CHAPTER11 - Practice Exercises (ORGANIC CHEM I)
________DR. PAHLAVAN
1. Arrange the following to the leaving group ability (basicity)
F- , Cl- , I- , Br2. Identify the type of the following solvent as polar protic or polar aprotic.
CH3OH
(CH3)3 S =O
CH3 C ≡ N
(CH3)2NCHO
H2O
3. From each pair, select the stronger nucleophile;
a)
H2O , OH-
d)
CH3OCH3 , CH3SCH3
b) CH3COO - , OH -
c ) CH3SH , CH3S -
e) Cl - , I – ( in DMSO)
f) Cl – or I - ( in methanol)
4. Consider the following statement in reference to SN1 , SN2 , E1 , and E2 reactions of alkyl halides. To which
mechanism(s), if any, does each statement apply?
_____ a. Involves a carbocation intermediate.
_____ b. Is first-order in alkyl halide and first - order in nucleophile
_____ c. Involves inversion of configuration at the site of substitution.
_____ d. Involves retention of configuration at the site of substitution.
_____ e. Substituent at a stereocenter gives predominately a racemic product.
_____ f. Is first-order in alkyl halide and second –order in base.
_____ g. Is first- order in alkyl halide and first- order in base.
_____ h. Is greatly accelerated in protic solvents of increasing polarity.
_____ i. Rearrangement are common.
_____ j. Order of reactivity is 3o > 2o > 1o > methyl.
_____ k. Order of reactivity is methyl > 1o > 2o > 3o
5. Arrange these alkyl halides in order of increasing E2 to SN2 products observed on reaction of each with
sodium ethoxide, CH3O– Na+ , in ethanol. ( highest = 4, lowest = 1)
CH3
CH3CH2Br
CH3CH2CH2Br
CH3 - C - CH2CH3
Cl
1
CH3
CH3 - CH - CH2CH2 Br
6. Draw Free- Energy profiles for SN1 and SN2 reactions. Label you graph completely.
7. Complete the following reactions;
Cl
CH3CH2OH
+ CH3CH2 O Na
a)
substitution
elimination
CH3
b)
CH3C
Br
C: Na
substitution
Br
c)
Br
+ CH3 O Na
C6H5 - CH - CH - C6H5
elimination
E2
CH3OH
( E and Z products)
CH3
C - CH3
d)
+
CH3
CH3CH2 O Na
E2
ethanol
Cl
CH3
e)
CH3 O Na
CH3 - C - Cl
+
E2
CH3
CH3
f)
CH3 - Cl
+
CH3 - C - O Na
SN2
CH3
Br
methanol
g)
+
CH3OH
E1 and SN1
2
8. Predict whether each reaction proceeds predominately by substitution, elimination, or whether the two
combined. Write structure formula for the major organic product(s).
CH3
80 deg.
CH3 - C - CH2CH3
a)
+ NaOH
H2O
Cl
CH3
80 deg.
b)
CH3 - CH - CH2CH2Br
c)
+ (C2H5)3 N:
CH3 O Na
+
toluene
methanol
I
Cl
acetone
I
+ Na
d)
CH3
CH2CH2Br
Na CN
+
e)
methanol
9. Complete the following nucleophilic substitution;
a) : I
b)
+ CH3 - CH2 - CH2 - Cl
H3N:
+
Br
c)
CH3 - CH2 O:
d)
CH3CH2 S
+
+
CH2 = CH - CH2 -Cl
CH3 - CH - CH2CH3
I
e)
CH3 - C
C:
+ CH3 - CH - CH2 - CH2Br
CH3
3
10. Rank the followings in order of increasing the reactivity ( highest =4 , lowest =1).
a) Substrate Effects –( reactivity in SN1 reaction)
H
H
CH3
CH3
CH3
Br
Br
H
Br
CH3
CH3
H
H
Br
CH3
H
b) Carbocation stability (reactivity in SN1 and E1)
H
H
CH3
CH3
C
C
H
CH3
H
CH3
H
CH3
C
C
CH3
H
Nuceolphie Effects (reactivity in SN1 and E1)
H
H
CH3
CH3
C
C
H
CH3
H
CH3
H
CH3
C
C
CH3
H
c) Leaving Group Effects ( reactivity in SN1 and E1 reactions)
H2N
Br
Cl
RO
TosO
I
HO
H2N
d) Solvents Effects ( solvent promotion of SN1 and E1 reactions
Hydrocarbons
(C6H14)
Alcohols
(CH3CH2OH)
Water/alcohol
(H2O / CH3CH2OH)
4
Water
H2O