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9. Механизмы реакций алифатического нуклеофильного замещения PowerPoint PPT Presentation


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9. Механизмы реакций алифатического нуклеофильного замещения. S N 1 и S N 2. 9.1. Ионные пары и влияние растворителя 9.2. Карбокатионы и их перегруппировки 9.3. Нуклеофильность 9.4. Уходящие группы (нуклеофуги) 9.5. Стереохимия влияние пространственных факторов и соседних групп

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9. Механизмы реакций алифатического нуклеофильного замещения

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9

9.

SN1 SN2

9.1.

9.2.

9.3.

9.4. ()

9.5.

9.6.


9

9.1.

-

()

,


9

Goering, H.L.; Levy, J.F. J.Am.Chem.Soc., 1964, 86, 120

80%-

100 k/krac = 2.3. N3- k, krac.


9

SN


9

9.2.

pKR+

R+ + H2O

ROH + H+

pKR+ = log ([R+]/[ROH]) + HR ( ) ( )

HR . HR ~ .


9

pKR+ SN1


9

pKR+

,


9

, ~ 10-15 /


9

1,2- ( )


9

1,2-


9


9

9.3.


9

N+ = lg k lgk0

(Ritchi, P.O.I., Virtanen, J.Am.Chem.Soc., 1972, 94,4966)

N+ - ; lg k CH3Br CH3I, (Ph3C+, ArN2+, .) ; lgk0 - ( HO- H2O). N+ -. - (1953)


9


9

(Mayr, H.; Platz, M. Angew.Chem.Int.Ed., 1994, 33,938)

lg k = s(N + E).

k - 2- 20 Ar2CH+ () ( = 0 4,4-- ); s -

E ~ 1.241 lg kw 5.8; kw . Ar2CH+ H2O 20.

(Phan, T.B.; Breugst,M.; Mayr, H. Angew.Chem. Int.Ed., 2006, 45,3869)

lg k = sEsN(N + E); sE ; sN . sE = 1 ( ) - ; sE = 0.6 ( n-). sE = 1 sN = 0.6 lg k = 0.6N + 0.6E, - .

(http://www.cup.uni-muenchen.de/oc/mayr/reaktionsdatenbank/)


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()

  • , (OH- > H2O, NH2- > NH3)

  • , , (NH2- > RO- > OH- > R2NH > ArO- > NH3 > > F- > H2O > ClO4-; R3C- > R2N- > RO- > F-)

  • I- > Br- > Cl- > F- , . : Cl- > Br- > I-. : HO- > F- ~ MeO- > MeS- >> Cl- > CN- > Br-.

  • .

4. a- : , -: HOO- > HO-, NH2NH2 > RNH2


9


9

-, , .. , .

CH3Br + HO- ( )

CH3Br + HO- (H2O) CH3OH + Br-ksolv = 2.3x10-25cm3/mol

CH3OH + Br- k = 1.0x10-9 cm3/mol

-, SN2

.

Me3CO- , MeO- EtO-, -


9

9.4. ()

, . , .

HO- RO- , H2O ROH ( ) . SN1cA SN2cA (cA conjigate acid, 1 2).

(): N2, O3ClO-, TsO-, FSO3-, CH3SO2O-(MsO), CF3SO2O- (TfO)


9

NH2, NHR ?

R-NH2 + TsCl

RNTs2

R-NH2 + HONO

R-N2+

Katrizky, A. 1983


9

9.5. ,

SN2 :


9

SN1 SN2

15%

65%

: (. 9.1) ()

33%

38%

38%


9

(1) (2) (3)

k 1 10-6 10-14

SN2 . (2) (3) , ( )


9

, b- SN2 . b- RCOCH2X NCCH2X,


9

R2NCH2CH2Cl ( )


9

SNi


9

9.6.


9

,

1. R-X + Nu: R-Nu + X: , : C > N > O > S. SN .

2. : .


9

SN1 R3C+, SN2 R3C-X. R3C+ R3C-X . SN1 , , SN2 - . , SN1 SN2 CN-, N NO2-, C=C-O- Ph-O-.


9

3. Ag+ Na+, K+ , , , SN1 . :

R-Hal + AgCN R-NC

R-Hal + NaCN RCN

4. , (O > N > C) ( -). , .


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