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Reflection 1c: Content Enduring Understandings C


Enduring Understanding C: Chem503: Organic Chemistry II (Fall 2007/ Spring 2008)
Aldehydes & Ketones: The polarity of the carbonyl group activates it toward reaction with Lewis acids and Lewis bases.
Enols & Enolates: The reaction of enolates with electrophiles is one of the fundamentally important reactions for forming carbon-carbon bonds/ The aldol condensation is an especially useful reaction for building up more complex carbon skeletons from simpler ones.
WHAT is the evidence? WHY did I choose this evidence?  HOW does the evidence show growth?

I chose to show my growth in my understanding of organic chemistry, specifically carbonyl and enolate chemistry, by comparing an old undergraduate exam question on which I had received zero credit (my baseline) with an MCE exam question on which I received full credit (my later evidence).  To further demonstrate my deeper understanding of this fundamental category of organic chemistry, I also correctly re-answered the old exam question using my improved understanding of enolate chemistry (and nucleophiles and electrophiles). 

I chose to document the growth in my understanding of carbonyl reactivity because it is a foundational concept in Organic Chemistry and because my improved ability to understand the patterns or logic behind this one topic is indicative of the significant growth in understanding I've experienced in many other areas of Organic Chemistry as a result of Dr. Robert's instruction and masterful use of POGILs (all hail the POGIL-master...). 

Please see below each piece of evidence for a more detailed discussion of related content.   You may click on any piece of evidence for a larger image.

Baseline Evidence (click on pic for larger image)
Undergraduate Organic Chemistry Exam Question from February 2001
 Later Evidence (click on pics for larger image)
baseline enone exam question

The baseline evidence shows that I did not have a true understanding of the enone-enolate resonance that affects an enone (a conjugated alkene/ ketone)'s reactivity.  Analysis of my baseline shows my lack of understanding because I have the oxygen's lone pairs and the double bond electrons moving in opposite directions, in a non-concerted manner, a mechanism step that is illogical and shows a poor grasp of the enone's unique pi conjugation.  I also have an unstable primary carbocation and several unstable charges throughout the mechanism.

 Evidence #1: MCE Organic Chemistry Exam Question from November 2007
later enone exam question

In comparison, the exam question above shows my understanding of how a carbonyl group makes the hydrogens on an alpha carbon of the ketone acidic.  When a hydrogen is removed from the alpha carbon with the catalytic addition of a base, the e- can form an enolate ion which is resonance stabilized:
enolate ion
This enolate ion makes the double bond electron pair extremely nucleophilic, and thus, it will attack nearby carbonyl groups.  The carbons of carbonyl groups are electrophilic due to the electron withdrawing effects of the electronegative oxygen. 

The negatively charged oxygen of the former carbonyl group then grabs a hydrogen from water, forming a hydroxyl group (an alcohol).  An aldol condensation then occurs as a base attacks the acidic hydrogen of the alpha carbon, simultaneously producing electrons that form the double bond of a resonance stabilized enone and eliminating the hydroxy group.
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Evidence #2: Answer to baseline exam question (June 2009)
answer to baseline exam question

In my second piece of later evidence, I further prove my growth in understanding of carbonyl and enone/ enolate chemistry by reanswering the original baseline exam question and providing a plausible mechanism for the reaction of a ketone (an enone) with a sulfur ylid to produce a cyclopropane. 

Because of the resonance of the enone, the beta carbon is a favorable site for nucleophilic attack by the sulfur ylid (which is a strong nucleophile because of the carbanion).  The double bond electrons of the enolate ion then nucleophilically attack the electrophilic carbon attached to the positive sulfur ylid.  This produces a cyclopropane and a stable sulfur compound.
Updated June 28, 2009