Chapter 4 -

1
Chapter 4 - Alcohols and Alkyl Halides

• Functional groups and nomenclature
• Role of intermolecular forces on properties
• Synthesis of alkyl halides from alcohols
• Two reaction mechanisms SN1 and SN2cation
  stability and the Hammond Postulate
• Additional ways to prepare RX from ROH
• Halogenation of alkanes reactivity-selectivity
  principle, radical stability and chain reactions
• All sections are covered.

2
Functional Groups and Priorities
Nomenclature assembles names like trees start
with a parent structure (e.g., an alkane), then
add prefixes and a functional group (FG) suffix.
FGs are the centers of reactivity within
molecules and have predictable chemical
behavior. In naming, FGs are usually higher
priority than a substituent. In more complicated
names, FGs can be indicated by a prefix. IUPAC
naming of acyclic compounds Double and triple
bonds are incorporated into the parent chain, as
much as possible, resulting in a modified
hydrocarbon name. Beyond their presence in the
parent chain, they are numbered in a prioritized
fashion with any other FGs that are present.
3
FG Priority List HighCarboxylateCarboxylic
acid Anhydride Ester Acid halide Amide Nitrile Ald
ehyde Ketone Alcohol (phenol) Amine Ether AlkeneA
lkyne Alkyl halide, phenyl, alkyl Low
4
IUPAC Nomenclature of Alkyl Halides

• In the formal IUPAC system, alkyl halides are
  named as substituted alkanes F, fluoro Cl,
  chloro Br, bromo I, iodo. In common naming,
  they are named as halides (e.g., methyl
  chloride).
• 2. Halogens are treated as substituents of equal
  priority to alkyl groups.

4-chloro-3,3-dimethyl-6-(1-methylethyl)nonane or 4
-chloro-6-isopropyl-3,3-dimethylnonane
4-bromo-2-iodo-1-methylcyclohexane
5
Classification of Alkyl Halides
1
2
3
tert-butyl bromide (common) Or 2-bromo-2-methylpr
opane (IUPAC)
n-butyl bromide (common) or 1-bromobutane (IUPAC)
sec-butyl bromide (common) or 2-bromobutane
(IUPAC)
6
Nomenclature of Alcohols
In an alcohol, the OH is a high-priority
functional group.
IUPAC NAME substituent prefixesparentfunction
al group suffix(es). For alcohols, alkane suffix
e changes to ol.
1. Determine the parent hydrocarbon containing
the functional group. On cyclic compounds,
OH receives number 1 only show the 1 if
multiple OH groups are present. 2. If necessary,
the suffix is preceded by a positional identifier.


both o.k. as formal names
7
Alcohols can be categorized as primary (1),
secondary (2),and tertiary (3) by the number
of carbons directly attached to the
hydroxyl-bearing carbon.
1
3
2
8
Classification of amines is different than ROH or
RX.
1-butanamine or butan-1-amine A primary (1)
amine, one C attached to N
N-ethyl-3-heptanamine A secondary (2) amine,
two C attached to N
2-ethyl-N-methyl-N-propylcyclohexanamine A
tertiary (3) amine, three C attached to N
9
Hybridization and Bonding in ROH
10
Recall
A hydrogen bond is a very strong dipoledipole
interaction ONLY occurs when N-H, O-H, and F-H
bonds (H-bond donors)interact with N, O, and F
atoms (H-bond acceptors).
Solubility of hydrogen-bondable molecules in
water depends upontheir proportion of H-bond
donor/acceptor atoms.
11
Effect of Structure on Boiling Point
CH3CH2CH3
CH3CH2OH
CH3CH2F
Molecularweight Boilingpoint,
C Dipolemoment, D

• 44 48 46
• -42 -32 78
• 0 1.9 1.7

12
Polarizability

• Distortion of electron clouds is important to van
  der Waals attractive interactions (induced
  dipole-induced dipole).
• Increasing the atomic radii within a group raises
  the boiling point.

13
Example Boiling point increases with increasing
number of halogens
Compound Boiling Point
CH3Cl -24C CH2Cl2 40C CHCl3 61C CCl4
77C
Zero dipole moment
Even though CCl4 is the only compound in this
list without a dipole moment, it has the highest
boiling point. Induced dipole-induced dipole
forces are greatest in CCl4 because it has the
greatest number of Cl atoms. Cl is more
polarizable than H.
14
???
15
Reaction Mechanisms
We will dissect the reactions of alcohols with HX
to make alkylhalides to learn about reaction
mechanisms. There are two main reaction types
SN1 and SN2. We will define these names in a few
minutes. Example (CH3)3COH HCl ------gt
(CH3)3CCl HOH This reaction is a
substitution reaction, but the net reaction
doesnot give the details of the reaction
mechanism, or path.
Ten new terms Elementary step Intermediate
Transition state Oxonium ion Activation
barrier Carbocation Concerted
reaction Nucleophile Molecularity Electrophi
le
16
Reaction Pathway
Energy Barrier
2nd intermediate
Products
Intermediate
17
tert-butanol HCl, 1st elementary step
pKa -3.9
pKa -2
Intermediates
18
tert-butanol HCl, 2nd elementary step

• Hammond Postulate If the structure of a
  transition state is similar in energy to the
  species immediately preceding or following it,
  the transition state structure will most resemble
  that species.

19
tert-butanol HCl, 3rd elementary step
Alkyl Chloride
20
Potential Energy Diagram of SN1 Reaction of an
Alcohol with HX
Rate kalkyloxonium ion
Mechanisms can be supported or disproved, but
cannot be proven correct.