Question

An alkene $\left( {{{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}} \right)$ on ozonolysis gave acetaldehyde and acetone as the product. Write the IUPAC naming of the alkene.

Answer 1

We know that IUPAC name is the standard naming of organic compounds following a set of guidelines. IUPAC name of a compound consists of three parts, prefix, word root and suffix. Word root indicates the number of carbon atoms in the longest chain, suffix denotes the functional group and prefix denotes the substituents present in the compound.

Complete step by step answer:
Let’s first understand the ozonolysis reaction in detail. Ozonolysis is the reaction in which breaking of unsaturated bonds of alkyne, azo compound or alkenes takes place in presence of ozone.

Now, we discuss the ozonolysis of alkenes. The oxidation of alkene with ozone gives aldehyde or alcohol or ketone or carboxylic acid.

One example of ozonolysis reaction of alkene is,

Here, R is an alkyl group.

Here, we have to find the structure of alkene whose chemical formula is ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$ and on ozonolysis, it gave acetaldehyde and acetone as the product.

In the above diagram, if we replace ${{\rm{R}}_{\rm{1}}}$ by ${\rm{C}}{{\rm{H}}_{\rm{3}}}$ group, ${{\rm{R}}_{\rm{2}}}$ by ${\rm{C}}{{\rm{H}}_{\rm{3}}}$ group and the H (C2) by ${\rm{C}}{{\rm{H}}_{\rm{3}}}$ of the reactant (alkene), the new alkene form is,

The ozonolysis reaction of the above alkene is,

So, we can say that the alkene gives acetaldehyde and acetone on ozonolysis.

Now, we have to write the IUPAC name of the alkene.

There are four carbon atoms in the longest chain. So, the word root in the IUPAC name is ‘but’. The functional group alkene is present in C2. So, the suffix will be ‘2-ene’. There is one methyl substituent present at C2. So, the prefix will be 2-methyl. IUPAC name is in the form of prefix+word root+suffix

So, the IUPAC name of the compound is 2-methyl-but-2-ene.

Note:
Always remember that, when more than one functional group is present in a compound then only one functional group is considered as principal functional group and remaining functional groups are considered as substituents. The principal functional group is chosen on the basis of order of preference. The arrangement of some functional group in order of decreasing priority is,

-COOH, $- {\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{H}}$ ,-COOR, -COCl, $- {\rm{CON}}{{\rm{H}}_{\rm{2}}}$ , -CN, $- {\rm{HC}} = {\rm{O}}$, ${{\rm{R}}_1}{{\rm{R}}_2}{\rm{ - C}} = {\rm{O}}$ ,-OH, $- {\rm{N}}{{\rm{H}}_{\rm{2}}}$ , ${\rm{C}} = {\rm{C}}$ , ${\rm{C}} \equiv {\rm{C}}$