Question

How to name organic compounds using IUPAC NOMENCLATURE

Answer 1

1. Recognise the functional group in the compound. This will determine the suffix of the name (see Table).

   Functional group	suffix
   alkane	-ane
   alkene	-ene
   alkyne	-yne
   alcohol	-ol
   aldehyde	-al
   ketone	-one
   carboxylic acid	-oic acid
   ester	-oate

   Table 4.5: The suffix associated with various functional groups.

2. Find the longest continuous carbon chain that contains the functional group (it won't always be a straight chain) and count the number of carbon atoms in this chain. This number will determine the prefix (the beginning) of the compound's name.

   Carbon atoms	prefix
   1	meth-
   2	eth-
   3	prop-
   4	but-
   5	pent-
   6	hex-
   7	hept-
   8	oct-
   9	non-
   10	dec-

   Table 4.6: The prefix of a compound's name is determined by the number of carbon atoms in the longest chain that contains the functional group.

3. Number the carbons in the longest carbon chain (Important: If the molecule is not an alkane (i.e. has a functional group) you need to start numbering so that the functional group is on the carbon with the lowest possible number). Start with the carbon at the end closest to the functional group.

4. Look for any branched groups:

   • Name them by counting the number of carbon atoms in the branched group and referring to Table 4.6, these groups will all end in -yl.
   • Note the position of the group on the main carbon chain. If there is more than one of the same type of branched group then both numbers must be listed (e.g. 2,4 -) and one of the prefixes listed in Table 4.7 must be used. Important: If the molecule is an alkane the branched group must be on the carbon with the lowest possible number.
   • The branched groups must be listed before the name of the main chain in alphabetical order (ignoring di/tri/tetra).

   If there are no branched groups this step can be ignored.

   Number	prefix
   2	di-
   3	tri-
   4	tetra-

   Table 4.7: Prefixes for multiple substituents with the same name. These apply to multiple functional groups as well.

5. For the alkyl halides the halogen atom is treated in much the same way as branched groups:

   • To name them take the name of the halogen atom (e.g. iodine) and replace the -ine with -o (e.g. iodo).

     Halogen	name
     fluorine	fluoro
     chlorine	chloro
     bromine	bromo
     iodine	iodo

     Table 4.8: Naming halogen atoms in organic molecules.

   • Give the halogen atom a number to show its position on the carbon chain. If there is more than one halogen atom the numbers should be listed and a prefix should be used (e.g. 3,4-diiodo- or 1,2,2-trichloro-). See table for a list of the prefixes.
   • The halogen atoms must be listed before the name of the main chain in alphabetical order (ignore di/tri/tetra).

   If there are no halogen atoms this step can be ignored.

6. Combine the elements of the name into a single word in the following order:

   • branched groups/halogen atoms in alphabetical order (ignoring prefixes)
   • prefix of main chain
   • name ending according to the functional group and its position on the longest carbon chain.

Naming hydrocarbons (ESCKJ) Naming alkanes

The suffix for an alkane is -ane.