MIDTERM #3 PRACTICE TEST #1

Transcription

1 EM 234 PRITED FIRST AME the exam cover sheets look kind of like this PRITED LAST AME ASU ID or Posting ID Ian R. Gould Person on your LEFT (or Aisle) Person on your RIGT (or Aisle) PRIT YUR AME EA PAGE! READ TE DIRETIS AREFULLY! USE BLAK PAGES AS SRAT PAPER work on blank pages will not be graded... WRITE LEARLY! MLEULAR MDELS ARE ALLWED D T USE RED IK D'T EAT, USE MM SESE! Li Be B F e a Mg Extra redit /5 e Al Si P S l Ar K a Sc Ti V r Mn Fe o i u Zn Ga Ge As Se Kr Rb Sr Y Zr b Mo Tc Ru Rh Pd Ag d In Sn Sb Te I s Ba Lu f Ta W Re s Ir Pt Au g Tl Pb Bi Po At Rn amine alcohol (δ, ppm) small range range of values broad peak R 2 R R R 3300 variable and condition dependent, ca. 2-6 δ peaks Aromatic Ar mainly usually strong R R 2 R Xe Infrared orrelation hart Total (incl Extr / R Interaction Energies, kcal/mol Eclipsing / ~1.0 /Me ~1.4 Me/Me ~2.6 Me/Et ~ R broad with spikes ~ broad ~ R2 broad ~ (cm -1 ) MR orrelation harts TIS IS A M 234 PRATIE EXAM MIDTERM #3 PRATIE TEST # X R 2 R X Gauche Me/Me ~0.9 Et/Me ~0.95 i-pr/me ~1.1 t-bu/me ~2.7 Approximate oupling onstants, J (z), for 1 MR Spectra Alkyl 3 Y > 2 Y > 1 Y Alkyl ~2 ~10 ~ ~8 ~2 ~7 3 Y > 2 Y > 1 Y 0 0 Aromatic R 2

2 - 2 - EMISTRY 234, MIDTERM #3 PRATIE TEST #1 AME Question 1 Give the IUPA name for the following compounds. Be sure to use cis/trans, E/Z or R/S where appropriate. trans-(5r)-hydroxyhex-(3)-enal * R R 5 1 (5R)-hydroxyhex-(3E)-enal aldehyde not numbered, is in position #1 by definition Question 2 Rank in order of increasing equilibrium constant for formation of an acetal with a brief explanation. Draw the expected acetal for one of the reactions (only), it does not matter which one. A Me + (cat.) Me Me acetal B lowest < A < highest B Me + (cat.) Me Me acetal Me Me + (cat.) F F F F Me acetal Me is a weak L Base, reactivity of carbonyls (=) with Lewis bases depends upon substituents effects on the carbonyl carbon, B has two weakly donating alkyl groups attached to the carbon of the = and is thus the least reactive and has the smallest equilibrium constant, has 2 F atoms that inductively withdraw electrons and increase reactivity and equilibrium constant Question 3 Give the alkyl bromide and the carbonyl compound you would use to synthesize the following alkene in a Wittig synthesis and show all steps and reagents/conditions PPh 3 Ph 1 bromide preferred P 3 P Ph BuLi P 3 P + Ph Ph

3 EMISTRY 234, MIDTERM #3 PRATIE TEST #1-3 - AME Question 4 For each reaction Provide the missing reagents/conditions or major organic products as appropriate, pay attention to stereochemistry including racemic mixtures unless specified b) Unless otherwise indicated... State whether the VERALL reaction is Addition, Elimination, Substitution or Rearrangement State whether the reaction is oxidation, reduction or neither iefly explain whether the a solution of the product would be optically active or not Zn(g) l, 2 * * SUBSTITUTI (of 2x for 2x) REDUTI not optically active achioral meso compound b) 1 Equiv. ( 3 ) 2 l (cat.) ignore stereochemistry/optical activity ignore oxidation/reduction ignore addition/elimination etc Me 2 c) a 2 r 2 7 / 2 S 4 ignore stereochemistry/optical activity ignore addition/elimination etc. XIDATI d) /l All 3 ignore stereochemistry/optical activity ignore oxidation/reduction etc. SUBSTITUTI e) 3 + ignore stereochemistry/optical activity ignore oxidation/reduction ignore addition/elimination etc

