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4.41 From Table 4.2, the pKₐ for NH₄⁺ is 9.24 and the for a carboxylic acid is about 5. Therefore a carboxylic acid is a stronger acid than ammonium ion and the equilibrium favors the product. The product is an internal salt and should have salt-like properties, such as a high melting point and a high solubility in water. 4.42 The N that is bonded to the C=O group is not very basic because its electron pair is stabilized by resonance with the C=O group. For this reason, the N of an amide is not very basic. The other N has no special stabilization for its unshared electron pair and is approximately as basic as the N of ammonia. 4.43 The electrons on the N with the H are part of the conjugated pi system and are not very basic. The electrons on the N without the H are in an AO that is perpendicular to the pi system. These electrons are not involved in resonance and are much more basic. 4.44 The NH₃⁺ is an inductive electron-withdrawing group and increases the acid strength of the nearby carboxylic acid group. 4.45 The anion has two resonance structures. The conjugate acid of this anion can have the proton on the or on the C. O: base HO: base 4.46 a) Isomer b is more stable than a because it is conjugated and has resonance stabilization. b) The conjugate base of a has three resonance structures. Protonation at one of the carbons bearing a partial negative charge produces a and protonation at the other produces b. 61