Notions of nomenclature for the use of the exercises on this site

 

The classification of organic compounds in the manner recommended by IUPAC requires you to make some remarks when there relates to a method for proposing a database-based exercises.


Alkyl residue "trivial names" such as tert-butyl or Isopropyl can create ambiguity, when you must assign a name to a molecule. In other words, can be used? Since it is not strictly "IUPAC expressions, when you want to build an educational system based on a database, you must make choices. The site database, can use these "trivial names". It will therefore be borne in mind that according to IUPAC, such groups may be appointed as 1-methylethyl (isopropyl) and 1,1-dimethylethyl (tert-butyl). You need so caution in assigning names. Please consider that, when you will find two or more substitutents whose name can be “trivial” you have two choices to build the whole molecular name. You can decide to use trivial or IUPAC names for those subsituents, but not both, in the same name. You can define a name having all substituents named by the trivial way or by IUPAC nomenclature system but not a mixture of the two methods.

As a second point, please remember that because often you write complex and long names, you have to pay attention to what you type on the keyboard. Often the correct typing can make all the difference.


Finally, as advice to Italian students who want to face with the nomenclature in the English language, which it is hoped since this is the nomenclature that is used in the chemical literature, you should put a lot of attention to the writing of the names, due to differences between the two languages (one for all: esano - hexane). For this purpose you can use as a reference this link.

Systematic Nomenclature

 

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)

 

 

Alkanes

Step 1 - Identify the parent hydrocarbon chain

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.

 

Alkenes

Step 1 - Identify the parent hydrocarbon chain

Step 1 - Identify the parent hydrocarbon chain

 

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

 

Alkynes

Step 1 - Identify the parent hydrocarbon chain

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.

 

 

Alkyl Halides

Step 1 - Identify the parent hydrocarbon chain

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

 

Aromatic Compounds

Generalities

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

Alcohols

Alcohol Classification: primary / secondary / tertiary

Alcohol Classification: primary / secondary / tertiary

 

Alcohols can be classified as primary, secondary or tertiary

 

 

Ethers and Epoxydes

Simple common Ethers

Simple common Ethers

 

Simple Etehrs, not having any other functional groups are named on the base of the organic susbtitutents and by adding the word ether


 

 

Aldehydes and Ketones

Aldehydes

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

 

 

Carboxylic Acids and their Derivatives

Carboxylic Acids

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

 

 

Amines

Amines

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