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Mircea Darabantu CHIMIE ORGANICA an II Ing. CURS-VIII Pag.<br />
4e π 2e π<br />
Δ<br />
acetilena<br />
(filodiena)<br />
[4 + 2]<br />
Stare de 1,4-Ciclohexadiena<br />
tranzitie ciclica<br />
EXEMPLU DE CICLOADITIE [4 + 2] DIELS-ALDER TOTAL D I A S T E R E O S P E C I F I C A<br />
4e π<br />
4e π<br />
H CO-OEt<br />
+<br />
H CO-OEt<br />
2eπ Dietil maleat<br />
(cis, filodiena)<br />
Δ<br />
H CO-OEt<br />
+<br />
EtO-OC H<br />
2eπ Dietil fumarat<br />
(trans, filodiena)<br />
H<br />
H<br />
Stare de<br />
tranzitie<br />
Δ<br />
CO-OEt<br />
CO-OEt<br />
H<br />
EtO-OC<br />
Stare de<br />
tranzitie<br />
CO-OEt<br />
H<br />
H<br />
H<br />
CO-OEt<br />
CO-OEt<br />
Produs<br />
CIS pur<br />
H<br />
CO-OEt<br />
H<br />
CO-OEt<br />
Produs<br />
TRANS pur<br />
5<br />
4<br />
1<br />
2<br />
Dietil maleat<br />
(cis, filodiena)<br />
Dietil fumarat<br />
(trans, filodiena)<br />
Produs<br />
CIS pur<br />
Produs<br />
TRANS pur<br />
Proces TOTAL DIASTEREOSPECIFIC<br />
- cicloaditii [2 + 2] la care participa doua alchene sau doi compusi nesaturati cu o dubla legatura, fiecare cu<br />
cate 2 electroni π : au loc numai in conditii fotochimice de exemplu:<br />
.<br />
2e π<br />
. .<br />
2e π<br />
hν<br />
[2 + 2]<br />
. .<br />
..<br />
Stare de ciclobutan<br />
tranzitie ciclica<br />
6