1559T_eh25.439-45310/20/055:59 AM Page442 442 chapter 25 HETEROCYCLES:HETEROATOMS IN CYCLC ORGANIC COMPOUNDS Br 一 30.The order of basicity is the reverse of the order of the acidity of the conjugate acids (pk values shown below the structures). Bases <0<〔<N<Ho H Weakest base Strongest base Conjugate acids >NH*>H2O nk. 00 rone “”心 Alvdouble bondsone lone pairbclecnsall areomtie All have stronger bases than pyrrole.Then, the acylium ion converts the ether oxygen into a good leaving group and allows SN2 displacement by bromide to occur. 30. The order of basicity is the reverse of the order of the acidity of the conjugate acids (pKa values shown below the structures). Bases Conjugate acids 31. All have two double bonds plus one lone pair in a p orbital  6
electrons, so all are aromatic. All have sp2 -hybridized lone pairs on nitrogen, not tied up in the aromatic
system, and therefore available to act in a Lewis-base manner. Pyrrole lacks an sp2 -hybridized lone pair; therefore all the compounds above are stronger bases than pyrrole. 32. (a) (b) O CH3 N N N H p sp2 N N H p sp2 S p N sp2 N sp2 O p H3O NH4  H2O Weakest acid H   H  Strongest acid pKa  4.4 0.0 5.3 9.2 15.7 N H  N H H2O Weakest base Strongest base HO   NH3 N H N CH3 CH3 Br   O  O C H3C H H CH3 O O C Configuration is inverted here (SN2) Br H3C H3C H H 442 • Chapter 25 HETEROCYCLES: HETEROATOMS IN CYCLIC ORGANIC COMPOUNDS 1559T_ch25_439-453 10/20/05 5:59 AM Page 442