Solns2-03-06

Solns2-03-06 - CHEM 252: HONORS ORGANIC CHEMISTRY ll Spring...

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Unformatted text preview: CHEM 252: HONORS ORGANIC CHEMISTRY ll Spring 2006 Dr. David J. Lapinsky 2 / 3 / 06 Problem Session: Conjugation and Aromaticity 1.) Compounds 1 - 3 are structurally similar, yet one of them is much more acidic than the others. Identify the most acidic compound from the illustrated set and provide an explanation for its exceptionally high acidity. 2.) True or False: The same anion is formed by loss of the most acidic proton from 1-methyl-1,3-cyclopentadiene as from 5-methyl-1,3-cyclopentadiene. Explain. 3.) One of the compounds pictured below is very stable. However, the other compound is quite unstable and rapidly undergoes a Diels-Alder reaction with itself. Provide an explanation for the different stabilities of these two compounds and draw the expected Diels-Alder adduct from reaction of the unstable compound. 0 0 d7 4.) The following conjugated polyenes have very different reactivity profiles. Draw electron pushing mechanisms in order to predict the products of the following reactions. (Note: for 1,3,5-cycloheptatriene, a 1,6-dibromide adduct has been observed followed by loss of HBr ) O Brz 999 '—'———> . . . s V . Br2 —--——> 7?? 5.) Which of the following species are expected to be aromatic? You must defend your answer (perhaps practice some Frost circles). 6.) Thymine is one of the four bases of DNA and it can exist in four tautomeric forms (one keto, two enol, and one dienol forms), one of which is shown below. Draw the other three tautomers and indicate which of these, if any, are aromatic. Once you have all the tautomers drawn, propose electron pushing mechanisms for their interconversion under... - catalytic acid conditions - catalytic base conditions HN ' 0% N H 7.) Suggest efificient ways to carry out the following transformations. Assume you have access to any organic or inorganic reagents you need unless otherwise noted. 7a.) / ??? 7b.) ©/\ ??? O OH (only source of carbon atoms) 7c. ) ¢ ??? OH Br 7d.) 7?? (racemic) 8.) The Birch reduction can be regioselective depending on the electronic nature of the substituent on the benzene ring. (Note: electron-donating groups (EDG) can be readily identifiable via the atom directly attached to the benzene ring possessing a set of lone pair electrons that can donate into the benzene ring via resonance) EDG éDG Na, NH3 -- “._tl~Te—n——‘> EDG = -OMe, -NR2, -ha|ogens, etc. ROH VS. EWG EWG Na, NH3 ————Th—efi——> EWG = -N02, -con. -CN, etc. ROH Consider the mechanism of the Birch reduction and electronic effects in order to provide an explanation for the observed regiochemistry of the Birch reduction. 