4 EMISTRY 234, MIDTERM #3 PRATIE TEST #1-4 - AME Question 5 Draw the complete arrow pushing mechanism for the following reaction. Indicate the Lewis acid/base at each step, and if they are also ønsted acids bases. Add non-bonding electrons as necessary. Draw the ALL important resonance structure of the intermediates 3 LB/BB 2 3 LB LA 3 Ts (cat.) LB/BB 3 LA/BA LA/BA Ts LA/BA Ts 2 LB/BB 2 LB/BB 2 LA/BA 2 note: the order of the first 2 steps in mechanism could be reversed! Question 6 Rank the following in terms of increasing rate of reaction with PhMg. Give a BRIEF explanation and AME the three functional groups ketone WD WD A SD WD B WD = weakly donating SD = strongly donating ester WD B < A < this is reaction of a strong nucleophile/lb with a carbonyl = bond, which can be considered to be a small π-system, the carbonyl carbon in the ester B has a strong electron donating oxygen substituent on the carbonyl and a weak electrom donating methyl group, which decreases reactivity towards the LB/nucleophile, the ketone A has 2 weak alkyl donating substituents on the carbonyl carbon, the aldehyde has only 1 weak alkyl donating group aldehyde

5 EMISTRY 234, MIDTERM #3 PRATIE TEST #1-5 - AME Question 7 Show how you would make the target molecules from the provided starting structures. Show all intermediate structures, do not show any mechanisms / 2 S 4 1. KMn 4 / / heat separate isomers / Fe b) P 3 a/ 3 (l) l cat. a recall, 3 + does not react with alkynes without g 2+ as a catalyst

6 Question 2. For the onsted acid/base reaction below: Give the curved arrow-pushing in both directions b) Draw a reaction energy diagram and include a drawing of the transition state c) Label the acids/bases and which are stronger and give a brief explanation d) Indicate which reaction is faster (left to right or vica vers and on which side the equilibrium lies and which acid has the smaller and which the larger pka slower + + faster weaker base weaker acid stronger acid stronger base larger pka smaller pka equilibrium on TIS side energy reaction coordinate the weaker base has lower energy electrons because the ion is aromatic, the stronger base is anti-aromatic if flat, or it it twists it may become non-aromatic, but will be less stable than the aromatic anion in any geometry Question 5. The purpose of this question is to determine whether the provided product is allowed or forbidden Δ 1) draw the arrow-pushing that describes formation of the PRVIDED product 2) ow many electrons are involved in the reaction? 6 electrons 3) FR TE PRVIDED PRDUT (which may or may not be allowed), would the ring closing be disrotatory or conrotatory? onrotatory 4) FR TE PRVIDED PRDUT (which may or may not be allowed), would the transition state be ückel or Möbius? Möbius 5) Is PRVIDED PRDUT allowed or forbidden and why? Forbidden, the allowed product of a 6-electron electrocyclic ring closing reaction would proceed via an aromatic uckel transition state and would be disrotatory, not Mobius/conrotatory

7 EMISTRY 234, MIDTERM #3 PRATIE TEST #2 START F PRATIE TEST #2-2 - AME Question 1 Give the IUPA name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate hydroxy-4-methylhept-(4E)-en-6-ynal Question 2 Rank the following in terms of increasing rate of electrophilic aromatic substitution, e.g., reaction with 3 / 2 S 4. Give a BRIEF explanation W W D W D D D A D D B D D D A < B < the reaction is electrophilic aromatic substitution, as far as the central benzene rings are concerned, A has 2 D/activating groups and 2 W/deactivating groups, B has 3 D/activating groups and 1 W/deactivating group, has 4 D/activating groups, is thus fastest in electrophilic aromatic substitution Question 3 Give the product of complet acid catalyzed hydrolysis of the following structure 3 + add = here cleave the 2 single bonds indicated by the dashed lines

8 EMISTRY 234, MIDTERM #2 PRATIE TEST #2-3 - AME Question 4 For each reaction Provide the missing reagents/conditions or major organic products as appropriate, pay attention to stereochemistry including racemic mixtures unless specified 1. Ph-Mg b) Me All 1. 3 l 2. Zn/g/l/ 2 Me c) (±) hemiacetal formed with base d) ( 3 ) 2 Me 2 F 3 2 (TFA) cat. (or any other organic acid catalyst) e) 1. BuLi BuLi S S 4. Ph 2 Ph

