Question

A.Draw the structures of all isomeric alcohols of molecular formula ${C_5}{H_{12}}O$ and give their IUPAC names.
B.Classify the isomers of alcohols in above question as primary, secondary and tertiary alcohols.

Answer 1

Hint :The isomers are compounds having the same molecular formula but different structures. The structure can be different if there is some positional difference in the structure, the connectivity can be different. Try to make as different structure possible by the molecular formula ${C_5}{H_{12}}O$ you can name the compound so that one compound would not repeat again.

Complete step-by-step answer:A.Pentanol is alcohol having five carbon atoms and one OH group. There are eight structural isomers possible when connectivity of any atom changes. Let’s start with the straight chain Pentanol, having five carbons in a straight line and one OH at position one. We can make the position of alcoholic group change from $1\,\,to\,2$ .
We get one isomer when all five carbon are connected by covalent bond in a straight line having an alcoholic group at position $1$ called as Pentan-$1 - ol$ . Next we can connect the alcoholic group at position two and three from there we get two more isomers called Pentan-$2 - ol$ and Pentan-$3 - ol$ .
Now if carbon atoms and alcoholic groups both change their position we get many isomers like shown in figure. When one carbon atom get connected to carbon no. $3$ we get $2 - $methylbutan- $1 - ol$ similarly we get a total of eight isomer with molecular formula ${C_5}{H_{12}}O$ .

B.If we want to classify the isomer as primary secondary and tertiary we have to see the carbon atom by which alcoholic group is connected. After seeing that carbon see from how many carbon atoms it is connected further. If it is connected with only one carbon atom it is called as primary alcohol, if it is connected with two carbon atoms it is called as secondary alcohol and last if it is connected to three carbon atoms then it is called as tertiary alcohol.

Note: The connectivity of carbon having alcoholic groups will give an estimate above the primary, secondary and tertiary alcohols. In the above figure the carbon atom is connected with two more carbon thus it is referred to as secondary alcohols. We can easily distinguish these in alkyl halides, in those cases carbon which is having halogen with it connects with one, two and three carbon atoms and gives primary, secondary and tertiary alkyl halides respectively.