210 ALKYNES 9.3 The bonds become shorter and stronger in the series as the electronegativity increases. NH HO N(3.0) O(3.5) F(4.0) Bond distance(pm) N-H(101) O—H(95) F-H(92) Bond dissociation energy (kJ/mol) H(435) )-H(497)FH(568) Bond dissociation energy (kcal/mol): N-H(104) O-H(119) F-H(136) 9. 4(b) A proton is transferred from acetylene to ethyl anion. CHCH CH, CH3 Ethyl anio (stronger acid) ker base)(weaker acid (pK26) (pKa=62) The position of equilibrium lies to the right. Ethyl anion is a very powerful base and depro- tonates acetylene quantitatively. (c) Amide ion is not a strong enough base to remove a proton from ethylene. The equilibrium lies ( weaker acid) ( weaker base) (d) Alcohols are stronger acids than ammonia; the position of equilibrium lies to the right CH,CCCH,O2H+NH, CHC≡CCI Amide ion (weaker base) on ammonia (weaker acid 9.5 (b) The desired alkyne has a methyl group and a butyl group attached to a-c=C-unit. Two alkylations of acetylene are therefore required: one with a methyl halide, the other with a butyl NaNH. N HC≡CH2CH2B NaNH2, NH, CH2C≡CH 2. CHCH, CH, CH, CHC≡CCH2CH2CHCH It does not matter whether the methyl group or the butyl group is introduced first; the order of steps shown in this synthetic scheme may be inverted (c) An ethyl group and a propyl group need to be introduced as substituents on a-C=C-unit. As in part(b), it does not matter which of the two is introduced first. HC≡CH 1. NaNH,, NH L NaN CHCh.CH Br CH3CH CHC=CH2CHCHB CH2CH,CHC≡CCH,CH Acetylene I-Pentyne 3-Heptyne Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website210 ALKYNES 9.3 The bonds become shorter and stronger in the series as the electronegativity increases. NH3 H2O HF Electronegativity: N (3.0) O (3.5) F (4.0) Bond distance (pm): N@H (101) O@H (95) F@H (92) Bond dissociation energy (kJ/mol): N@H (435) O@H (497) F@H (568) Bond dissociation energy (kcal/mol): N@H (104) O@H (119) F@H (136) 9.4 (b) A proton is transferred from acetylene to ethyl anion. The position of equilibrium lies to the right. Ethyl anion is a very powerful base and depro￾tonates acetylene quantitatively. (c) Amide ion is not a strong enough base to remove a proton from ethylene. The equilibrium lies to the left. (d) Alcohols are stronger acids than ammonia; the position of equilibrium lies to the right. 9.5 (b) The desired alkyne has a methyl group and a butyl group attached to a @C>C@ unit. Two alkylations of acetylene are therefore required: one with a methyl halide, the other with a butyl halide. It does not matter whether the methyl group or the butyl group is introduced first; the order of steps shown in this synthetic scheme may be inverted. (c) An ethyl group and a propyl group need to be introduced as substituents on a @C>C@ unit. As in part (b), it does not matter which of the two is introduced first. 1. NaNH2, NH3 2. CH3CH2CH2Br Acetylene 1-Pentyne 3-Heptyne HC CH 1. NaNH2, NH3 2. CH3CH2Br CH3CH2CH2C CH CH3CH2CH2C CCH2CH3 1. NaNH2, NH3 2. CH3Br Acetylene Propyne 2-Heptyne HC CH 1. NaNH2, NH3 2. CH3CH2CH2CH2Br CH3C CH CH3C CCH2CH2CH2CH3 Amide ion (stronger base) NH2 Ammonia (weaker acid) Ka1036 (pKa 36) NH3 2-Butyn-1-olate anion (weaker base) CH3C CCH2O 2-Butyn-1-ol (stronger acid) Ka 10161020 (pKa 1620) CH3C CCH2O H Ammonia (stronger acid) Ka 1036 (pKa 36) NH3 Vinyl anion (stronger base) CH2 CH Amide ion (weaker base) NH2 Ethylene (weaker acid) Ka 1045 (pKa 45) CH2 CH H CH3CH3 Ethane (weaker acid) Acetylide ion (weaker base) HC C Ethyl anion (stronger base) CH2CH3 Acetylene (stronger acid) HC C H Ka 1026 (pKa 26) Ka 1062 (pKa 62) Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website