University:
Amherst College
Course:
CHEM 221 | Organic Chemistry I
Academic year:

2024
Views:

192

Pages:

3
Author:

Kathryn Duarte

Lecture outline Aromatic transition state theory provides a simple explanation for these results — A [1,5] shift of C — AO interaction diagram [1,5] X C Y Z C X A [1,3] shift of C — Y Z AO interaction diagram [1,3] X C Y Z and a classic experiment that confirmed the surprising prediction for the [1,3] C shift… D H H D H D or H D D H [3,3] sigmatropic shifts are also common — The Cope rearrangement and its oxygen-containing analog the Claisen rearrangement — O O These rearrangements normally proceed via a chair-cyclohexane-like transition state. When the chair is geometrically inaccessible, the reaction can proceed via a boat-like conformation, such as in the rearrangement of cis-1,2-divinylcyclopropane, which goes at a remarkably low temperature. < 0°C Note that many pericyclic reactions can be initiated by absorption of light rather than thermal energy. The "rules" for photochemical pericyclic reactions are generally the opposite of the rules for thermal reactions — reactions that are forbidden thermally are allowed photochemically and vice versa. We saw that the reason for this in cycloadditions was based on the π-MO interactions of an excited state reactant with a ground state reactant, but in general, a proper analysis of photochemical pericyclic processes is beyond the scope of this course. Here are some reactions that fall into the categories of cycloadditions, electrocyclic reactions, and sigmatropic shifts — a "1,3-dipolar cycloaddition" CO2CH3 N CO2CH3 N N N H2C CO2CH3 CO2CH3 Hint: think SN1 solvolysis — but what happens to the carbocation? EtOH OEt Br What kind of sigmatropic shift is this? < room temp Here's an enzyme-mediated Claisen rearrangement that plants use to synthesize phenylalanine and tyrosine… CO2– CO2– CO2– O O OH CO2– OH Phe, Tyr

Lecture Outline Aromatic Transition State Theory Provides a Simple Explanation For These Results

Related Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock