At 36°8C the NMR resonances for the ring methyl groups of “isopropylmesitylene” (protons H^a and H^b in the following structure) are two singlets at δ 2.25 and δ 2.13 with a 2 : 1 intensity ratio, respectively. When the spectrum is taken at 260°8C, however, it shows three singlets of equal intensity for these groups at δ 2.25, δ 2.17, and δ 2.11. Explain these results.

Transcribed Image Text:

H H₂C CH3 CH3 a CH3 CH3 "isopropylmesitylene"