1559T_ch09_148-17410/30/0518:03Pa9e155 ⊕ EQA Solutions to Problems.155 which C-bond breaks,but the direction of also react with basic nuc .This is an S2 process that displaces an alkoxide. nng str the energy content sucn t tively charge tdeucpisctioe to small-ring ctbers brea ote Small E. *0 c+CH,一CH :-CHz-CHz-O Nue-CH3 +O-CHs Reaction coordinate- 9-10.Sulfur Analogs of Alcohols and Ethers This short section expands on the obvious parallels between oxygen and sulfur that arise as a result of their relationship in the periodic table.As you saw earlier.the larger sized atoms are more nucleophilic.bu ess ba cludes a variety of oxidized species.Common examples are SO2 and HSO.New systems introduced here in- clude sulfonic acids(RSO3H).sulfoxides(RSOR).and sulfones(RSO2R). Solutions to Problems 25.Equilibrium always lies on the side with the weaker acid-base pai (a)Left;(b)left;(c)right:(d)right. 26.(a)CH,CH,CH,I (b)(CH)CHCH,CH,Br (Both by S2 mechanisms) (d)(CH CH)CCl (Both by Sxl mechanisms) Solutions to Problems • 155 apply in a clear-cut way: SN1 considerations determine which COO bond breaks, but the direction of approach of the nucleophile (back-side attack) is characteristic of an SN2 process. Strained cyclic ethers also react with basic nucleophiles. This is an SN2 process that displaces an alkoxide, which is a very bad leaving group. The nucleophile has to be a good one because the leaving group (a negatively charged alkoxide ion) is a terrible one. The reaction follows the SN2 reactivity order of 1°  2°  3°. Normally alkoxides cannot be displaced in SN2 reactions. In oxacyclopropanes, however, ring strain raises the energy content such that suitably reactive nucleophiles can displace negatively charged oxygen leaving groups (see graph, below). The only reason this reaction occurs at all is that the displacement reaction breaks open a small, strained ring. Please note that this is a reaction unique to small-ring ethers. Unstrained ethers are unreactive toward basic nucleophiles. 9-10. Sulfur Analogs of Alcohols and Ethers This short section expands on the obvious parallels between oxygen and sulfur that arise as a result of their relationship in the periodic table. As you saw earlier, the larger sized atoms are more nucleophilic, but less ba￾sic. Thus comparisons of the chemical properties of pairs of species like HS
vs. HO
, H2S vs. H2O, and CH3SH vs. CH3OH are straightforward. Larger atoms are also more readily oxidized, and sulfur chemistry in￾cludes a variety of oxidized species. Common examples are SO2 and H2SO4. New systems introduced here in￾clude sulfonic acids (RSO3H), sulfoxides (RSOR), and sulfones (RSO2R). Solutions to Problems 25. Equilibrium always lies on the side with the weaker acid-base pair. (a) Left; (b) left; (c) right; (d) right. 26. (a) CH3CH2CH2I (b) (CH3)2CHCH2CH2Br (Both by SN2 mechanisms) (c) (d) I (CH3CH2)3CCl (Both by SN1 mechanisms) 1559T_ch09_148-174 10/30/05 18:03 Page 155