1559r.ah06_099-11210/22/0520:19Page108 108 chapter 6 PROPERTES AND REACTIONS OF HALOALKANES:BIMOLECULAR NUCLEOPHILIC SUBSTTTUTON (e)(1)-NH2>PH2 NH, (2)PH2 >-NH2 NH Size puts "PH,first:lack of charge puts NH,last ()NH>-PH,>-NH, Reverse of () (d)(1)-OCN >-SCN (basic) (2)SCN>OCN Size (larger atom is more nucleophilie) (3)-SCN>-OCN Revese of (I). (e)(1)HO->CH;S->F- n CH,S"E (2)CH3S->HO->F- Large size of CHS takes precedence for nucleophilicity. (F->CH S->HO They'eall bad.f( (f)(1)NH H2O>H2S (②H,S>NH>H0 Size.then clectronegativity (3)H2S H2O>NHa Reverse of () 43.(a)No reaction.Starting material is an alkane.Alkanes don't react with nucleophiles. (b)CH CH.OCH H of the prod (c)CH3 pe.Draw t esses H入 CH: C-CH (e)No reaction.The leaving group would beOH,a strong base.Strong bases are very poor leaving groups. (f)No(or ely slow)reaction.Now the leavin (h)(CHs)CHCH CH2SCN.Leaving group is (i)No reaction.NHis a bad leaving group. (j)CH;NH2 ms).and,therefore,cannot serve as a source or nding.108 • Chapter 6 PROPERTIES AND REACTIONS OF HALOALKANES: BIMOLECULAR NUCLEOPHILIC SUBSTITUTION (c) (1) NH2  PH2  NH3 (2) PH2  NH2  NH3 (3) NH3  PH2  NH2 (d) (1) OCN  SCN (2) SCN  OCN (3) SCN  OCN (e) (1) HO  CH3S  F (2) CH3S  HO  F (3) F  CH3S  HO (f ) (1) NH3  H2O  H2S (2) H2S  NH3  H2O (3) H2S  H2O  NH3 43. (a) No reaction. Starting material is an alkane. Alkanes don’t react with nucleophiles. (b) CH3CH2OCH3 (c) (d) (e) No reaction. The leaving group would be OH, a strong base. Strong bases are very poor leaving groups. (f ) No (or extremely slow) reaction. Now the leaving group is good (CH3SO3 ), but HCN is a weak acid and therefore a very poor source of CN nucleophiles. (g) Finally, everything is right for a reaction to occur. Both a good leaving group (CH3SO3 ) and a good nucleophile (CN) are present, so the product (CH3)2CHCN forms readily. (h) (CH3)2CHCH2CH2SCN. Leaving group is (i) No reaction. NH2 is a bad leaving group. (j) CH3NH2 44. (a) BMIM is polar (very! It is an ionic salt!) and aprotic (it lacks hydrogens attached to electronegative atoms), and, therefore, cannot serve as a source of
hydrogens for hydrogen bonding. CH3 S O O O CH3CH2 CH3S CH3 C H CH3 CH3 I    A good conformation of the product after inversion of the reacting carbon. Immediately following SN2 displacement, the molecule possesses an eclipsed shape. Draw it! Reverse of (1). Size, then electronegativity. Electronegativity, then size. They’re all bad. Order is reverse of (1). Large size of CH3S takes precedence for nucleophilicity. HO stronger than CH3S because of size, and stronger than F because of electronegativity difference. Comparison between CH3S and F hard to make as small size favors F, whereas lower electronegativity favors CH3S. Reverse of (1). Size (larger atom is more nucleophilic). Size (smaller atom is more basic). Reverse of (1). Size puts PH2 first; lack of charge puts NH3 last. Larger size makes PH2 a weaker base than NH2; lack of charge makes NH3 the weakest. 1559T_ch06_099-112 10/22/05 20:19 Page 108