexadecC18 = octadecC20 = 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 1 R-X 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

R-F

Functional Group -X halo

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 Functional group suffix = -ane

Formula

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. CH3CH3CH2CH3CH2CH2CH3CH2CH2CH2CH3CH2CH2CH2CH2-

methyl ethyl propyl butyl 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 = CH3CH2CH2CH2CH2CH2the symbol "R" is commonly used to generically represent an alkyl group, e.g. R-X Structural formula

Name

CH3-

methyl-

CH3CH2-

ethyl-

CH3CH2CH2-

propylor n-propyl

(CH3)2CH-

isopropyl-

CH3CH2CH2CH2-

butylor

Generic line drawing

n-butyl CH3CHCH2CH3

sec-butylor 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, RCH3-

Common name methyl-

Complex name (if different)

CH3CH2-

ethyl-

CH3CH2CH2-

propyl-

(CH3)2CH-

isopropyl-

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)-

(1-methylethyl)-

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 Functional group suffix = -ene

Formula

Substituent name = alkenyl

propene CH3CH=CH2

but-2-ene or 2-butene CH3CH=CHCH3

cyclohexene

4-methylpent-2-ene or 4-methyl-2pentene (CH3)2CHCH=CHCH3

3-methylhex-3ene 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-

CH3CH=CHCH(CH=CH2)2

CH2=CHH=CH2

buta-1,3-diene or 1,3-butadiene

1-propenyl

3-ethenylhexa-1,4-diene

CH3CH=CHCH=CH2

(E)-penta-1,3-diene or (E)-1,3pentadiene

CH3C(CH3)=CHH=CH2

2-methylpenta-1,4-diene or 2-methyl-1,4-pentadiene

Alkynes Nomenclature Functional group suffix = -yne

Formula

Substituent prefix = alkynyl

CH3CH2C≡CH but-1-yne or 1-butyne

CH3C≡CCH3 but-2-yne or 2-butyne

CH3C≡CCH2C≡CH

hexa-1,4-diyne or 1,4-hexadiyne

Alcohols Nomenclature Functional class name = alkyl alcohol e.g. ethyl alcohol

Formula

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 R­5.4.1 

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 R­5.6.2.1 

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 R­5.6.2.1 

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 R­5.6.2.1 

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 R­5.6.2.2