CHM 201
Chapter 10 Exam Problems
1. The allylic bromination of the alkene below with NBS gives four different
products. Draw the two initially formed free radical intermediates together
with any applicable resonance structures and the four products. Which
product do you expect to be the major one and which is formed in lowest yield?
Identify them both.
CH3
CH3
NBS in CCl4
hν
CH3
+
A
CH3
.
CH3
CH3
CH3
CH3
A'
Br
major
CH3
BrCH2
A'
A
CH3
CH3
Br
.
B
+
CH2
B
CH3
CH3
CH3
.
CH2
CH2
B'
.
B'
Br
lowest yield
2. The relative reactivity of primary : secondary : tertiary sites in free radical
chlorination is 1 : 3.5: 5. The free radical chlorination of 2,5-dimethylhexane
gives three monochlorinated products (all C8H17Cl). Gas Chromatographic
analysis of the product mixture shows three peaks with areas of 60 mm2, 70 mm2
and 50 mm2 (compounds A, B, and C respectively). Draw the three products
and predict which isomer corresponds with each peak in the GC. Show your
work.
.
primary
Cl2, hν
3 possible products
from 3 intermediates
secondary
.
.
tertiary
Cl
(reactivity) x (# H's)
primary
1 x 12 = 12
60 mm2
3.5 x 4 = 14
70 mm2
5 x 2 = 10
50 mm2
secondary
Cl
Cl
tertiary
3. Propose a series of chemical steps that would facilitate the following syntheses:
CH3CH2
1) NBS, hν
a)
2) Li(CH3CH2)2Cu
1) Br2, hν
b)
OCH(CH3)2
2) (CH3)2CHOH
D
c)
OH
1) H2SO4(aq)
2) NBS hν
3) Mg, ether
4) D2O