1. 1
Organic Chemistry
Course Number: PCH 1120-217
Lecture # 10
Sunday September 29, 2013
Alcohols:
Structure, Nomenclacture, Classification, Phys
ical Properties, Basicity & Acidity and
Preparation of Alcohols
Prof. Oludotun Phillips
Room # 2-81, 2nd Floor Pharmacy Building
Email: dphillips@hsc.edu.kw

2. 2
Alcohols: Learning Objectives
At the end of the class students should be able to:
 discuss the structures and properties of alcohols.
 classification of alcohols.
 discuss the nomenclature (common and IUPAC
names) of alcohols.
 describe the physical properties of alcohols,
basicity and acidity of alcohols.
 discuss the different methods for the preparation of
alcohols.

3. 3
• The functional group of an alcohol is
an -OH group bonded to an sp3
hybridized carbon
– bond angles about the hydroxyl oxygen
atom are approximately 109.5°
• Oxygen is also sp3 hybridized
– two sp3 hybrid orbitals form sigma bonds
to carbon and hydrogen
– the remaining two sp3 hybrid orbitals each
contain an unshared pair of electrons
Alcohols - Structure

4. 4
• IUPAC names
– the parent chain is the longest chain that contains the -
OH group
– number the parent chain in the direction that gives the -
OH group the lower number
– change the suffix -e to -ol
• Common names
– name the alkyl group bonded to oxygen followed by the
word alcohol
Alcohols - Nomenclature

5. 5
• Examples:
Eth an o l
(E th y l alc oh ol)
1-P ro p an ol
(Pro p y l alco h o l)
2-Prop an o l
(Is op ro p y l alco h o l)
1-B u tan o l
(B u ty l alco h o l)
OH
OH
OH
OH
2-B u tan ol
(s ec-B u tyl alco h o l)
2-M e th y l-1-p ro p an o l
(Is ob u ty l alc oh ol)
2-M e th y l-2-p rop an o l
(t ert-B u ty l alco h o l)
OH
Cy clo h e xan o l
(Cy clo h e xy l alco h o l)
OH
OH
OH
Nomenclature of Alcohols

6. 6
• Problem: Write the IUPAC name of each alcohol
O H
CH3 ( CH 2 ) 6 CH2 O H
O H
(a)
(b )
(c)
Nomenclature of Alcohols

7. 7
 Polyhydric alcohols: compounds containing….
– two -OH groups are named as diols,
– three -OH groups are named as triols, etc.
CH3 CH CH2
HO OH
CH2 CH 2
OHOH
CH2 CH CH 2
OHHOH O
1,2-Eth an e d io l
(Eth yle n e gly co l)
1,2-P ro p an e d io l
(P ro p y le n e g lyc ol)
1,2,3-Pro p an e trio l
(G ly ce rol, G ly ce rin )
Nomenclature of Alcohols

8. 8
 Unsaturated alcohols
– the double and triple bond are shown by the infix -en-
and -yn-
– the hydroxyl group is shown by the suffix -ol
– number the chain to give OH the lower number
5
2
OH13
46
tran s- 3-h e xe n e -1-ol
(E)-3-h e xe n e -1-ol
IUPAC Nomenclature of Alcohols
H
OH
5-Hexny-1-ol

9. 9
Alcohols are further classified as:
1. Methyl alcohol (CH3OH)
2. primary (1o)alcohol
2. secondary (2o)alcohol
3. tertiary (3o)alcohol
Classification of Alcohols
H OH
R
H
R' OH
R
H
R' OH
R
R"
(1o) (2o) (3o)
primary secondary tertiary

10. 10
Alcohols are further classified as:
5. allylic alcohol
6. benzylic alcohol
Classification of Alcohols
CH3
CH CHCH2
O H
H
CH3
H
OH CH2
O H C-CH3
OH
H
C-CH3
OH
CH3
Benzylic alcohols
(1o) (2o) (3o)allylic alcohol
(1o primary)

11. 11
 Alcohols are polar compounds
 both the C-O and O-H bonds are polar covalent
-
+
+
O
H
H
H
C
H
Alcohols – Physical Properties

12. 12
 Alcohols associate in the liquid state by hydrogen bonding.
 Hydrogen bonding: the attractive force between a partial
positive charge on hydrogen and a partial negative charge
on a nearby oxygen, nitrogen, or fluorine atom.
– the strength of hydrogen bonding in alcohols is
approximately 2 to 5 kcal/mol.
– hydrogen bonds are considerably weaker than covalent
bonds (for example, 110 kcal/mol for an O-H bond).
– hydrogen bonding can have a significant effect on
physical properties.
Alcohols – Physical Properties

