Question

Write the IUPAC name of the following:

Answer 1

Select the longest chain by counting the carbon atoms the chain may be shown in branched form or shown by putting molecular formula in compact form instead of writing in bond structure. Give numbering from that side where the functional group gets the lowest numbering. If there are more than one function group or alkyl group attached then put them in the lowest number sum.

Complete answer:
Here, in the above example which is given to us let’s count the largest number of carbon atoms. We will see that four carbons are put in a straight chain but two alkyl groups which are methyl and ethyl groups are also attached. So, our job is to count them also in such a way that we get the longest carbon chain at the end.

See, if we try to count the number of atoms we will get a total of five carbon atoms from ethyl group to the last carbon where in between we will have our functional group. Let’s start the numbering in such a way that the functional group gets the lowest number. We have two ways if we start the counting from methyl and the second way is to start it from ethyl. We will start our numbering from the methyl group such that the OH group gets the position- $2$ .

We will see that our numbering from purple color is from methyl to ethyl group. Now we name it as pent- for the five carbon atoms but there is substitution at carbon no $3$ by two methyl groups. So, we called it as $3,3$ -dimethylpent-$2$-ol.

Note: Try to give the numbering of atoms from that side where they will get the lowest number possible or sum will be lowest. Here, we use (-ol) because of the alcohol group. Instead of it we have given the aldehyde group there will be (-al) in place of (-ol). Aldehyde group carbon is counted as with the all carbon atoms and not alone.