Question

Explain why a change in the position of a substituent group (i.e., which carbon the group is attached to) can, but does not always, result in a different compound

Answer 1

A change in the position of a substituent group can result in a different compound only if it alters the connectivity of the atoms. Otherwise, it will still be the same compound.

Step-by-step explanation:

A change in the position of a substituent group can, but does not always, result in a different compound. This is because the identity and structure of a compound are determined by the connectivity of its atoms.

If the change in position of the substituent group alters the connectivity of the atoms in the compound, then it will result in a different compound. However, if the change in position does not alter the connectivity, then it will still be the same compound.

For example, in a benzene ring, there are three possible disubstituted benzenes, and they can be distinguished using numbers to indicate the relative positions of the substituents. These different positions result in different compounds.

Answer 2

Changing the position of the substituents in an organic molecule will often result in a different chemical compound. If the structure of the molecule changes but it still has the same molecular formula, i.e., the same number of each atom, then this is called a structural isomer. However, it is possible to change the position of a substituent and the structure of the molecule remain unchanged. This would most likely occur in symmetric molecules.

CH₃ - CH₂ - CH₂ - CH₂ - OH 1-butanol

CH₃ - CH₂ - CH - CH₃ 2 - butanol
|
OH

Looking at the two structures above, the position of the -OH was moved from the 1-carbon to the 2-carbon, resulting in two different molecules. These are structural isomers. However, we can also move the -OH group without changing the molecule.

CH₃ - CH₂ - CH - CH₃ 2-butanol
|
OH
CH₃ - CH - CH₂ - CH₃ 2-butanol
|
OH
In the above structure, it appears that the -OH group was moved from the 2-carbon to the 3-carbon, but since this molecule is symmetrical, the 2- and 3-carbons are equivalent. Therefore, swapping substituents has no effect on the structure of the molecule and these are equivalent.