ANSWERS TO REVIEW PROBLEM SET CH F

Transcription

1 ANSWERS T REVIEW PRBLEM SET C41-018F [1] () The chirl isomer is stilized y intrmoleculr hydrogen onding etween the two guche groups. Such n rrngement lso keeps the ulky tert-utyl groups frther prt s they re nti to ech other. In the meso isomer, however, putting the two groups guche to ech other lso results in the tert-utyl groups ecoming involved in stericlly unfvorle guche interctions uch! C(C 3 ) 3 C(C 3 ) 3 Chirl isomer C(C 3 ) 3 () Note tht the two different strting mterils give the sme resonnce-stilized croction in this S N1 rection. Since oth lcohols, X md Y, re formed from the sme ction they will e produced in the sme rtio. It is ll right if you designted X nd Y differently s is does not ffect the nswer. C(C 3 ) 3 Meso isomer A - - X B - - Y (c) The two products nd their opticl ctivities re shown elow. ( 3 C) 3 C K ( 3 C) 3 C C C 3 pticlly ctive C C 3 C C 3 pticlly inctive pticlly ctive (d) The numer of signls in the C NMR would e different for ech compound. 13 c c c c d d c c c e d d c Three kinds of crons Five kinds of crons Four kinds of crons

2 (e) Note tht you need to do two hydroortion steps. The second one is intrmoleculr. 3 C B B C 3 B C 3 which is the sme s B C 3 (f) There is no chnge in dipole moment when the the doule ond strtches s it is symmetric so the C=C stretching frequency will not e visile in the IR spectrum. [] () Plese note how the nswer ddresses the regiochemicl nd stereochemicl nunces of the prolem. The finl product will, of course, e rcemic. C 3 C 3 C 3 1. B 3 Ts Ts N. / pyridine DMF Adding to 3-methylcyclohexene, however, would led to nsty mixture of products thnks to Witch s ew of croction intermedites. 1,-hydride shift mixture of stereoisomers mixture of stereoisomers () Some ides re given elow. ther pproches re lso e possile. 1. Mg. D D 1. B 3. /N 1. N C 3. C 3 I S

3 [3] () The tertiry chloride X is formed y the usul "Mrkovnikov" type of ddition tht involves the more stle tertiry croction. _ X () Bonds roken re worth out 169 kcl/mol (66 for C=C nd 103 for -). Bonds formed re worth out -184 kcl/mol (-99 for C- nd -85 for C-). So the rection is exothermic y pproximtely 15 kcl/mol. (c) See elow. Key to revitions re given t the ottom of the digrm. TS 1 D D I D 1 R D rxn Rection TS Progress R = 1-methylcyclohexene nd ; I = croction nd chloride; P = 1-chloro-1- methylcyclohexne (X); The ctivtion rriers for the first nd second steps re D 1 nd D respectively. TS 1 nd TS re the trnsition sttes for steps 1 nd respectively. The difference in enthlpy of product nd rectnts is D rxn. P (d) (e) The strongly electron withdrwing CF 3 group would destilize n djcent ction. So, in this cse, secondry croction is formed. As Y nd Z re oth chirl, ech of them will e formed s mixture of entiomers. F 3 C F 3 C _ F 3 C Y F 3 C Z

4 [4] In this cse, the 1,- nd 1,4- ddition of led to the sme product. 1,-ddition sme!! 1,4-ddition If we use D, insted of, we cn tell etween the two mechnisms ecuse the products would e different. D D D [5] Plese look up frgmenttion ptterns of ketones discussed in clss nd in your text. 70 ev - C 3 m/z = 71 m/z = 86 - C 3 C C m/z = 43 - C =C McLfferty m/z = 58 [6] The rection gives four products s shown elow. A B C D () S

5 () (c) A, B, nd C re chirl. A nd B hve plne of symmetry tht goes through the two romine toms. C, meso compound, hs plne of symmetry tht goes etween the two romine toms. D is chirl. (d) A nd B re distereomers, s re C nd D. Also, oth A nd B re structurl isomers of C nd D. [7] See elow. A B C D (c) 3 C C () () C 3 C C 3 () c

