有机化学英文课件chapter4

1、uin 1884, svante arrhenius proposed these definitions a substance that produces h3o+ ions aqueous solution a substance that produces oh- ions in aqueous solution this definition of an acid is a slight modification of the original arrhenius definition, which was that an acid produces h+ in aqueous so

2、lution today we know that h+ reacts immediately with a water molecule to give a hydronium ionh h+ +( (a aq q) ) + + h h2 2o o ( (l l ) )h h3 3o o+ +( (a aq q) )h h y yd dr ro on ni iu um m i io on n a proton donor a proton acceptor+ +proton proton donor donor proton protonacceptoracceptor- -o oh hh

3、ho oh hh ho oh hh h+ + +o oh hh h+protonacceptorprotondonor+ohhohhnhhhhhh+nhh: the species formed from an acid when it donates a proton to a base the species formed from a base when it accepts a proton from an acid a proton-transfer reaction any pair of molecules or ions that can be interconverted b

4、y transfer of a protonh hc cl l ( (a aq q) )h h2 2o o ( (l l ) )c cl l- -( (a aq q) )h h3 3o o+ +( (a aq q) )+ + +w w a at te er rh h y yd dr ro og ge en nc ch hl lo or ri id de eh h y yd dr ro on ni iu um mi io on nc c h hl lo or ri id de ei i o on n( (b ba as se e) )( (a ac ci i d d) )( (c co on n

5、j ju ug ga at te ea ac ci id d o of f h h2 2o o ) )( (c co on nj ju ug ga at te eb ba as se e o of f h h c c l l) )c co on nj ju ug ga at te e a ac ci id d- -b ba as se e p pa ai ir rc co on nj ju ug ga at te e a ac ci id d- -b ba as se e p pa ai ir r brnsted-lowry definitions do not require water a

6、s a reactant consider the following reaction between acetic acid and ammonian n h h4 4+ +c ch h3 3c co o o oh hc ch h3 3c co o o o- -n n h h3 3+ + +a a c ce et ti ic c a ac ci id da a m m m m o on ni ia a( (a ac ci id d) )c co on nj ju ug ga at te e a ac ci id d- -b ba as se e p pa ai i r ra a c ce

7、et t a at te e i io on na a m m m m o on ni iu um mi io on n( (b ba as se e) )( (c co on nj ju ug ga at te e b ba as se ea ac ce et ti ic c a ac ci id d) )( (c co on nj ju ug ga at te e a ac ci id do of f a am m m m o on ni ia a) )c co on nj ju ug ga at te e a ac ci id d- -b ba as se e p pa ai i r r

8、 we can use curved arrows to show the flow of electrons in an acid-base reaction c ch h3 3- -c c- -o oo oh hn nh hh hh h c ch h3 3- -c c- -o o - -o oh h- -n n - -h hh hh h+ + +a a c ce et ti ic c a ac ci id d( (p pr ro ot to on n d do on no or r) )a a c ce et ta at te e i io on n: : : : : : : : : :

9、:a a m m m m o on ni ia a( ( p pr ro ot to on n a ac cc ce ep pt to or r) )a a m m m m o on ni iu um mi io on numany organic molecules have two or more sites that can act as proton acceptorsuin this chapter, we limit our discussion to carboxylic acids, esters, and amidesuin these molecules, the favo

10、red site of protonation is the one in which the charge is more delocalizeduquestion: which oxygen of a carboxylic acid is protonated?c ch h3 3- -c c- -o o - -h ho o+ + h h2 2s so o4 4c ch h3 3- -c c- -o o - -h hh ho o+ +c ch h3 3- -c c- -o o - -h hh ho o+ + + h h s so o4 4- -o or ra a( (p pr ro ot t

11、o on na at ti io on n o on n t th he e c ca ar rb bo on ny yl l o ox xy yg ge en n) )b b( (p pr ro ot to on na at ti io on n o on n t th he eh hy yd dr ro ox xy yl l o ox xy yg ge en n) )ufor protonation on the carbonyl oxygen, we can write three contributing structuresutwo place the positive charge

12、 on oxygen, one places it on carbonua-1 and a-3 make the greater contribution because all atoms have complete octetsuthe positive charge is delocalized over three atoms with the greater share on the two equivalent oxygens+ + + +c ch h3 3- -c c- -o o - -h ho oh hc ch h3 3- -c c- -o o - -h ho oh hc ch

13、 h3 3- -c co oh h+ + + +c ch h3 3- -c c- -o o - -h ho oc ch h3 3- -c c= =o o - -h ho oh hc ch h3 3- -c c= =o o - -h ho oh h+ +a a - -1 1( (c c a an nd d o o h ha av ve ec co om m p pl le et te e o oc ct te et ts s) )a a - -2 2( (c c h ha as s i in nc co om m p pl le et te e o oc ct te et t) )a a - -

14、3 3( (c c a an nd d o o h ha av ve ec co om m p pl le et te e o oc ct te et ts s) )ufor protonation on the hydroxyl oxygen, we can write two contributing structuresub-2 makes only a minor contribution because of charge separation and adjacent positive chargesutherefore, we conclude that protonation

15、of a carboxylic acid occurs preferentially on the carbonyl oxygenc ch h3 3- -c c- -o o- -h ho oh h+ +b b- -1 1c ch h3 3- -c c- -o o- -h ho oh h+ + +b b- -2 2( (c ch ha ar rg ge e s se ep pa ar ra at ti io on n a an nd da ad dj ja ac ce en nt t p po os si it ti iv ve e c ch ha ar rg ge es s) ) does p

16、roton transfer to an amide group occur preferentially on the amide oxygen or the amide nitrogen?c ch h3 3- -c c- -n n - -h hh ho o+ + h hc cl l+ +c ch h3 3- -c c- -n n- -h ho oh hh hh hc ch h3 3- -c c- -n n - -h hh ho o+ + + c cl l - -o or ra a( (p pr ro ot to on na at ti io on n o on n t th he ea a

17、m m i id de e o ox xy yg ge en n) )b b( (p pr ro ot to on na at ti io on n o on n t th he ea am m i id de e n ni it tr ro og ge en n) )a a c ce et ta am m i id de e( (a an n a am m i id de e) )uproton-transfer reactions occur with compounds having pi electrons, as for example the pi electrons of car

18、bon-carbon double and triple bondsuthe pi electrons of 2-butene, for example, react with hbr by proton transfer to form a new c-h bonduthe result is formation of a , a species in which one of its carbons has only six electrons in its valence shell and carries a charge of +1c ch h3 3- -c ch h= =c ch

19、h- -c ch h3 3 + + h h- -b br rc ch h3 3- -c c- -c c- -c ch h3 3 + + b br r - -h hh h+ +2 2- -b bu ut te en ne es se ec c- -b bu ut ty yl l c ca at ti io on n( (a a 2 2 c ca ar rb bo oc ca at ti io on n) )h h draw lewis structures for the two possible carbocations formed by proton transfer from hbr t

20、o 2-methyl-2-butenec ch h3 3- -c c= =c ch h - -c ch h3 3 + + h h- -b br r2 2- -m m e et th hy yl l- -2 2- -b bu ut te en ne ec ch h3 3uthe strength of an acid is expressed by an equilibrium constant uthe acid dissociation of acetic acid is given by the following equationh h3 3o o+ + +c ch h3 3c co o

21、- -o oh h2 2o o+ +c ch h3 3c co o h ho oa a c ce et ti ic c a ac ci id dw w a at te er ra a c ce et ta at te ei io on nh h y yd dr ro on ni iu um mi io on nuwe can write an equilibrium expression for the dissociation of any uncharged acid, ha, as:uwater is a solvent and its concentration is a consta

22、nt equal to approximately 55.5 mol/luwe can combine these constants to give a new constant, , called an h h a a + + h h2 2o o h h3 3o o+ + a a- - h ha a h h2 2o o k ke eq qa a- -+ + h h3 3o o+ += =k ke eq q h h2 2o o k ka a h h3 3o o+ + a a- - h h a a = = =h hi ii i- -h hb br rb br r- -h hc cl lc cl

23、 l- -h h2 2s so o4 4h hs so o4 4- -h h2 2o oh h3 3o o+ +h h3 3p po o4 4h h2 2p po o4 4- -c c6 6h h5 5c co oo o h hc c6 6h h5 5c co oo o- -c ch h3 3c co o o o h hc ch h3 3c co o o o- -h h2 2c co o3 3h hc co o3 3- -h h2 2s sh hs s- -n n h h3 3n n h h4 4+ +c c6 6h h5 5o o h hc c6 6h h5 5o o- -h hc co o

24、3 3- -c co o3 32 2- -c ch h3 3n n h h2 2c ch h3 3n n h h3 3+ +h h2 2o oh ho o- -c ch h3 3c ch h2 2o o h hc ch h3 3c ch h2 2o o- -h hc cc ch hh hc cc c- -h h2 2h h- -n n h h3 3n n h h2 2- -c ch h2 2= =c ch h2 2c ch h2 2= =c ch h- -c ch h3 3c ch h3 3c ch h3 3c ch h2 2- -a a c ci id df fo or rm m u ul

25、la ap pk ka ac co on nj ju ug ga at te e b ba as se ee et th ha an ne ea a m m m m o on ni ia ae et th ha an no ol lw w a at te er rb bi ic ca ar rb bo on na at te e i io on np ph he en no ol la a m m m m o on ni iu um m i io on nc ca ar rb bo on ni ic c a ac ci id da a c ce et ti ic c a ac ci id d3

26、 35 52 25 5b be en nz zo oi ic c a ac ci id dp ph ho os sp ph ho or ri ic c a ac ci id ds su ul lf fu ur ri ic c a ac ci id dh h y yd dr ro og ge en n c ch hl lo or ri id de eh h y yd dr ro og ge en n b br ro om m i id de eh h y yd dr ro og ge en n i io od di id de e5 51 13 38 81 10 0. . 3 33 31 15

27、5. . 7 71 15 5. . 9 94 4. . 7 76 66 6. . 3 36 69 9. . 2 24 49 9. . 9 95 5- -5 5. . 2 2- -7 7- -9 9- -8 84 4. . 1 19 92 2. . 1 1- -1 1. . 7 74 4h h y yd dr ro on ni iu um m i io on ns st tr ro on ng ge er rc co on nj ju ug ga at te e b ba as se ew w e ea ak ke er rc co on nj ju ug ga at te e b ba as

28、se ew w e ea ak ke er r a ac ci id ds st tr ro on ng ge er r a ac ci id dm m e et th hy yl la am m m m o on ni iu um m i io on n1 10 0. . 6 64 4h h y yd dr ro og ge en n s su ul lf fi id de e7 7. . 0 04 4a a c ce et ty yl le en ne eh h y yd dr ro og ge en ne et th hy yl le en ne e4 44 4uequilibrium

29、favors reaction of the stronger acid and stronger base to give the weaker acid and weaker basec ch h3 3c co o o o h hn nh h3 3c ch h3 3c co oo o- -n n h h4 4+ + + +a a m m m m o on ni ia a( (s st tr ro on ng ge er r b ba as se e) )a a c ce et ta at te e i io on n( (w w e ea ak ke er r b ba as se e)

30、)a a c ce et ti ic c a ac ci id dp pk ka a 4 4. . 7 76 6( (s st tr ro on ng ge er r a ac ci id d) )a a m m m m o on ni iu um m i io on np pk ka a 9 9. . 2 24 4( (w w e ea ak ke er r a ac ci id d) )p pk ke eq q = = 4 4. . 7 76 6 - - 9 9. . 2 24 4 = = - -4 4. . 4 48 8 k ke eq q = = 3 3. . 0 0 x x 1 10

31、 04 4uconsider the reaction between acetic acid and sodium bicarbonateuwe can write the equilibrium as a net ionic equationu we omit na+ because it does not undergo any chemical change in the reactionuequilibrium lies to the rightucarbonic acid forms, which then decomposes to carbon dioxide and wate

32、rc ch h3 3c co o h ho oh hc co o3 3- -c ch h3 3c co o- -o oh h2 2c co o3 3b bi ic ca ar rb bo on na at te e i io on na a c ce et ta at te e i io on na a c ce et ti ic c a ac ci id dp pk ka a 4 4. . 7 76 6( (s st tr ro on ng ge er r a ac ci id d) )c c a ar rb bo on ni ic c a ac ci id dp pk ka a 6 6.

33、. 3 36 6( (w w e ea ak ke er r a ac ci id d) )+ + +uthe overriding principle in determining the relative acidities of uncharged organic acids is the stability of the anion, a-, resulting from the loss of a protonuthe more stable the anion, the greater the acidity of hauways to stabilize anions inclu

34、de having the negative chargeuon a more electronegative atomuon a larger atomudelocalized through resonanceudelocalized by the inductive effectuin an orbital with more s charactera. electronegativity of the atom bearing the negative charge within a period, the greater the electronegativity of the at

35、om bearing the negative charge, the more strongly its electrons are held, the more stable the anion is, and the stronger the acidchhhnhho hethanepka 51methylaminepka 38methanolpka 16i conjugate basech3c hhch3n hch3o methylamide ionmethoxide ionethyl anionch3ch3ch3 acidb. size of the atom bearing the

36、 negative charge within a column of the periodic table, acidity is related to the size of the the atom bearing the negative charge atomic size increases from top to bottom of a column the larger the atom bearing the charge, the greater its stabilitys s h hc ch h3 3c ch h3 3o o c ch h3 3s s o oh hc c

37、h h3 3m m e et th ha an ne et th hi io ol lp pk ka a 7 7. . 0 0( (s st tr ro on ng ge er r a ac ci id d) )m m e et th ho ox xi id de e i i o on n( (s st tr ro on ng ge er r b ba as se e) )m m e et th ha an ne et th hi io ol la at te ei i o on n( (w w e ea ak ke er r b ba as se e) )m m e et th ha an

38、no ol lp pk ka a 1 16 6( (w w e ea ak ke er r a ac ci id d) )+c. resonance delocalization of charge in a- the more stable the anion, the farther the position of equilibrium is shifted to the right compare the acidity alcohols and carboxylic acids ionization of the o-h bond of an alcohol gives an ani

39、on for which there is no resonance stabilizationc ch h3 3c ch h2 2o o - -h hh h2 2o oc ch h3 3c ch h2 2o o - -h h3 3o o+ + +a a n n a al lc co oh ho ol la a n n a al lk ko ox xi id de e i io on n+ +p pk ka a = = 1 15 5. . 9 9 ionization of a carboxylic acid gives a resonance-stabilized anion the pka

40、 of acetic acid is 4.76 carboxylic acids are stronger acids than alcohols as a result of the resonance stabilization of the carboxylate anione eq qu ui iv va al le en nt t c co on nt tr ri ib bu ut ti in ng g s st tr ru uc ct tu ur re es s; ; t th he e c ca ar rb bo ox xy yl la at te e a an ni io on

41、 n i is s s st ta ab bi il li iz ze ed d b by yd de el lo oc ca al li iz za at ti io on n o of f t th he e n ne eg ga at ti iv ve e c ch ha ar rg ge e. .+ +c ch h3 3c co oo oc co oo oc ch h3 3o o h hc co oc ch h3 3h h3 3o o+ + +h h2 2o od. electron-withdrawing inductive effect the polarization of el

42、ectron density of a covalent bond due to the electronegativity of an adjacent covalent bond stabilization by the inductive effect falls off rapidly with increasing distance of the electronegative atom from the site of negative chargec c- -c ch h2 2o o - -h hh hh hh hc c- -c ch h2 2o o - -h hf ff ff

43、fe et th ha an no ol lp pk ka a 1 15 5. . 9 92 2, , 2 2, , 2 2- -t tr ri if fl lu uo or ro oe et th ha an no ol lp pk ka a 1 12 2. . 4 4c cf f3 3- -c ch h2 2- -o oh hc cf f3 3- -c ch h2 2- -c ch h2 2- -o o h hc cf f3 3- -c ch h2 2- -c ch h2 2- -c ch h2 2- -o oh h2 2, , 2 2, , 2 2- -t tr ri if fl lu

44、uo or ro o- -e et th ha an no ol l( (p pk ka a 1 12 2. . 4 4) )3 3, , 3 3, , 3 3- -t tr ri if fl lu uo or ro o- -1 1- -p pr ro op pa an no ol l( (p pk ka a 1 14 4. . 6 6) )4 4, , 4 4, , 4 4- -t tr ri if fl lu uo or ro o- -1 1- -b bu ut ta an no ol l( (p pk ka a 1 15 5. . 4 4) ) we also see the opera

45、tion of the inductive effect in the acidity of halogen substituted carboxylic acidsb bu ut ta an no oi ic c a ac ci id dp pk ka a 4 4. . 8 82 24 4- -c ch hl lo or ro ob bu ut ta an no oi ic ca ac ci id dp pk ka a 4 4. . 5 52 23 3- -c ch hl lo or ro ob bu ut ta an no oi ic ca ac ci id dp pk ka a 3 3. . 9 98 82 2- -c c h hl lo or ro ob bu ut ta an no oi ic ca ac