Question

Write the IUPAC name of the following compound:
${{H}_{3}}C-CH(Cl)-C{{H}_{2}}-CH=C{{H}_{2}}$

Answer 1

Try to recall that the IUPAC name of any organic compound essentially consists of word root, suffix and prefix. The word root has the parent alkane chain.

Complete step by step answer:
- We know that IUPAC system is the most rational and widely used system in organic chemistry. The most important feature of this system is that any given molecular structure has only one IUPAC name.
- The IUPAC name of any organic compound essentially consists of three parts:
- Word root: It is the basic unit of name. It denotes the number of carbon atoms present in the parent chain (the longest possible continuous chain of carbon atoms including the functional group and multiple bonds) of organic molecules.
So, here, the longest carbon chain contains 5 atoms of carbon, so we can say that the word root for this compound is ‘pent-’

- Suffix: A primary suffix is added to word root to indicate whether the carbon chain is saturated or unsaturated and a secondary suffix is then added to the primary suffix to indicate the nature of the functional group present in the organic compound.
Here, one double bond is present in the carbon chain, so the name of this molecule will have the suffix ‘-ene’.
- Prefix: A primary prefix is used to simply distinguish cyclic from a cyclic compound and a secondary prefix is added immediately before the word root in alphabetical order to denote the side chains or substituent groups.
In this molecule, one chloride is attached to the parent carbon chain, so the name will contain the prefix ‘chloro-’ along with its position on the carbon chain
- If any multiple bonds are present in the parent chain, then number the carbon atoms of the parent chain as 1,2,3,4......etc. starting from the end which gives the lowest number to the carbon atom involved in multiple bonds. So we will mark the compound as:
${{H}_{3}}{{C}_{5}}-{{C}_{4}}H(Cl)-{{C}_{3}}{{H}_{2}}-{{C}_{2}}H={{C}_{1}}{{H}_{2}}$
And not as:
${{H}_{3}}{{C}_{1}}-{{C}_{2}}H(Cl)-{{C}_{3}}{{H}_{2}}-{{C}_{4}}H={{C}_{5}}{{H}_{2}}$

We can see that the double bond is present on the first carbon so we will mark its location between the word root and the suffix.
The chlorine atom is present in the fourth carbon atom, so we will mark its location even before the prefix. So, the final IUPAC name of this compound will be:
4-chloropent-1-ene.

Note: Note that when an organic compound contains two or more different functional groups, one of the functional groups is selected as primary functional group while all other groups are treated as substituents. Also, you should remember that the names of acyclic compounds are obtained by adding the prefix, ‘cyclo’ to the name of corresponding straight chain hydrocarbons.
Here, we can also omit adding the 1 marking the position of the double bond since if there is no number present, then it is implied that the bond is present on the first carbon atom. Do not omit writing down the location of the double or triple bond if its location is on any carbon other than the first carbon.