CHEM 2332H Lecture Notes - Lecture 12: Electrophile
15 Jul 2014
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Assumption: molecule is flat (flat conformation) -->p orbitals are all sticking up/down so they can find each other and overlap constructively (couldn"t overlap if perpendicular) Can rotate about single bond and every 180 degrees, get p orbitals overlapping, but while rotating, goes through some points where p orbitals are perpendicular to each other. s-cis +. 28 kcals (p orbitals overlap b/c steric hindrance) 90o ~ 7 kcals b/c now you lose 1st lowest energy bonding mo b/c p orbitals don"t overlap at all. Allyl mo: has 3 c"s, 3 p orbitals [c3h5]+/. /- (can be cation, radical, or anion) Here, node comes on middle c (on dashed line) so 0 chance of electron being there. Allyl cation is an electrophile: the electrophilic portion of a molecule/ion is best described by lowest. Unoccupied molecular orbital (lumo): has lobes in that mo, no nodes; it"s the first one cation doesn"t fill (in this case, pi2); can see the 2 lobes.
