Name Your Molecule (IUPAC)

 

Rules for a Substitutive Nomenclature:

Systematic IUPAC Nomenclature

• Prefix (identity and position of substituents)

 

• Locants (numbers that define the position of substituents on the main, parent chain)

 

• Parent (Main chain of the molecule: based on its length as number of Carbon atoms)

 

• Suffix (based on the functional group having the highest priority,  it defines the class of compounds to which to molecule belongs)

 

 

Step 1 - Identify the parent hydrocarbon chain

 

The main chain is the longest hydrocarbon chain that bring the functional group having the highest priority:

If there are more than one chain, showing the same number of carbon atoms,

the main chain is the chain having the highest number of branching.

 

Step 2 - Number the parent chain carbon atoms

 

The parent chain carbon atoms are numbered

Start from the edge closest to the first branching point

If the chain is branched at the same distance, starting from both edges, the numbering starts form the edge closest to the second branching point

 

Step 3 - Identify and number substituents

Substituents are identified and numbered

Every substituent is given a number based on its branching position on the main chain

 

If on the same atom there are two substituents, each of them will have the same number

 

 

Step 4 - Write the name as a sinlge word:

 

Write the name as a unique word

dashes (-) are used to separate different prefixes and commas (,) to separate numbers

If there are two or more side chains or substituents, they are written following the alphabetic order

If there are two or more equal side chains or substituents, numbering prefix are used like: di-, tri-, tetra, etc.
These numbering prefix are not considered for the alphabetic order

 

 

Step 5 – Give a name to a complex substituent as it were itself compound:

When a substituent is complex (i.e branched)...
Start numbering the components of the complex substituents starting form its attaching point the the main chain.

When writing the name, the substituent name is placed between parentheses a ordered following the alphabetic order. (numbering prefixes are taken into accounts)

 

Alkyl Substituents

Alkyl Group or Alkyl Radical:
It is a partial structure which is derived form an alkane due to the extraction of an hydrogen atom.

Alkyl groups are named by substituting the suffix -ane with -yl.

Methane     →    Methyl
Ethane    →     Ethyl

 

Step 1 - Identify the parent hydrocarbon chain

 

The main chain is the longest hydrocarbon chain that contains the double bond. The suffix is  -ene:

 

 

Step 2 - Number the parent chain carbon atoms

 

Start form the edge closest to the double bond

           If the double bond is at the same distance form both edges, start form the edge closest to the first branching point

 

Step 4 - Write the name as a single word

Number the substituents in the main chain and write them in alphabetic order.

The double bond is indicated with the number of its first carbon (smallest number).

This number is positioned just before the parent hydrocarbon chain which will have the suffix –ene.

 

Cycloalkenes are numbered in a similar way

Start numbering by giving the smallest numnbber the alkene carbons (i.e 1 and 2)

The first substituent must have as low a number as possible

 

Step 1 - Identify the parent hydrocarbon chain

 

The main chain is the longest hydrocarbon chain that contains the triple bond
          The tyriple bond position is indicated by the first carbon of the alkyne, the suffix is -yne.

 

 

Step 2 - Number the parent chain carbon atoms

 

Number the parent chain carbon atoms

Start form the edge closest to the triple bond, and give it the smallest number as possible

Compounds having more than a triple bond are named -diynes, -triynes, etc.

Compounds containing both double and triple bonds are named  -enynes.

Start numbering enynes form the edge closets to a multiple bond (double or triple)

If both double and triple bonds could have the same number (i.e ambiguity in numbering), the double bond receive the lowest number

Alkyl, Alkenyl and Alkinyl Radicals

Substituents can contain multiple bonds:

 

Step 1 - Identify the parent hydrocarbon chain

 

Alkyl halides are numbers in the same way alkanes. The halogen atom is a substituent in the parent chain
 

 If there are multiple bond, the parent chain must contain them

 

Step 2 - Identify and number substituents

 

The main chain is numbered starting form the edge closest to the first substituent or branching point (i.e, alkyl or halide substituents have the same priority

 

a) If there are more halogen atoms of the same nature, everyone of them is numbered and the prefix di-, tri-, tetra- etc. are used

 

b) If there are more halogen atoms of different nature, all halogen atoms are numbered and they are indicated in alphabetic order

 

If one can start from both edges (step b), start form the edge closest start form the edge closest to the halogen (substituent) that comes first in alphabetic order

 

Generalities

Often aromatics did not follow systematic nomenclature

Monosubstituted benzenes are named as other hydrocarbons, using the suffix –benzene

If the alkyl substituent has a smallest or equal number of carbon atoms as the ring, the compound is named as an aromatic compound bearing an alkyl substituent

If the alkyl substituent has a greatest number of carbon atoms than the ring, the compound is named as an alkyl compound bearing an phenyl substituent

The name phenyl indicates –C₆H₅, when it is a substituent The group C₆H₅CH₂- is named benzyl

Disubstituted Benzenes: orto / meta / para nomenclature

 

Disubstituted benzenes are named with the prefixes:
      orto- (o), meta- (m), para- (p)

The nomenclature based on the prefixes orto-, meta-, para- is useful when, in considering reactions, one need to indicate where the reaction will occur (regioselectivity)

 

 

Polysusbstituted Benzenes

Benzene derivatives with more than two substituents are named by numbering the position of each substituent using the

numbers as low as possible. Substituents are indicated in alphabetic order.

