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4.24 The stability of the conjugate base depends on factors such as the electronegativity and the hybridization of the atom where the electrons are located, resonance delocalization of the basic electrons, and inductive effects of nearby groups. a) O is more electronegative than C. CH₃CH₂O: b) A carboxylic acid is a stronger acid than an : alcohol because of resonance stabilization of its conjugate base. : c) O is more electronegative than C or N. H₂NCH₂CH₂-O: 4.25 According to the Lewis acid-base definition, an acid is an electron pair acceptor. Any compound that has an unfilled valence orbital is a potential Lewis acid. a) The boron atom in has an empty orbital that can accept electrons. Therefore it is a Lewis acid. b) Methane is not a Lewis acid since there are no empty orbitals in the valence shell of any of its atoms. c) The positively charged carbon atom of this species is sp² hybridized, and has an empty p orbital that can accept electrons. Therefore it is a Lewis acid. 4.26 According to the Lewis definition, a base is an electron pair donor. Any compound that has an unshared electron pair can behave as a Lewis base. a) can b) cannot c) can d) cannot e) can 4.27 pKₐ = -log Kₐ a) 3.76 b) 50 4.28 Kₐ = (antilog of a) 1 X 10⁻²⁵ b) 4.9 X 10⁻¹⁰ 4.29 a) In both cases the conjugate bases are stabilized by an inductive effect and by resonance. However, the compound on the right is the stronger acid because the hydrogen is removed from the more electronegative oxygen atom. b) The hydrogen on sulfur is more acidic than the one on oxygen, so the compound on the left is a stronger acid. 55