SolutionsPhysical and Bond Properties
1. Anhydride or acid
Acetic anhydride (mass 102) boils at 140 °C and acetic acid (mass 60) at 118 °C. Is this consistent with the acid forming dimers?
Yes: the acid dimer has mass 120 and behaves like a molecule of that size; the anhydride, of similar mass and without hydrogen bonds, boils at a similar temperature.
2. Resonance
Why is the resonance of the central oxygen with each carbonyl weaker in an anhydride than in an ester?
The lone pair of the central oxygen is shared between two carbonyls that compete for it, so each receives less electron density: that is why anhydrides are more reactive than esters.