{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Organic Chemistry 2 - ANSWERS.MID 09

Organic Chemistry 2 - ANSWERS.MID 09 - C HM 21 20 MI DTER M...

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

View Full Document Right Arrow Icon
CHM 2120 MIDTERM EXAMINATION OCTOBER 17, 2009 TIME: 2H TONY DURST __ANSWERS AND MARKING SCHEME Please Note: 1. The total marks for the exam is 75 points. The marking scheme is a guide and should be considered approximate. It is subject to small changes 2. Answer all questions. Read the questions carefully and answer what is asked. 3. Part marks are given for reasonable, but incomplete answers. Question 1. 6 points Name each of the following structures using either the IUPAC system or an acceptable trivial name OR supply a structure to a name. Stereochemistry, if shown, should be recognized either in the name or in the structure drawn. H F H CH 3 a) b) CO 2 H H 3 C H 3 C c) (E, Z)- 2,4-hexadiene d) para-nitrophenol e) the allyl carbocation e) OH Cl MARKING; 1 POINT FOR A CORRECT UNAMBIGUOUS ANSWER. 0.5 POINTS[ one time only] for an answer that has a minor flaw. The TA marking this made the choice and was consistent. The answers shown are acceptable answers. Others may also be OK but they must follw one of the acceptable systems and be unambiguous (Z)-1-fluoro-1-butene 3,4-dimethylbenzoic acid. the numbering can be clowise or counterclockwise to get the smallest numbers.. The carboxyl carbon must be #1. H 3 C H CH 3 H OH O 2 N H H (+) In th end we accepted any allyl cation trans-2-chloro-cyclohexanol remeber E and Z are used in alkenes. cis and trans are use to define stereochemistry rings in
Image of page 1

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

View Full Document Right Arrow Icon
Question 2. 7 points MARKING. ZERO POINTS FOR GUESSES RE THE DIRECTION. 2 POINTS FOR A RESAONABLE JUSTIFICATION. Part marls were considered, but not if the answer had serious flaws. Indicate the direction of the equilibrium in each of the following and EXPLAIN the reason for your choice. H 3 C N + a) CH 3 CH 3 H (+) OH H 3 C N CH 3 CH 3 O H H (+) + Left. Quite strongly. The simple reason is that a protonated alcohol is much more acidic than a protonated amine. Nitrogen carries a positive charge much more readily than oxygen due to its lower electronegativity. OR: amines, for example ammonia are stronger bases than alcohols and water. Thus you can easily conclude Weaker acid weaker base stronger base stronger acid. **************************** C C H H 3 C + Na (+) (-) OtBu C C (-) Na(+) H 3 C + HOtBu b) Strongly left. Again electronegativity gives the easy answer: Carbon is much less electronegative than oxygen therefore an a carbon anion R3C(-) will be less stable than an RO(-). Or You could have quoted pKa values: the terminal acetylene has a pKa of 25 and the tert-butanol has a pKa of 19. Thus the alcohol is the stronger acid. Many of you remembered that t-butoxide is a very strong hindered base. It is the strongest of the RO(-) bases but not strong enough to deprotonate a terminal alkyne. Weaker acid weaker base stronger base stronger acid. ****************************** H 3 C (+) H 3 C (+) CH 3 CH 3 A B c) H 3 C (+) CH 3 Right. The carbocation on the left is tertiary: the one on the right is tertiary and allylic and therefore resonance stabilized. Another way of answering would have been to draw the resonance for B. [shown in the box]
Image of page 2
c-1) Show also the mechanism for the conversion of A to B or vise-versa.
Image of page 3

Info icon This 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