Alkyl Halides

1
Chapter 10

• Alkyl Halides

2
Alkyl Halides

• Naming
• Synthesis - from alkene, alkane, alcohol
• Reactions - Organometallic

3
Naming
1,3-Dichloro-3-methylbutane
4
Naming


2-Bromo-5-chlorohexane
(R or S)-2-Bromo-(R or S )-5-chlorohexane (if
3-dimension structure is given)
5
Naming



4-sec-Butyl-2-chlorononane
6
Naming
1,1-Dibromo-4-tert-butylcyclohexane
7
Naming

5-Iodo-2-hexene
8
Naming
1-Bromo-6-chloro-2-hexyne
9
Naming


cis-1-Bromo-2-ethylcyclopentane
cis-(R)-1-Bromo-(S)-2-ethylcyclopentane
10
Alkyl Halides

• Naming
• Synthesis - from alkene, alkane, alcohol
• Reactions - Organometallic

11
Synthesis

• Alkene HX(XCl, Br, or I) or X2 (XCl or Br )
• Radical Halogenation of Alkanes
• Allylic Halogenation of Alkenes
• From Alcohol

12
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
13
Synthesis

• Alkene HX(XCl, Br, or I) or X2 (XCl or Br )
• Radical Halogenation of Alkanes
• Allylic Halogenation of Alkenes
• From Alcohol

14
Radical Chlorination of Methane
h? or heat
h? or heat
h? or heat
15
Chlorination of alkanes
Monochloro-
Chiral, racemic

achiral
achiral

others...
chiral, racemic

chiral, racemic
achiral
16
Chlorination of alkanes
Monochloro-
1o
3o
and others...
2o
2o
Yields are different, with 3o gt 2o gt 1o (see p.
361)
1o
17
relative reactivity(rr)
expected yield
H ? rr
H
6
1.0
6.0
21
1
5.0
5.0
18
2
3.5
7.0
25
2
3.5
7.0
25
3
1.0
3.0
11
? 28.0
see p. 361
18
Radical Chlorination of Alkane
Yields 3o gt 2o gt 1o implies that ...
Hammond Postulate
19
Synthesis

• Alkene HX(XCl, Br, or I) or X2 (XCl or Br )
• Radical Halogenation of Alkanes
• Allylic Halogenation of Alkenes
• From Alcohol

20
Allylic
p 172, Table 5.3
1. Radical reactions take place at the allylic
position. 2. Allylic hydrogen is more acidic than
alkyl and vinylic hydrogen.
21
Radical Chlorination of Alkane
Stability
22
Allylic vs. vinylic Stability
Resonance

more stable
No resonance
less stable
23

p 364
3-Bromocyclohexene


24
Synthesis

• Alkene HX(XCl, Br, or I) or X2 (XCl or Br )
• Radical Halogenation of Alkanes
• Allylic Halogenation of Alkenes
• From Alcohol

25
Alcohol ? Alkyl Halides
ROH HX ? RX H2O
26
ROH HX ? RX H2O
Ethers, carbonyl, and aromatic rings do not
interfere.
High yield
27
Synthesis

• Alkene HX(XCl, Br, or I) or X2 (XCl or Br )
• Radical Halogenation of Alkanes
• Allylic Halogenation of Alkenes
• From Alcohol

28
Alkyl Halides

• Naming
• Synthesis - from alkene, alkane, alcohol
• Reactions - Organometallic

29
Organometallic Reactions
Organomagnesium halides, RMgX, - Grignard
Reagents.
R 1o, 2o, 3o, alkyl, alkenyl (vinyl), or aryl.
X Cl, Br, or I
30
Organometallic Reactions
Organolithium reagent, RLi.
31
Organometallic Compound
1. Although RMgX and Rli are polar covalent, they
are still soluble in nonpolar pentane.
2. RMgX and RLi are strong bases.
32
51
38-40
pKa
pKa
1. RMgX is a strong base.
2. CH3CH2MgBr will react with all the
listed compounds.
33
Organometallic Reactions
Lengthen small molecules.
34
Alkyl Halides

• Naming
• Synthesis - from alkene, alkane, alcohol
• Reactions - Organometallic