The following compound is an intermediate in the synthesis of a gelator, which is a compound capable of self-assembling to form a gel in an organic liquid (Soft Matter 2012, 8, 5486–5492).
(b) In Chapter 4, we will learn that molecules generally rotate freely around single bonds, while rotation around double bonds is significantly restricted. Consider the four single bonds connecting the two rings in this structure. Two of them can rotate freely, while the other two cannot. Identify the two with restricted rotation and justify your answer by drawing resonance structures.