6 c (d) 3 C C (c) () C () C 3 d C 3 () [8] () The key step here is the rerrngement of the initilly formed croction to more stle 3 croction () Protontion followed y n intrmoleculr cycliztion develops the five-memered ring skeleton. Susequently, deprotontion occurs from two different sites to give the two products. Plese show rrow formlism for the deprotontion step... Deprotonte Deprotonte

7 (c) Be sure to understnd why the initilly formed ction undergoes rerrngement. () 1,-hydride shift _ resonnce stilized ction _ (d) To get this prolem right, you need to notice the presence of nitrogen which cn ct s n internl nucleophile to displce the chloride.

8 C41F18 puzzle Techer: Ds Thmttoor 1 C W 3 A T E R C P S M A L L E N E R R I C A I R T W 13 R F M 14 A N N E E R B R P X G C M S P L A R E P I R A E 0 C R M A 1 T G R A P Y B R K 3 E 4 A R L M T C P 5 6 T I L E Z E R 7 I C U P L I N G C N S T A N T N X L N T I C N L I K E E C E D 3 I T A N T 33 I P E R I P L A N A R E 35 S Y N R I R L R D I P L E D U B R A N 39 E E N N G R I G N A 4 R D V I N V E R S I N D I E N I 45 D E S Y S L C L C K W I S E A L C L U K T N B I I P T R A N 51 5 S S U N 53 R E N E W M A N L N I T E 57 A I R S S T A C N R T L M T C M B A S E G A C I D 60 I N T E G R A L S L T C 6 T L C R L D I A S T E R E M E R S

9 Across Alcohols tend to lose this in mss spectrometer This hs two djcent doule onds Preferred cyclohexne conformtion Numer of signls in the cron NMR of,3- dimethyl--utene Elimintion tht leds to more stle lkene This instrument seprtes the compounds in your smple nd determines their msses These compounds trvel slowly down silic gel column Technique of seprting compounds When ond it sored energy pticl rottion of rcemic mixture Cn e used to tell etween E nd Z isomers y NMR All in row Like dissolves Fvorle orienttion for E ydroortion involves this type of ddition Virtions tht don't chnge this re not visile in the IR Boron regent rgnomgnesium regent Stereochemicl outcome of n SN rection The strongest hydrohlic cid (lso doule s greeting) Groups with priorities 1,, nd 3 go this wy in n R stereocenter. A protic solvent You cnnot put this doule ond in smll ring Nturl source of photons This projection helps visulize eclipsed nd stggered conformtions rgnometllic regents re sensitive to this An lkoxide is good Accepts electrons The rtio of protons cusing signls in the NMR cn otined from these. This involves spotting plte These stereoisomers re not mirror imges of ech other Down E1 nd SN1 hve this in common ne might give this nd leg to do well in the chem finl This could e degree of unsturtion An ldehyde group Wht you turn in efore l. This hs four different groups on it A tertiry ction is stle thn secondry ction Generic lcohol Lrger groups void this position on cyclohexne An ether Scle of NMR spectr These re in the sme group Another nme for positively chrged. Two neighors might give this Product of lkene rection with percid s symmetry despite hving stereocenters An sp cron This hs two common isotopes in 3:1 rtio When two identicl groups re on the sme side Does not mix with wter This group shows nd round 1700 cm-1 A good leving group nd nucleophile Moleculr re formed when the smple is omrded y high energy electrons. SN1 nd E1 rections re moleculr Some Chem prolems re The trnsition stte of this rection resemles product Allyl ctions re stilized y this. The rte of n SN1 rection depends on this Not superimposle on its mirror imge This spect of rection is determined y the ctivtion rrier This tringle helps nlyze NMR splitting ptterns. This ond is usully sigm. A compound of the type RCR Good plce to do Chem reserch 57 NMR reference compound