2/9/2010. anti aromatic. non aromatic. Aromatic = stabilization due to cyclic deolcalization of electrons.

Transcription

1 rrange the followng wth respect to ncreasng stablty due to π- electron delocalzaton? romatc = stablzaton due to cyclc deolcalzaton of ant non ant lots of delocalzaton no delocalzaton some delocalzaton molecular orbtal theory: a revew. n mportant falure of smple resonance theory s the nablty to predct the nstablty of cyclobutadene. molecular orbtal theory: a revew. only overlap between p orbtals on postons and. lots of delocalzaton no delocalzaton OMO OMO n mportant success of smple molecular orbtal theory s the ablty to predct the nstablty of cyclobutadene. Does the nteracton of two flled molecular orbtals (OMO-OMO nteracton) result n stablty for butadene?. yes. no Usng ths model, what s the orgn of stablty of butadene? OMO OMO OMO OMO re OMO- nteractons allowed? OMO- nteractons are allowed and predct stablzaton of benzene by electron delocalzaton.

2 llow overlap between postons and as well as and. The molecular orbtals of benzene OMO OMO OMO- nteractons are forbdden because of the symmetry of the molecular orbtals!!! OMO OMO Can I do these molecular calculatons? ückel

3 ückel s Rule: Cyclc compounds wth n + π-electrons wll be stablzed by cyclc delocalzaton. ückel s Rule: Cyclc compounds wth n + π-electrons wll be stablzed by cyclc delocalzaton. Chose those compounds predcted by ückel s Rule to be stablzed by the cyclc delocalzaton of Snce benzene has 6 π-electrons ückel s rule (n = ) predcts benzene to be stablzed by the cyclc deolcalzaton of Does cyclobutadene obey ückel s rule? C. + D. E. F. ückel s Rule: Cyclc compounds wth n + π-electrons wll be stablzed by cyclc delocalzaton. Chose those compounds predcted by ückel s Rule: to be stablzed by the cyclc delocalzaton of Whch order has the followng compounds correctly arranged wth respect to ncreasng acdty < < < < C < < D < < E < < F < < Whch order has the followng compounds correctly arranged wth respect to ncreasng acdty. Whch of the followng molecules would ückel s rule predct pk a + 6 6π n anon! + ~0 + ~50 < < < < C < < D < < E < < F < < () + + () + (C) + (D) (E) (F)

4 Whch of the followng molecules would ückel s rule predct Whch of the followng molecules would ückel s rule predct () + + () + (C) + (D) (E) (F) () + + () + (C) + (D) (E) (F) Whch of the followng compounds would you predct to be more basc? Whch of the followng ntrogen atoms n mdazole would you predct to be more basc? + + pk a = 5. pk a =. pk a (5.7 kj/mol) = pk a = (. 5.)(5.7 kj/mol) = 8.5 kj/mol). Draw the two catons that are formed by protonatng each ntrogen atom.. Crcle the more acdc caton.. Crcle the more basc ntrogen atom. Students who have ther answers on ther personal workshop page and whose Unversty IDs end n the followng number should turn n ther sheets for extra credt!!! Whch has the followng compounds correctly classfed as, ant and non. 6 π-electrons 8 π-electrons 6 π-electrons ant non C D non non ant ant non ant

5 What s the correct classfcaton of cyclopentadene? ant. non C. π electrons cyclopentadene 6 π electrons ückel s Rule: If a cyclc π-system contans n + electrons t wll be stablzed by cyclc delocalzaton. 5