Question

Writing the Structural Formula from the IUPAC Name.

Answer 1

This can be achieved according to the following steps. 

(i) Locate the root word and write down the parent carbon chain. Draw straight parent carbon chain. Number the carbon chain from either end. However, in case of chain-terminating functional groups, carbon bearing functional group must be included in the parent carbon chain and must be numbered 1. 

(ii) Locate the primary suffix (-ane, -ene, or -yne) and insert the double or triple bond (if any) at the carbon atom indicated by the suffix. 

(iii) Locate the suffix of the primary functional group and insert the proper functional group on the specified carbon atom indicated by the prefix in the given name. In case it does not carry any numeral prefix, it is assumed to be located at C₁. 

(iv) Locate the secondary functional group(s), substituent(s) and side chain(s) indicated by suffixes and insert them on the specified carbon atom(s) indicated by prefixes. 

(v) Lastly, add suitable number of hydrogen atoms to satisfy four valencies of each carbon atom in the chain.

Let us apply these rules on an example.

Write down the structural formula for 7-hydroxy-3-ethoxy-4, 5-dimethyl-hept-5-enal or 7-hydroxy-3-ethoxy-4, 5-dimethyl-5-heptenal.

(i) Here the root is hept and thus parent carbon chain must have 7 carbon atoms, ie., the compound is a derivative of heptane. Note that the secondary suffix -al denotes the chain-terminating -CHO group, carbon atom of the -CHO group must be included in the carbon chain and must be given number 1 on numbering the carbon chain. 

Thus the carbon chain of the compound can be written as below.

(i) Here the root is hept and thus parent carbon chain must have 7 carbon atoms, ie., the compound is a derivative of heptane. Note that the secondary suffix -al denotes the chain-terminating -CHO group, carbon atom of the -CHO group must be included in the carbon chain and must be given number 1 on numbering the carbon chain. Thus the carbon chain of the compound can be written as below.

\(\overset {7}{C} - \overset {6}{C} - \overset {5}{C} - \overset {4}{C} - \overset {3}{C} - \overset {2}{C} - \overset {1}{C} HO\)

(ii) The primary suffix - ene indicates the presence of a double bond at C₅. Hence, the above chain can be written as

\(\overset {7}{C} - \overset {6}{C} = \overset {5}{C} - \overset {4}{C} - \overset {3}{C} - \overset {2}{C} - \overset {1}{C}HO\)

(iii) The name indicates the presence of one-OH group at C₇, one-OC₂H₅ group at C₃ and two methyl groups at C₄ and C₅. Attaching these substituents on the specified carbon atoms, we get 1

(iv) Finally, by adding suitable number of hydrogen atoms to satisfy four valencies of each carbon atom, we get