Ch 11 HW Set: Substitution and Elimination

CHEM24

Dr. Spence

Ch 11 HW Set: Substitutionand Elimination

Substitution vs Elimination: Ask the following questions (1) is the substrate(R-LG) stericallyhindered? (2) is the nucleophilehindered?(all 3oandsome2oarehindered) (3) is the nucleophilea strongbase?

If the answerto any 2 of theseis yes,then elimination will be favored. If the answerto any 2 of theseis no, then substitutionwill be favored (and obviously if all threeansweryes : elimination). The next obstacleto determine(onceyou know what reactionwill occur) is what mechanismis in operation.

Sul vs SNZ

SNl : 3osubstrate(or 2owith resonance)in any solventwith weakly basic,unhinderednucleophile : 2osubstrate(or lo with resonancei)n polarprotic solventwith nucleophilethat is not both hindered anda strongbase

SN2 : 1osubstratein any solventwith nucleophilethatis not both hinderedanda strongbase : 2osubstratein polar aprotic solventwith a weakly basic,unhinderednucleophile

El vs E2

E1 : 3osubstratewith weakly basic,stericallyhinderednucleophiletypically in polar protic solvent : 2osubstratewith weakly basic,stericallyhinderednucleophiletypically in polarprotic solvent

: 3osubstratewith a nucleophilethat is a strongbase(may or may not be hindered- candictatepdt) : 2osubstratewith a nucleophilethat is a strongbase(may or may not be hindered- candictatepdt) : 1osubstratewith a nucleophilethat is a stericallyhinderedstrongbase(must be both)

1 . For the following list of compoundsc, irclethosewhich would be classifiedasa strongbase

(pKaconjugateacid> i5): ('Bu: C(CH3)3)

@@@'RS 'RCon'@'cr-'RS6o4:9

'Hzo'R-NHz

For the following compounds,circlethosewhich would be classifiedashindered: (notes,Me is an

abbreviationfor methyl, CH3, similar to Et, Pr etc.and COz- is shorthandfor anion of carboxylic

acid)

,-\

( lpn)

Y/'

MeoH,(teuoJR, Coz-H, zo,cHro

\--l

,

F-,

cH3

B

r.lt

\'J

eu-g

rH) ,C : c

-

C

H

z-Br

For eachpair of compounds,circlethe strongernucleophile.

((ad)Hc) Hzoo3,c6"*oD(n"*,.D) [33] ,!'3d@

r.lffior N=c

iO[b66Dor (CH3)3coH

\__"/

4. For eachpair of compounds,circlethe betterleavinggroup.

(a)Ho- or@r-r (d)F-,cf. B. olU

(b)cH3sor-96ru

(e)cH,o"-'SP

F$g(oC.lH4rrb)ztrN\tvn6,lceJtJV&fu)veeTqN.JrrhJ, (r) cH3so:o- r(cF1]!)

f\5.,.rt

,

\

(4> b

CHEM 24

Dr. Spence

Providea mechanismfor the following reactions.

,. cr5

\ \l\/

r=lrA-

U

I

5^l I

MeOH

6 .oMe T " )

(J-/})< -w>

Cfll?H

oxrrf

a-''|B',Cr HI

I I 9cH,

\_-/ t-BuO t-BUOH

EL

5xL

bL

cHr

1. NaNH2 2. CH3CH2BT

: /'/\

$

l . NaI. DMSO ) (cH3)3coH

o^-Br "oH -

,=-o -l

\f

-

" t

=

\A

\J

5ot'

FI

/\-\

\J

EL

CHEM24 Providemechanismsfor the first threereactionsin problem 8.

Dr. Spence

') cdl

oJsr s-cfll

?& (7tttz )

Ctl t,

z) &o.,,M, --t

''1, ,' ^ ,/

,

-r>tbotcrt,

r't

'YII :"Pt

c$/ttzotl

bc ( \

c'anadJ 1u 1rcLs*

ertLr /)

crl>

r)"A#,,Lcil)

E+ *J

S/f $*t7

co-F 7)

,J

VT

10. HW assignedfrom the text: 25r26127r28r29r303r 1, 33035,36, 37r 40,4lr 44rsLo57,68

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