HT3ans-06.cwk - Answers to Hour Examination#3 Chemistry...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Answers to Hour Examination #3, Chemistry 302X, 2006 1. (a). That S N 2 shown just can t happen with the required inversion. The “back” of that methyl group is not reachable by the putative nucleophile, the pi system of the enolate. (b). Although displacement of the methyl can t happen, addition to the ester carbonyl can. So, one mechanism begins with the addition of the ketone enolate to the ester carbonyl to give A , then, perhaps, the symmetrical intermediate B . O CH 3 O OEt OEt O O CH 3 B O O CH 3 1 A Intermediate B can undergo addition of ethoxide to either carbonyl (right-hand reverse arrow above) to regenerate A and go on to products shown below. Even better (probably) would be the direct opening of the initial adduct A to give an enolate that protonates to product. OEt O O CH 3 OEt O O CH 3 CH 3 O EtOOC A
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Alternatively (and better) we could do the other archetypal reaction of carbonyl groups and add alkoxide to the ketone C=O. A reverse Claisen, followed by a forward Claisen, leads to enolate C . A final protonation gives the product. RO RO O COOEt CH 3 O COOEt CH 3 H O COOEt CH 3 H 3 O + C OR COOEt CH 3 O O COOEt CH 3 OR O COOEt CH 3 O CH 3 OR O OR O COOEt CH 3 OR protonate deprotonate now salt formation is possible: (–) (–) (c). Now, how to tell them apart? Label one (either) carbonyl group. Here are the three possibilities, starting with labelled ketone: Direct opening of A gives product labelled as in D : OEt O O CH 3 OEt O O CH 3 CH 3 O EtOOC A D If the symmetrical intermediate is formed, there must be 50% of 4 produced with the other 50% in the ester carbonyl.
Image of page 2
The reverse Claisen puts the label completely in the final ester product.:
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern