Last Name. First Name. General Instructions: (i) Use scratch paper at back of exam to work out answers; final answers must

Transcription

1 Final Exam Chemistry 345 Professor Gellman 11 May 216 Last Name First Name General Instructions: (i) Use scratch paper at back of exam to work out answers; final answers must ff be recorded at the proper place on the exam itself for credit. Models are allowed. (ii) Print your name on each page. (iii) Please keep your paper covered and your eyes on your own work. r 1 - Misconduct will lead to failure in the course. e. d. I,..,.. 1. (32 points) Show the major product or products expected from each react;l. ~ 6r' (a) -1 ~ wr<>"a rv>+~+ i.c" ~v P'"'lu..c.tt.us -I ~r wa..inj,.,,/ "i\ CJ1~~ ~f ~; OCH3 1 equiv. Br 2 cat. FeBr 3 ~ I -... J L;:~ Oe«-!)...fo.- w rci ~ et~ --t u.'((? {tv\<:t.)i - ~) (c) G f~p~o J 11 ' ;1 ('~1C -r c±) (f\ki ~u 1' r<lj OU (d) (racemic) (\ACE,,M; (cont. on next page) -Z ~ ~r Shev.);nd S/-e,~ -Pn/'1 ~ri.t un+e.r /.9- f:r u~ J. i-1-cr ''~ -I -for e..:..c~ /11, rs/j >(6".t!..., ~c.. "ur{f) c -I] for TJ() s.,fekadi~j

2 1. (cont.) Name (e) ~_j H 6 Lccr/p~ ~ 3 ~r.c-th.t r o~] s-+e.r.e.c ~ms (f) OU OCH, 1) 2 equiv. CH 3 Li, THF 3) small amt HCI in H 2 (.J.) /~ L-1 ~~ ()'\\~) 2. (7 points) (a) Provide a mechanism (curved arrows) for the reaction shown below. OCH3 A B (b) The 1 H NMR spectrum of molecule B shown signals for 8 Hin the range In contrast, in the 1 H NMR spectrum of 1,3-cyclohexadiene (C below), the signals furthest to the left (farthest downfield) are for 4 H in the range Very briefly (no more than one sentence) explain why the signals for B are at larger 6 values relative to the signals for C. B JS

3 ,, ' Name (racemic) 4 (c) Br (racemic) 6

4 Name 4. (24 points) Provide a mechanism (curved arrows) for each reaction shown below. Draw all important resonance structures for intermediates. CN CN (cont. on next page)

5 Name 4. (cont.) (b) ~CN N_ao_H ~ v H2 I \ Cvr(~ ~(V ~.J, S(~ (fg f.,-/,, 11/\,i/ePfll~~rfe._ (~ ~v ~ ('R-s. s-lrvd) (f -f- foli) ' (cont. on next page)

6 {;..GJ 4. (cont.) :~ }- (c) r. '( u 5 ifoet 1) LiN(iPrh (1 equiv.) THF, -7aoc 2)Br~ Name ---- f 2 for ~1A fe'{. ~-((vq. e ~O'. / dl_og-1. o > r~ OE:-t

7 Name 5. (3 points) When the two molecules shown below are allowed to react under basic conditions, two products are formed, X and Y. The results of further reactions of X and Y are summarized below. Based on this information, provide structures for X, Y, X-1, X-2, Y-1 and Y-2 in the indicated boxes (next page). Your structures should be consistent with the IR data provided for each compound (only selected, strong IR signals indicated in each case). ~ ~ Na OH H3C x H + A x + v Ph~. H C CH H2, CH3H 3 3 (c.-tl,~1) (orl) X: 171 & 33 cm 1 Y: 1675 cm-1; no signal > 31 cm-1 X-1 and X-2 have very Cl (single CHO'' enantiomer) similar IR spectra, 3 CF3 with strong signals near pyridine X-1 + X & 174 cm-1; no signals > 31 cm-1 y Ph~. CHO'' 3 CF3 pyridine Cl (single enantiomer) No reaction y Y-1 Ph~. CHO'' 3 CF3 pyridine Cl (single enantiomer) No reaction Y-1: strong near 171 cm 1; no signal > 31 cm-1 y 1) LiAI H 4, Et2 Y-2 Y-2: strong signal near 33 cm-1 Ph~. CHO'' 3 CF3 pyridine Cl (single enantiomer) 2 products These two have very similar IR spectra; each has a strong signal near 174 cm-1 and no signals > 31 cm- 1. You do not have to draw these molecules.

8 Name _ 5. (cont.) x [NOTE: For the pairs X-1/X-2 and Y-1N-2, the order in which you draw them does not matter. Your job is to identify the two rrect structures.], ~, X-1-1u- Jxr~ fa--- ~ C UC113 \,.... <fj ~ l_ X-2 - l/1...j)-(r~ 'i c O(:JJJ Y-1 (rr )<-f ct- ;<.-8-. : -I ;f e_ ckj CO"'! f.j /5 I '116> ~ Y-2 Ott ~

9 6. (1 points) Name (a) Shown below is a drawing of the allyl radical. ~ Provide a drawing that shows the symmetry of the n molecular orbital that contains the unpaired electron (the "singly occupied molecular orbital", or SOMO). ~ 8 c_-c-c t). (t) (b) Shown below is an example of a [3,3]-sigmatropic rearrangement. The transition state can be considered in terms of interaction between two 3-carbon "fragments," each of which is an allylic radical. Provide a drawing to show how the SOMOs of two allylic radicals can be aligned so that both partial sigma bonds in the transition state (the sigma bond that is breaking and the sigma bond that is forming) correspond to bonding interactions in terms of n molecular orbital symmetry. This drawing should focus only on the n system, and not include any substituents.,, c orb,.j-af5 Ma:+ch fof -fl 9'Jed orb ift:t/5 fylo}ch up f Z Uo_ 5 node ~1 c.erd-r t:aj cct i{;:yi f 2

10 Name 7. (13 points) For each molecular drawing below, with reference to the H indicated by the arrow, label other H's as directed below. Put a CIRCLE around any homotopic H's. Put a TRIANGLE around any enantiotopic H's. Put a SQUARE around any diastereotopic H's. (J f. r 5Jf>lt,/. Y1 lri ff''j'n4e_ /1) e.:i<.c.e..f.\- -'-} CY\ ~~~ ( <}.)?Y"C +ti\'"\

11 8. (18 points) Name For each molecular drawing below, put a circle around SETS OF TWO OR MORE CARBON atoms that you expect to be NMR-equivalent to one another (achiral solvent). Designate sets of non-equivalent C atoms as 11 # , #2 11, etc., as illustrated in the example below (pentane). (Note: The numerical order (1, 2, etc.) does not matter.) If a carbon atom is unique relative to all other carbons in the molecule, then do not circle it. Example: Answer ' ~ (c) jf. j ~ ~ Br~Br --ij f :lid-_) (d) (-( f: r ~(;.,V\ ;-rre.4 'crje'')

12 9. (36 points) (a) Propose an efficient synthetic route from the indicated starting m erials to the target. ~ You may use any other starting materials containing 3 or fewer car ons, and any reagents~..: , zo Starting materials = Target = and AJ_OH (or : )V\ / fjrj or fe-//j<f) -- cont. on next page --

13 no 'i> ~s [) ~ i) ~"' t{j\.) bm.c- ~ fit.- 1-L ~., No.DJ.I M ~ H.. 111v hm.l s~'(/.ul drup~ C Ar cn.~ -/ r i(ln(;/. sou 1, ~ ""'11 7 a ~ u~f N1---=> /tjl-/2-, b ~ H J.IA! 1 bvj- Q"""' rk -Der N.-f-S r,;u..._

14 Name 9. (cont.) (b) Propose an efficient synthetic route from the indicated starting material to the target. You may use any other starting materials containing 3 or fewer carbons, and any reagents. Starting material = Cl~ ~CH 3 Target = Cl~ ~~ y.jj/rlvv7.,-j~ ' ej ) fl~ f,,}j -' A. J},<{JJ~ lj..f51oj /{<-<JI! (y; ~ C; y{jl-~y 2_{~4911/- z)~o - &"" 7 I c_ L""" ~' 1fl k /;.>JJ J '711'>1frtv cf!_. ~~~-t ~ =/.~