9 EMISTRY 234, MIDTERM #3 PRATIE TEST #2-4 - AME Question 5 Give a full curved arrow-pushing mechanism for the following reactions, show where every proton goes to and comes from (no + + /- + ) and indicate the Lewis and onsted acids/bases at each intermolecular step, include important resonance contributors for all intermediates, give the number of steps in your mechanism. LB/BB LA/BA l/ 2 LB/BB LA/BA LA LB LA/BA LA/BA LB/BB SEVE steps b) LA/BA LB/BB a/ 2 LB/BB LA/BA

10 EMISTRY 234, MIDTERM #3 PRATIE TEST #2-4 - AME Question 6. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms. 2, hν Mg Mg. TF / + cat. (not 3 + ) ab 4 /Et /RR Mg.TF Mg

11 Question 6) The ylide below undergoes an electrocyclic ring closure reaction t-bu S t-bu Δ S t-bu t-bu * * meso compound give the curved arrow-pushing that accounts for product formation b) draw the product, paying special attention to relative stereochemistry of any substituents c) indicate the locations of any chiral (asymmetric) carbons atoms * with the * symbol, and state whether it is racemic, a meso compound or achiral d) give the UMBER of electrons involved in the reaction 4 e) state whether the allowed reaction proceeds via a uckel or a Mobius transition state Mobius f) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing conrotatory the reaction is antarafacial on the lower reactant because the cis-stereochemistry of the substituents becomes trans- in the product (this would not be included as part of the answer) Question 9) lassify the following structures as aromatic, non-aromatic or anti-aromatic, assume all structures are as flat as possible, AD give the number of electrons involved in the conjugated system sp3 4 electrons 4 electrons non-aromatic anti-aromatic anti-aromatic these electrons are in sp2 hybrid A.. 8 electrons anti-aromatic 8 electrons

12 EMISTRY 234, MIDTERM #3 PRATIE TEST #3 START F PRATIE TEST #3-2 - AME Question 1 Give the IUPA name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate R * (4R)-hydroxyoct-(6Z)-en-2-one Question 2. Give a complete curved arrow pushing mechanism, and... 1) Indicate the Lewis acid/lewis base (LA, LB) at each step as appropriate, and whether they are also ønsted acids/bases (LA/BA, LB,BB), show where every proton comes from and goes to (no + + /- + ) 2) GIVE TE UMBER F STEPS I YUR MEAISM l l l FUR steps Question 3) lassify the following structures as aromatic, non-aromatic or anti-aromatic, assume all structures are as flat as possible, AD give the number of electrons involved in the conjugated system sp3 6 electrons aromatic non-aromatic 6 electrons these electrons are in sp2 hybrid A..s aromatic 6 electrons

13 EMISTRY 234, MIDTERM #3 PRATIE TEST #3-3 - AME Question 3 For each reaction 1) Provide the missing reagents/conditions or major organic products as appropriate 3 + Ph 3 Ph b) /l All 3 and/or c) Ph Mg 3 + Ph d) 1. PPh 3 2. BuLi 3. e) ignore stereochemistry 1 Equiv Ḣ Ts (cat.)

14 EMISTRY 234, MIDTERM #3 PRATIE TEST #3-4 - AME Question 4 Rank the following in terms of increasing frequency of carbonyl stretching vibration in an IR spectrum. To solve this problem you will ened to draw minor resonance contributors and remember that stronger bonds vibrate with higher frequency) the more the minor resonance structure contributes to the overall structure, the more the = bond has single bond character, the lower the vibrational frequency... 3 A 3 Me 2 B B < < A is not a donor, does not stabilize the minor resonance structure which is thus a small contributor to the structure 3 Me 2 3 Me 2 -Me 2 is the strongest donor, it stabilizes the minor structure resulting in a largest contribution to the structure of these three 3 3 -= 2 is a weak donor, it is in the middle Question 5 Give the product of the following reaction. Remember that D represents deuterium, an isotope of hydrogen, that is used to keep track of where hydrogen atoms go in chemical reactions. We did not cover this reaction class, but you should be able to work it out based on what you know about the mechanisms of these reduction reactions 3 1. LiAl D 3 + D 3 3 Question 9) The structure below undergoes an electrocyclic ring opening reaction (remember, D means deuterium, an isotope of hydrogen that is often used as a labelled hydrogen atom) D D Δ D give the curved arrow-pushing that accounts for product formation b) draw the product, paying special attention to relative stereochemistry of any substituents c) give the UMBER of electrons involved in the reaction 6 d) state whether the allowed reaction proceeds via a uckel or a Mobius transition state uckel e) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing disrotatory D

