Question

Select the complete IUPAC name for the following compound, including the correct (R) or (S) designation

• (R)-3-chloro-3-methyl-4-ethylhexane 

• (R)-3-chloro-4-ethyl-3-methylhexane 

• (S)-3-chloro-4-ethyl-3-methylhexane 

• (S)-3-chloro-3-methyl-4-ethylhexane

Answer 1

Concepts and reason

The concepts used to solve the solution are IUPAC naming of organic compounds and R/S nomenclature. Systematic method of naming an organic compound is known as IUPAC nomenclature system. IUPAC naming involves several steps for naming such as identification of parent chain, numbering of carbon atoms, naming substituents and side chains etc. Absolute configuration is used to give the information of the substituents and chirality of an organic molecule.

Fundamentals

Parent chain is the longest carbon chain in the compound. The groups attached to the parent chain are known as substituents.

R/S nomenclature is used to determine the stereo chemical configuration of a compound. Compounds are designated as R or S based on their orientation towards right or left.

The parent chain contains 6 carbon atoms and hence the base name is hexane.

There are 3 different substituents attached to the parent chain. One methyl group, one ethyl group and one chlorine atom. Methyl group and chlorine atom is on the same carbon i.e. the 3rd carbon. Ethyl group is attached to the 4th carbon. Chlorine atom comes first by name, followed by ethyl and methyl group.

Therefore, the name of the compound is 3-chloro-4-ethyl-3-methylhexane.

Consider the atoms directly attached to the stereo center. The third Carbon is the stereo center. It is attached to a Cl atom, a methyl group, an ethyl group and chain of 5 carbon atoms (which is denoted as R in Picture).

Prioritize the four atoms and number them 1 to 4 based on their priority. Substituent with higher atomic number take first priority. Here Cl takes the first priority. Since the other two substituents (C atoms attached to the stereo center) are of equal rank, determine the chain with connection to an atom with highest priority. Here, the chain R has 5 carbon atoms. Therefore, it has the second highest priority followed by ethyl group. The lowest priority substituent i.e. methane is pointed away using dashes.

Now draw an arrow from number 1 to number 4.

Since the orientation of arrow is clockwise, it is an R-enantiomer.

Ans:

The name of the compound is (R)-3-chloro-4-ethyl-3-methylhexane.