Indeed, dione B satisfies the spectroscopic criteria. Carbonyl bands are seen in the infrared spec-trum, and compound B has two sets of protons to be seen in its 1H NMR spectrum. The two vinylprotons are equivalent and appear at low field, 6.7 ppm; the 4 methylene protons are equivalent toeach other and are seen at 2.9 ppm.Compound B is the doubly ketonic tautomeric form of hydroquinone, compound C, to which itisomerizes on standing in water.24.29A reasonable first step is protonation of the hydroxyl oxygen.The weak oxygen–oxygen bond can now be cleaved, with loss of water as the leaving group.This intermediate bears a positively charged oxygen with only six electrons in its valence shell. Like
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