Chemistry 242-002. Organic Chemistry II with Professor Virgil Percec Tue. And Thu. 9:00 AM-10:30 AM. Calendar. Professor Virgil Percec E-mail: [email protected] Office: Vagelos Labs Room 4003 Office hours: T-Th 10:30 am - 12:30 pm or by appointment. Brad Rosen
Organic Chemistry II
with Professor Virgil Percec
Tue. And Thu. 9:00 AM-10:30 AM
Professor Virgil Percec
E-mail: [email protected]
Office: Vagelos Labs Room 4003
Office hours: T-Th 10:30 am - 12:30 pm or by appointment
E-mail: [email protected]
Office: Vagelos Labs Room 4080
Office Hours Thu Jan 17th and Tue Jan 24th 10:30 am – 12:30 pm
Class info on Blackboard: https://courseweb.upenn.edu/
Sign-up for Workshops: http://www.penntutoring.info/orgochem/
Please Direct all Questions Regarding Course Policy to Professor Percec
Lecture 1: Conjugated Unsaturated Systems
Chapter 13 in Solomons 9/e
Why Allyl versus Vinyl or Alkyl Substitution ?
Allylic Proton is easier to homolyze by 96 kJ/mol
Note: N-chloro-succinimide and N-iodo-succinimide exist and react in a similar way
1) The most important rule of resonance is that resonance structures are not real. They are merely a tool for rationalizing chemical behavior. We will revisit this in terms of the allylic and other conjugated systems.
2) In resonance we move only electrons, not atoms. And when we do it is usually π electrons.
Processes which involve “resonance” of atoms such as keto-enol
tautomerization (Chapter 17) are true chemical equilibria with where each
Isomer truely exists in solution
3) All resonance structures must be true Lewis Structures (Chapter 1.5)
4) Resonance structures must have the same
number of unpaired electrons.
5) Another very important rule is that systems in resonance need to be coplanar.
Butadiene is twisted out of plane
and is not in resonance
transoid 1,3 Butadiene coplanar
and in resonance
6) For reason which will be explained shortly, the energies of structures in resonance are always lower than those of their prototypical resonance forms.
7) Equivalent resonance structures make equivalent contributions to energies of the resonating compound
8) The more stable the resonance structure
the larger its contribution
One explanation for the peculiar stability of the Allyl Radical is through implications of resonance.
Indeed according to suggested stability via resonance , the allyl cation is unusually
AKA isolated dienes
A=ε x c x l = log (Io/I)
ε=extinction coefficient/molar absorptivity
l= path length
All π π* transitions
Expected Markovnikov Product
S-cis diene required,
s-trans does not work