32 Chapter 2 (e) CH3 Carbon:FC=4-号-2=-l HaC-p-CH3 CH3 Phosphorus:FC=5-0=+ (① Cs Nitrogen:FC=5-号-0=+1 0xy8geFC=6-号-6=-1 are different in the two forms. not resonance structures The pairs of structures in parts(b),(c),and(d)represent resonance forms. 2.34 (a) :0 Hc心G2 H6c一csch2 b (⊙)：NH2 NH2 NH2 H2N一2H2Nc2 The last resonance structure is a minor contributor because its carbon lacks a complete electron octet. (d) 0-§-Gn2→H6cs=cn2 ⊙H0=0H-0H=0H-6H-ct6·→Hk0=0H-dH-0H=0C1-CH H2C-CH=CH-CH=CH-CH3
Polar Covalent Bonds;Acids and Bases 33 2.35eeeonanceomsecateoioaiodecatoomse 2.36 CH3OH+HCI之CHOH2+C CHgOH Nat -NH2 CHgO:Nat+NH3 2.37 0: :0: = n of acetic acid is more acidic than the C-H hydrogens.The-OH than the-C-H bonds.In addition,the acetate anion is stabilized by resonance 2.38 The Lew Lewis acids:AIBr3.BH3,HF,TiCl4 Lewis bases:CH3CH2NH2,HgC-S-CH3 2.39 (a) (b)HH (c) :A:: H:B:H :Br: HHH H 、H (0 H (e)H H:C:S:C:H .C: H H :c:
34 Chapter 2 2.40 (a)CHgOH H2S0 CHgOH2*+HSO4 eake acid base (b)CHgOH NaNH2 CHgO Na*NH3 weaker base (c)CHaNHg*Cr+NaOH CHgNH2 H2O NaCl stronger stronger weaker weaker acid base base acid Only calcu CH3 Oxygen::Fc=6-子-6=- HC-N-9: CH3 Nitogen:FC5 --0=+1 (b) Nitrogen 1:FC 5--4=-1 Nitrogen 2:FC =5-0=+ Nitrogen 3:FC=5--2=0 C-N==: Nitrogen上：FC=5-9-2=0 Nitrogen 2:FC 5- 3 -0=+1 Nitogen3:c=5--4=-l 2.42 In maleic acid,the individual dipole moments add to produce a net dipole moment for the whole molecule.The individual dipole moments in fumaric acid cancel,resulting in a zero dipole moment. x00 HO- C-OH HO- H C=0 H OH Maleic acid Fumaric acid
Polar Covalent Bonds;Acids and Bases 35 2.43 The substances with the largest values of pa are the least acidic. Least acidic →Most acidic 0 00 pKa 19 pKa 9.9 pKa =9 pKa 4.8 2.44 To rea omp)with NaH,an acid must have a p at least 3 units of H2O.Thus,all substances in the previous problem except acetone react completely with NaOH. 2.46 CHa CH3 HgC-C-O-K*+H2O →H3C-C-OH+KOH CH3 pKa=15.7 stronger acid e prepare 2.47 2.48 (a)Acetone:Ka=5x 10-20 (b)Formic acid:Ka=1.8x 10-4 2.49 (a)Nitromethane:pKa=10.30 (b)Acrylic acid:pKa =4.25 2.50 Formic acid+H Formate í0.050M0 [x] x2 K2=1.8x10=0.050-×
36 Chapter 2 2.52 Sodium bicarbonate reacts with acetic acid to produce carbonic acid,which breaks down to 2.53aega但aR8e尚d2tan bases. →CH3OH2 acid 6 TiCl4 base as BH forms. 2.55 (a) (b) 0 H3C-N →H3C-N、 9=5-9:←→9-0=9 0:- :0: H2C=N=。→h2-N=N: