chuong 4. co che pu

8/8/2019 Chuong 4. Co Che Pu

1/21

Chng 4:Cc phn ng hu c -Phn loi phn ng -

C ch phn ng

Qu trnh thay i (t chc li) orbital PT di

nh hng ca nhng K bn ngoi & bn trong vi s

to thnh h thng mi khc bit vi trng thi ban

u ca cc n/t trong PT v c tnh nng lng &v tr tng h

Cc yu t nh hng ti vP: to, p sut, xc tc

a. Bn cht & cu trc ca cc cht trung gian

Phn ct ng ly

A B A B+

- Xy ra th kh, trong dung mi khng

phn cc

- Xc tc: to, nh sng, peroxyd

- Gc t do: CH3, C2H5, Cl ....

- 1 -


2/21

Phn ct d ly

+ BAA B -

+ BAA B -+

- C mang in tch (+) carbocation. VD:

CH3+

CH3 CH CH3+

- C mang in tch (-) carboanion. VD:

CH2CHO-

(H CH2CHO + OH- CH2CHO

-+ H2O

- P d ly (P ion) xy ra trong dung mi

phn cc

- Xc tc: acid hoc base

b. Cu trc & bn ca cc cht trung gian

Gc t do R. thng c cu trc phng, 1 s c

cu trc hnh thp

.

C

- 2 -


3/21

CH3 < CH3CH2< (CH3)2CH< (CH3)3C

CH3< C6H5CH2< (C6H5)2CH< (C6H5)3C

Carbocation R+

- Cu trc phng:

C+

- bn: in tch (+) gii to bn tng+I, +M lm tng bn

VD: +I CH3+ < CH3CH2+< (CH3)2CH+ RBr > RCl > RF

- Dn cht Hal ho bc 1 hoc 2 (R cng nh cng t

b cn tr khng gian)

- SP thu c c cu hnh ngc vi cht ban u

(nghch o Walden)

_+ Br

R1

CHO

H

R2nhanh

R2 R1

BrHO C

H

chm_HO

H

R2

R1

C Br

- 9 -


10/21

c. Th i nhn ni phn t SNi:

VD P th OH bng Cl khi alcol tc dng vi

thionyl clorid:

C OH

R2

R

R1+ SOCl2 C Cl

R2

R

R1+ +SO2 HCl

v = k [R

OH] [SOCl2] R

= RR1R2C

C ch P:

SOCl2+C OH

R2

R

R1 (1)

(- HCl) C

O

R2

R

R1 S O

Cl

(2)

C Cl

R2

R

R1+ S O

O

(I) (II)

3.1.2. P th i e SE (Electrophilic Substitution)

a. P th i e n PT S1: 2 giai on:

R Xchm

R- X++

R- E+ R E+ nhanh

v = k [RX]

- 10 -


11/21

VD thng xy ra C bo ho:

CH3 C CH3

O

+Br2OH-

O

C CH2BrCH3 + HB

CH3 C CH3

O

chm/OH-C CH2

O

CH3

O

C CH2CH3..

..nhanh/ Br2+

O

C CH2BrCH3

-HBr

b. P th i e lng PT SE2:

Thng xy ra hydrocarbon thm

S chung:

H++

E

E+

H

C ch P:

+ E+ E+

phc

H

E

phc

+

E

sn phm t

- H+nhanh chm nhanh

- 11 -


12/21

P hal ho, nitro ho, sulfon ho, alkyl ho, acyl

ho vo nhn benzen: SE

VD: P bromo ho benzen

++Fe

HBrBr2Br

C ch P:

[FeBr4]-

+Br+FeBr3+Br Br

Br+

phc

H

Br

phc

Br+Br++- H+

1.3. Phn ng th gc SR (Radical Substitution)

hp cht nohydro th bi hal, NO2

Xc tc: nh sng

S P:

RH + Br2 h R Br + HBr

C ch P:

- Giai on khi mo:

h+ BrBrBrBr

- Pht trin dy chuyn:- 12 -


13/21

Br+R BrBr Br+R

RBr HBr++HR

- Tt dy chuyn:

R BrBrR

Br BrBrBr

+

+

R R+ RR

Phn ng SR l phn ng dy chuyn

Phn ng SR thng to ra hn hp cc sn phm

khc nhau.

2. Phn ng cng hp

Phn ng cng hp l qu trnh chuyn lin kt

thnh lin kt .

2.1. Cng hp i in t AE (Electrophilic

Addition)

Phn ng cng hp ca halogen vo alken:

C C

Br

Br

(CCl4)Br Br+C C

Phn ng qua giai on to phc v phc (l

mt carbocation):

- 13 -


14/21

C C C C C C

Br

C C

Br

Br

Br Br+

chm

Br Brd (+) d (-)

phc

phc

nhanh+ Br

sn ph

+ P cng hp trans

+ cng hp brom vo cyclohexen:

Br

Br

Br2+

trans-1,2-dibromocyclohexan

P cng hp ca tc nhn bt i HX vo alken bt

i:

R CH CH3X

HX+R CH CH2

Quy tc Markovnikov: H ca HX lun cng hp

vo n/t C mang nhiu H nht.

P theo hng to thnh carbocation trung gian bn

nht:

- 14 -


15/21

R CH2 CH2+

R CH CH3+ X-

R CH CH3X(carbocation bc 2 bn hn)

(carbocation bc 1 km bn)H+R CH CH2

2.2. Cng hp i nhn AN (Nucleophilic

Addition)

nhm carbonyl >C=O ca aldehyd, ceton:

C OH

A

HA+C O

(HA = HOH , HOR , HCN , HSO3Na , ...)

C OH

A

H+C O

Anhanh

A+ (-) (+) chm

C O

cyanohydri

C OH

CN

C O

CN

H+C N+C O

2.3. Cng hp gc AR (Radical Addition)

VD:

R CH2 CH2Brperoxyd

to

HBr+R CH CH2

C ch P:

- 15 -


16/21

2ROto

RO OR

B+ROH+RO H Br

(II)

(I)

R CH CH2Br

R CH CH2Br

(2)

(1)

Br+R CH CH2

bn hn

Br+R CH2 CH2 BrHBr+R CH CH2Br

P cng hp clor vo benzen:

Cl

ClCl

ClCl

Cl

h+ 3Cl2

hexaclorocyclohexanC ch P:

2Clh

Cl Cl

Cl

ClCl

ClCl

ClCl+

Cl

ClCl2Cl

Cl

nhng tiu phn mang in tch dng tn

cng vo nhng vng c mt in t ln, c gi

l tc nhn i in t (electrophile). phn ng i

- 16 -


17/21

in t l tt c cc phn ng c khi ng bi

tn cng ban u ca mt tc nhn i in t.

Cc tiu phn mang in tch m tn cng

vo nhng vng ngho in t ca phn t, c gil tc nhn i nhn (nucleophile). Phn ng i nhn

l cc phn ng c khi ng bi tn cng ban

u ca tc nhn i nhn.

Cc phn ng ion c s can thip ca mt yu t

i nhn v mt yu t i in t v mt i khi

kh bit chc chn tiu phn tn cng.

4.4.3. Phn ng tch loi E (Elimination)

Phn ng tch loi l phn ng trong c hai

nguyn t hoc nhm nguyn t b loi khi phn t

m khng c thay th bng nhng nguyn t hoc

nhm nguyn t khc.

Thng th hai nhm b loi t hai nguyn tcarbon cnh nhau v sn phm ca phn ng l cc

hp cht khng no:

C C

H X- HX

C C

X = Cl , Br , I , OCOCH3 , OH2 , SR2, NR3

- 17 -


18/21

Mt trong hai nhm b loi thng l hydro ( dng

proton). Cc phn ng tch loi ch yu l: loi

hydrohalogenid t dn cht halogen, loi nc t alcol,

phn tch mui amoni bc bn...Tu thuc vo cu to ca R trong RX v iu

kin phn ng, cc phn ng tch loi c th xy ra

theo c ch n phn t (E1) hoc lng phn t

(E2).

Phn ng tch loi v phn ng th i nhn lun

tranh chp nhau.

4.4.3.1. Tch loi n phn t (E1)Nu gc R trong RX l bc ba (hoc bc hai), dung mi phn cc mnh,

phn ng xy ra qua giai on to hp cht trung gian l carbocation (nh phnng SN1).

V d phn ng tch loi HBr t tert-butyl bromid di tc dng ca base mnhto ra isobuten:

Phn ng tng qut:

CCH3

CH3

CH3Br

OH

- HBrCCH3

CH2

CH3

C ch: Phn ng qua 2 giai on:a. Giai on chm: dn cht halogen b ion ho chm to ra

carbocation:

CCH3CH3

CH3Br

chmCCH3CH3

CH3+ Br

b. Giai on nhanh: base mnh ( ca KOH) tch mt proton ca

carbocation to thnh H2O v mt alken:

- 18 -

OH


19/21

OH

CCH3CH2

CH3

H

+

nhanhCCH3CH2

CH3H2O +

Giai on chm to carbocation l giai on quyt nh tc phn ng,nn tc ch ph thuc vo nng ca dn cht halogen:

v = k1 [(CH3)3CBr]

V d khc: Phn ng tch loi nc t alcol bc ba di tc dng ca acid mnh,to ra alken:

Phn ng tng qut:

CCH3CH3

CH3OH

acid mnh+H2O CCH3

CH2

CH3

alcol tert-butylic isobuten

C ch phn ng nh sau:Phn ng bt u bng gn proton vo nhm OH:

CCH3CH3

CH3OH

H+CCH3CH3

CH3O H

H

Phn ng tip din qua hai giai on:a. Giai on chm: alcol c proton ho b ion ho chm to ra nc v

carbocation:

+ H2OCCH3CH3

CH3chmCCH3CH3

CH3O H

H

b. Giai on nhanh: carbocation mt mt proton to ra alken:

CCH3CH2

CH3

H

- H+CCH3CH2

CH3

4.4.3.2. Tch loi lng phn t E2Nu gc R trong dn cht halogen RX l bc mt (hoc bc hai), c mt

ca base mnh, phn ng xy ra qua trng thi chuyn tip.V d phn ng tch loi HBr t dn cht alkyl bromid bc mt di tc dng

ca base mnh, to ra alken:

R CH2 CH2 Br + OHKOH/alcol

R CH CH2 + H2O + Br

C ch phn ng:tn cng vo proton carbon , trong khi in tch m ca n

c phn b trn phn t b tn cng, to ra trng thi chuyn tip. S chuyn

- 19 -

OH


20/21

dch in tch m v pha halogen dn n phn ct cc lin kt: HC v

CBr to ra alken, km theo nc v ion :

C CH

H H

H

Br

R

HO

chmC

H

H

R

HO (-)(-)

C

H

H

Br

nhanh

trng thi chuyn ti

HOH + +C CH

R

H

HBr

Tc ca phn ng t l vi nng ca RX v ion OH: phn ng bchai.

v = k2 [RX] [OH]

V d khc: tch loi phn t H2O t alcol bc mt bi acid mnh, to raalken:

R CH2 CH2 OH( H2SO4)

R CH CH2 + H2O

Trc tin, nhm OH alcol c proton ho to ra cation. Sau base lin hpHSO4 tn cng vo hydro carbon , to ra acid sulfuric, alken v nc:

R CH2 CH2 O HH+

R CH2 CH2 O H

H

R CH CH2 O H

HH

HSO4

H2SO4 + + H2OR CH CH2

Ch : - Phn ng tch loi E2 xy ra ch yu vi cc cu trc bc mt.Cc dn xut bc hai theo c ch thay i, bao gm E1, E2.

- V mt ho lp th, cc thnh phn c tch loi phi nm trncng mt mt phng v c cu hnh ngc nhau. Do qu trnh ny c tn ltch loi trans (tn gi ny khng xt on cu trc ca alken c to ra).

H

HRBr

H HC C

H

H

R

H

Br

H

- HBrC C

H H

HR

- Phn ng tch loi thng xy ra theo quy tc Zaixep: Phn ng tchloi ca dn cht halogen v alcol xy ra theo hng to thnh alken c nhiunhm th nht (alken bn nht). Ni mt cch khc: "hydro c tch ra t carbon mang t hydro nht".

V d:

- 20 -

Br


21/21

R CH2 CH CH3X

- HXR CH CH CH3

R CH2 CH CH2

85%+

15%

4. Phn ng chuyn v (Rearrangement)

Phn ng chuyn v l phn ng gy ra s thay i v tr ca mt sthnh phn cu trc (nguyn t, nhm chc, lin kt bi) trong phn t.

Phn ng chuyn v thng xy ra theo c ch d ly. Phn ng chuyn vtheo c ch gc t gp trong ho hu c.

Cc phn ng chuyn v c chia thnh hai nhm:- Chuyn v khng gy ra s thay i b khung carbon.- Chuyn v gy ra s thay i b khung carbon.

chuong 4. co che pu

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