9.) The Birch reduction was influential in the synthesis of norethindrone, a progesterone that was a component of the first effective oral contraceptive (i.e. birth control pills). The methodology below was used by Carl Djerassi (Stanford University) to synthesize norethindrone and he is considered to be “the father of the pill”. - Provide the structures of intermediates A and B given that B is driven by thermodynamic stability and the regioselective nature of the Birch reduction (question #8). - Propose an electron pushing mechanism for the conversion of B to C. Any thought as to what is driving this particular transformation? 71‘ Mel H30+ H‘s-k KCO H 0 £1 ——»2 a A we HO 9" ROH 0 a" c Norethlndrone Sohfiioo; 1 3/5106, ® .— $ fie) (5-H Y : u/V H .J -> 1 \ x a '6 : fired 2‘ H :6 (AROMM \c_\ r r A immune and {H mm Aid.” 1 x/ * Cans. ‘Oaae 5%a\;\‘22.(} by (a: ‘7 5*r0P-q chimth cg” {1‘ ~ 6 Cflmea {/ _ quavgn’mfiene ® /5—me7\\\\f\‘ \3 za’QYc.\QFQn“Qo\;Qn€ @ l‘mafl‘ny\ ‘ 1:1; 6) ‘— 4Brw1t-A clqu Lon “:6 /‘7 H - E; L ’“ U ’ ram: 1 AZIQL“.OA A, H (5—H ‘ "" "w‘... V w n_ .. w~ u ~-~m~ w vim-n x "W" “ ""“" n v ‘ u‘ ‘ --——._..__.._.,_.._.——-—. mm‘wqwmr‘m .‘ NW“; .4 .‘ -MN\ 8 © ' 31x63 U l 1 ’ Hues M J “61f C‘(Dl\a“‘.<_‘ n'u M r ( VC- 0 a W \u co 3 afi On Q cafe my» Q Hud‘c\ M n * H \w- I no" Qfomakfg V‘c‘ 4 \Ofiefi} H c‘MJfi ~ 9 axomq‘LQ 2Q HULKJ 3* <+‘r\"g 15 'fl {5-H / H ,\ N/ N \N‘« ‘ fig )\ l .1... / \ VJ N )\ O 'TI gt“ ——-——--———--—-W__..__—.._. _._—___ M r N65 Pk W 5r /W “"‘""'"7 Pk cow P \ (0' sh fir 8r ‘rw +O\< (“A +OH I} @A-\¢g~\w\* Jm “the. 1m ‘ - H O C : resioq‘othfl'rj of “Us 3_ x / Die.\s A\de_r "'\°\ \ A \ :Azg*<onic$ 3 e¢(kfles E a Q39\) Pk m P“ ® S“‘QJ; Q3 VHL \IVQ nnfi'scl Rem. ® 9" N63 +QK \ mQPEA '0 __,__.————--—7 /\ CIA“ a, Pk +0H Pk ' “‘4! PhN k. (E33) ® EAAQ mafir ® “a k Pk Ph 'len P W H0 OH 69 H} o 7 Br .- H6 Pk «4 "7 Pk N Pk /<l r Pb /\VOH LU‘AH“ “Mu-u» - M”_~m“m--Ww;m—mmuu~m “MM‘W_WM_WMMMWWM‘ ll NE$ /\ ___,___..——-————-7 ‘- M Pk CHE) CCJ ’7 Pk Br 6'6, \ h w L‘ :fl \ hem. X343 ) Lincflar ._———\ m Ph ~———\——_/—-— mCPEA —’ A] D (fa-LQM‘ ¢\ r:— n- (,E\ (“Ankh .fia (6:10 1-“ E06 306 Egg ® . NaNH; OW. No‘ @N‘ *‘fi\§ ungfiuosakflfi FLA "IL Cze- in*€,‘<.<.'\\on \ 1 V——-———— M he: sxvfiq‘ef,‘:d e, ‘ . ( Wk “\9— finck C)?“ H'NH& ‘C° “ A 1 Mb“\ 1 ‘ H—NH‘B‘ U (Q3 "‘ U rm {o'xov “w I! “(mat/fl \gdkw ‘1 EDC, \ (.3 (FHNOR, (CAREY )Q'\‘r\a QdAVLC’" ‘3‘: *he a .. . Q " E09 E09 "0 EGG NAN“; q)NfiE G Nana}. Na. WV,» ~ \ .[/ .\ 6?. \ (a re \ . *1; 6/» Vb \ '©®Na / \‘ C N; \ (mama , H-NH H‘NHN _ V\ w' Quo§A< U A (‘3 v 5 Eq“\“ _ ~ hne. r.o'\1d ® in+£<c1€hon bh'w «Await “son Jooné-mq 635*; -——.«- , “M ____m VS' Ewe ("COR Q: can mama» MK" R P\ /0 W‘Nq o 3f®fiq S, ‘I'K‘\;\l-\A {s «Camsdfle v 4 / ‘ r \ \ c .. V ‘_ Ho '\\nU a ( : ) E “‘1 '3 @ +=.'\(asu‘nsh*u‘\id "‘"m ‘1‘“ g P(OP°“C§ Ngr‘ran SM 5’ H O FISH; H30 M r My Mao H * "Hm, (fined a\Ke.ne Unmanzgivun xx“ 2 \S etabahhf dduen by “RE \ ®\§7 H O . » .. Ermq‘Ykon Q‘F q cons “aqk‘td H < aw; r. S\{s ham ~ ,J HAD-n) ...
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Solns2-03-06 - CHEM 252: HONORS ORGANIC CHEMISTRY ll Spring...

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