The IUPAC name of the compound CH3CH(CH3)CHCH2 is?

A. 2 – methyl but – 1 – ene
B. 2 – methyl but – 2 – ene
C. 3 – methyl but – 1 – ene
D. 3 – methyl but – 2 – ene

Correct Answer:

Option C = 3 – methyl but – 1 – ene

Explanation

– Recognise the functional group in the compound. This will determine the suffix of the name

– 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

– 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.

– 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.

– 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)
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 4.7 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.

– 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.