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Organic Chemistry – 1 st year Challenges in Chemistry Thomas B. Poulsen Challenges in Chemistry (CiC) Organic Chemistry Problems – 1st Year Students a) Reaction of 3,5,5-trimethyl-2-cyclohexen-1-one with NaNH2 (3 equiv.) in THF generates its enolate. When bromobenzene is added and stirred for 4 hours, the product below is generated in 30% yield. • Formulate a reaction mechanism (which of course involves drawing of the mentioned enolate and thereby also the structure of 3,5,5-trimethyl-2- cyclohexen-1-one). Hint: Reaction involves benzyne (read 16.7 in McMurry 9 th edition). b) When the material on the left is heated in acetone/water (80/20) it is converted to the material on the right: • Come up with a reaction mechanism that explains this rearrangement Hint: Reaction is related to nucleophilic substitution reactions. Read also 7.11 in McMurry. c) Bromination of the alkene to the left produces the product to the right: • Formulate a reaction mechanism which explains the formation of the specific stereoisomer shown. Try to rationalize your answer. • Provide systematic names for both compounds. Me HO Me Me O O Me Me O NO 2 NO 2 O O NO 2 NO 2 O Me Me Me Me Me Me H Me Me Me H Br 2 Br Me Br

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Page 1: Challenges in Chemistry - studerende.au.dk

OrganicChemistry–1styear ChallengesinChemistry ThomasB.Poulsen

Challenges in Chemistry (CiC) Organic Chemistry Problems – 1st Year Students

a)Reactionof3,5,5-trimethyl-2-cyclohexen-1-onewithNaNH2(3equiv.)inTHFgeneratesitsenolate.Whenbromobenzeneisaddedandstirredfor4hours,theproductbelowisgeneratedin30%yield.

• Formulateareactionmechanism(whichofcourseinvolvesdrawingofthementionedenolateandtherebyalsothestructureof3,5,5-trimethyl-2-cyclohexen-1-one).

Hint:Reactioninvolvesbenzyne(read16.7inMcMurry9thedition).b)Whenthematerialontheleftisheatedinacetone/water(80/20)itisconvertedtothematerialontheright:

• Comeupwithareactionmechanismthatexplainsthisrearrangement

Hint:Reactionisrelatedtonucleophilicsubstitutionreactions.Readalso7.11inMcMurry.c)Brominationofthealkenetotheleftproducestheproducttotheright:

• Formulateareactionmechanismwhichexplainstheformationofthespecificstereoisomershown.Trytorationalizeyouranswer.

• Providesystematicnamesforbothcompounds.

HOMe

MeMe

NO2

NO2O

NO2

NO2O

Me Me

MeMe

HMe

MeMe

Br2

Page 2: Challenges in Chemistry - studerende.au.dk

OrganicChemistry–1styear ChallengesinChemistry ThomasB.Poulsen

d)Thecompoundtotheleftisachiralmoleculecalledcamphenilone.Whenitistreatedunderratherextremeconditionsshownbelow,themoleculebecomesdeuteratedandatthesametimetheopticalactivityislost.

• Provideanexplanationforthisobservation.Hint:H-atomscanbeacidiceveniftheyarenotlocatedatothecarbonylgroupincaseothertypesofanion-stabilizationispossible.Drawthemoleculeindifferentways,lookforsymmetry.e) Solve NMR-problems 5, 6, 10, and 11 on the following pages. Provide concisedescriptionofhowyouarrivedatyouranswers (i.e. rationalize/deduce).Forproblem10,youneedtoknowtheexperimentcalledDEPT-135.Itsuseishoweverquitesimple:InaDEPT-135spectrummethyl(CH3)andmethyne(CH)carbonsareup.Methene(CH2)carbons are down. Quaternary carbons are not visible. You may also need to findexpected 1H and 13C chemical shifts for certain functionalities. These can be easilyfoundonline.Ifyougetstuckonanyoftheproblems,thencomeanddiscussthemwithme.

Furtherhintscanbeavailable.

MetBuOK

tBuOD, 185 oC

optically pureO

racemic