The structures shown are examples of Constitutional Isomer.
In Chemistry, an isomer refers to a molecule that is similar to another but has differences. These differences can be:
The molecules shown have the same formula because the elements in each pair are the same. However, the way these elements are connected is slightly different because the Br and the CH3 are connected to different carbons.
Based on this, the difference is the connectivity or constitution, and therefore these are constitutional isomers.
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