15 EMISTRY 234, MIDTERM #3 PRATIE TEST #3-5 - AME Question 6. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms. 2 S 3 KMn 4 boil 2 Fe S 3 2 S 4 S 3 b) l cat. 2 /Pd/ Mg.TF 3 + Mg Mg

16 EMISTRY 234, MIDTERM #3 PRATIE TEST # AME Question 7 Give a full curved arrow-pushing mechanism for the following reactions, show where every proton goes to and comes from (no + + /- + ) and indicate the Lewis and onsted acids/bases at each intermolecular step, include important resonance contributors for all intermediates, give the number of steps in your mechanism cytosine is one of the pyrimidine bases in DA, it can be converted into uracil. if this happens this can be a damage mechanism that could lead to mutation. Assume that this reaction occurs via the usual acid catalyzed mechanisms that we study in class, give a mechanism for formation of uracil from teh provided tautomer of cytosine b) cytosine tautomer 3 + uracil + 3

17 EMISTRY 234, MIDTERM #3 PRATIE TEST #4 START F PRATIE TEST #4-2 - AME Question 1 Give the IUPA name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate butyl-4-methyl-5-oxo-hex-(3E)-enal Question 2 Rank the following in order of increasing equilibrium constant for formation of a hydrate. Give a BRIEF explanation 3 A 2 B δ- δ+ A < < B the reaction is addition of a weak nucleophile to the = group, A is least reactive since it has a strong donating group that can stabilize the carbonyl carbon via resonance, B has a withdrawing group that destabilizes the carbonyl carbon Question 3. Rank in order of increasing rate of reaction with, give a BRIEF explanation A B F F (fastest) < A < B (slowest) B has donating group (oxygen) adjacent to the =, decreases reactivity towards nucleophilic attack, has two electronegative groups adjacent to the =, inceasing reactivity towards nucleophilic attack

18 EMISTRY 234, MIDTERM #3 PRATIE TEST #4-3 - AME Question 4. For each reaction. 1) Provide the missing reagents/conditions or major organic products as appropriate 2) Pay attention to stereochemistry including racemic mixtures unless specified 2 l (cat.) 2 4 b) K/heat 2 / Fe c) F 3 F 3 d) ( 3 ) 2 + cat. enamine e) 3 +

19 EMISTRY 234, MIDTERM #3 PRATIE TEST #4-4 - AME Question 5. Show how you would synthesize the target compound on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms. l l / All 3 2 l 2 / Allr 3 3 / 2 S 4 bit of a trick here, the lemmensen reduction would probably also reduce the - 2 to the required - 2 making the next step ( 2 /Pd/) unnecessary, but you would not lose points for the separate reduction of the Zn(g)/l/ 2 2 /Pd/ 2 / Fe 3 separate isomers 2 2 b) 2 Ph 1 Equiv l cat. 3 2 l (cat.) 1. PhMg Ph

20 EMISTRY 234, MIDTERM #3 PRATIE TEST #4-5 - AME Question 6 Give a full curved arrow-pushing mechanism for the following reactions, show where every proton goes to and comes from (no + + /- + ) and indicate the Lewis and onsted acids/bases at each intermolecular step, include important resonance contributors for all intermediates, give the number of steps in your mechanism b)

21 EMISTRY 234, MIDTERM #3 PRATIE TEST #4-6 - AME Question 7 Rank in order of increasing rate of reaction with a Grignard reagent, giove a brief explanation in terms of nucleophiles and electrophile stregth and tthe factors that control these in this context. 3 F A B D < A < B < D In these reactions the Grignard is the Lewis base and the carbonyls are the Lewis acid, the stronger the Lewis acid the faster the reaction the carbonyl carbon in D has two weak donating -3 groups attached, which decerases the electrophilicity, this reaction is slower than A (one donating group) which is slower than B (zero donating groups) is fastest of all, the -F3 is electron withdrawing, which incerases the electrophilicity of the carbonyl carbon Question 8. Rank in order of increasing rate of electrophilic aromatic substitution at the carbons indicated by the arrows. Give a BRIEF explanation. B A D 3 D < B < < A slowest fastest Reaction at both A and is faster than at B and D, because both are activated by strong (amine) and weak (aryl) donating groups on the ring. Reaction at A is activated more than at because the strongest donating group activates more. Reaction at B and D is deactivated by the by strongly withdrawing nitrile group, but D is deactivated more than at.