 

Alcohol Classification: primary / secondary / tertiary

 

Alcohols can be classified as primary, secondary or tertiary

 

 

Step 1 - Identify the parent hydrocarbon chain:

 

The main chain is the longest hydrocarbon chain that  contains the hydroxyl group

the suffix is -ol

 

Step 2 - Number the parent chain carbon atoms

The parent chain carbon atoms are numbered starting from the edge closest to the hydroxyl group

Step 3 - Write the name as a single word:

 

Number the substituent based on their position on the parent chain and write the name positioning them in alphabetic order

 

Aldehydes

 

The aldehydes are named by substituting the final vocal of the parent alkane with the suffix -al

 

The parent chain must contain the –CHO group and this carbon atom takes the number 1

For more compelx aldehydes, where the –CHO group is linked directly to a ring, the suffix –carbaldehyde is used

 

 

 

Ketones

 

The ketones are named by substituting the final vocal of the parent alkane with the suffix -one

The parent chain must contain the ketone group and is numbered from the edge closest to the ketone

Some ketones have a trivial name

When the R-C=O groups is taken as a substituent, the name corresponding to the acyl group is used and the suffix -yl is added to the substituent

The name is taken from the parent carboxylic acid and the suffix is changed from -oic to -yl

 

If therea other functional groups and the ketone is taken as a substituent, it is named by using the prefix "oxo"

 

Carboxylic Acids

 

There are two types of Nomenclature based on the complexity of the acid

Straight chain acids are named by substituting the suffix -e of the parent alkane -oic followed by the word acid

The carboxyl carbon atom is always the first atom in the numbering sequence

When the carboxyl is linked to a ring, the suffix is -carboxylic followed by the word acid

There are several other trivial names that are commonly used

 

Nitriles

 

The compounds characterized by the presence of the -C≡ N functional group are named nitriles

They are related to the carboxylic acid by a similar reactivity

Their name is obtained by adding the suffix –nitrile to the name of the parent alkane and the carbon of the nitrile takes the number 1

 

The names of more complex nitriles are obtained by substituting the suffix -oic of the parent acid with the suffix -nitrile

 

When the –CN group is directly linked to a ring, the suffix -carboxylic of the parent acid is substituted with the suffix -carbonitrile

 

Acyl Halides

 

Acyl halides are named by writing the name of the acyl group followed by the name of the halide

The name of the acyl group comes from the name of the parent carboxylic acid and substituting the suffix -ic with the suffix -yl or -carboxylic with  -carbonyl

 

Anhydrides

 

Symmetric anhydrides, derived from monocarboxylic acids, and the cyclic ones, derived by dicarboxylic acids are named by substituting the word acid with the word anhydride

 

Symmetric anhydrides, derived from substituted monocarboxylic acids are named by adding the prefix bis- to the name of the acid

 

Unsymmetrical anhydrides derived from two different monocarboxylic acids are named by writing the names of the two acids in alphabetic order

 

Esters

 

The name of esters and salt of carboxylic acids is obtained in the same way

The suffix -ic is substituted by the suffix -ate and the name of the alkyl group (ester) or the cation (salt) is preceding the whole name

 

Amides

 

The amides that do not have any susbstituent on their nitrogen atom are named by substituting the suffix -ic or -oic of the parent acid with -amide or -carboxylic with -carboxamide

 

If the amide nitrogen atom bears alkyl / aryl substituents,  the alkyl / aryl substituent is placed before the name of the amide and its position as substituent is indicated by a capital N in italic.

 

 

Amines

 

Amines can be substituted with alkyl (alkylamines) or aryl (arylamines) groups

The chemistry of these two classes is similar but shows sometimes a few differences

Amines: Primary (RNH₂) Secondary (R₂NH) Tertiary (R₃N)

 

The terms primary, secondary and tertiary are used in a different way with respect to other compoudns (i.e. alcohols)
Here these terms indicate the degree of substitution of the Nitrogen atom

There are also compounds bearing four substituents on the nitrogen. The nitrogen bear also a positive charge. Those compounds are called quaternary ammonium salts

IUPAC Nomenclature of the Amines

 

In the IUPAC Nomenclature system the primary amines are named in different ways

Simple amines are named by adding the suffix -amine to the name of the alkyl substituent

Alternatively, the suffix -amine can be added in place of the final -e of the parent compound

When the molecule has more than a functional group the -NH₂ is considered an amine substituent of the base molecule

The name of secondary and tertiary symmetric amines is obtained by adding the prefix di- or tri- to the alkyl / aryl substituent

Secondary and tertiary unsymmetric amines are named as N-substituted primary amines

The longest alkyl group is taken as the main chain for reference name, while the other two alkyl groups are N-substituents

There only few trivial names for alkylamine but there are several for arylamines

as an example, very well known amines are aniline and toluidine

 

Heterocyclic Amines

Heterocyclic amines: compounds in which the nitrogen atom is part of a ring

In the numbering scheme, the nitrogen (at least one of them) bears the number 1