13. 13
– association of ethanol molecules in the liquid state, with
two of the three possible hydrogen bonds to the upper
oxygen are shown as follows:.
Alcohols – Physical Properties

14. 14
– alcohols have higher boiling points and are more soluble
in water than hydrocarbons
CH3 CH2 CH 2 OH
CH3 CH2 CH 2 CH3
CH3 OH
CH3 CH3
CH3 CH2 OH
CH3 CH2 CH 3
CH3 CH2 CH 2 CH2 CH 2 OH
HOCH2 CH 2 CH2 CH2 OH
CH3 CH2 CH 2 CH2 CH 2 CH3
S tru c tu ral Fo rm u la N am e
M o le cu lar
W e ig h t
(g/m o l)
Boilin g
P oin t
(°C )
S o lu b ility
in W ate r
m e th an o l 32 65 in f in ite
e th an e 30 -89 in s olu b le
e th an ol 46 78 in f in ite
p ro p an e 44 -42 in s olu b le
1-p ro p an o l 60 97 in f in ite
b u tan e 58 0 in s olu b le
1-p e n tan o l 88 138 2.3 g /100 g
1,4-b u tan e d io l 90 230 in f in ite
h e xan e 86 69 in s olu b le
Alcohols – Physical Properties

15. 15
Acidity Constants:
 According to Bronsted-Lowry definitions:
 an acid is a hydrogen ion donor.
 a base is a hydrogen ion acceptor.
The strength of the acid is usually compared
measuring their degree of ionization in water.
Relative Acidity of Alcohols

16. 16
Most alcohols are about the same or slightly weaker
acids than water
– pKa = -logKa
– aqueous solutions of alcohols have the same pH as
that of pure water
–  Alcohols are neutral compounds!
CH 3 O H O H
H
[ CH3 O
-
] [ H3 O
+
]
[ CH3 O H]
CH3 O H O
H
H
+
K a =
+ +
= 3.2 x 10
- 16
p K a = 15.5
Acidity of Alcohols

17. 17
In the presence of strong acids, the oxygen atom of
an alcohol can behave as a weak base
– proton transfer from the strong acid forms an oxonium
ion
– thus, alcohols can function as both very weak acids and
weak bases
– Alcohols can lose a proton to a very strong base, e.g.
NaOH + ROH  RO- Na+ + H2
CH3 CH2 - O-H H O
H
H O
H
H
H2 SO4
CH 3 CH 2 -O H
H
CH 3 CH 2 -O H
H HH
O H
Eth y lo xon iu m ion
(p K a
-2.4)
• •
H y d ron iu m ion
(p K a
-1.7)
Eth an o l
+
+
+
++
• •
+
+
+
Basicity of Alcohols

18. 18
– pKa values for several low-molecular-weight alcohols
( CH3 ) 3 CO H
( CH3 ) 2 CHO H
CH3 CH 2 O H
H 2 O
CH3 OH
CH3 CO O H
H Cl
C om p o u n d p K a
-7
15.5
15.7
15.9
17
18
4.8
h y d ro ge n ch l o ri d e
ace ti c aci d
m e th an o l
w ate r
e th an ol
2-p ro p an o l
2-m e th y l -2-p rop an o l
S tru c tu ral
Form u l a
S tro n g e r
aci d
W e ak e r
aci d
*A l s o gi v e n f o r c om p ari s o n are p K a v al u e s f o r w ate r,
ace ti c aci d , an d h y d ro ge n ch l o ri d e .
Acidity of Alcohols

19. 19
 Alcohols can be prepared by the following methods:
i. Fermentation of carbohydrates
ii. Hydration of alkenes
iii. Nucleophilic substitution reaction
iv. Reduction of aldehydes and ketones
Preparation of Alcohols

20. 20
Alcohols can be prepared by:
i. Fermentation of carbohydrates:
 Fermentation is the decomposition of complex organic
compounds into simpler compounds by the action of
biological catalysts known as enzymes.
 Fermentation of glucose give ethanol:…
Preparation of Alcohols
C6H12O6 CH3CH2OH
enzymes
Glucose ethanol
(a sugar) (an alcohol)

21. 21
Alcohols can be prepared by:
ii. Hydration of alkenes:
 Treatment of alkenes with water in the presence of a
strong acid as a catalytic results in the addition of water
to the double bond (hydration reaction):….
+ H2
OCH2
CH2
CH3
CH2
OH
Preparation of Alcohols
Cyclohexane cyclohexanol
H+
Strong acid
(conc. H2SO4)
+ O HH2
O
H+
Strong acid
(conc. H2SO4)Ethylene Ethanol
b.
a.

22. 22
Alcohols can be prepared by:
iii. Nucleophilic Substitution Reactions:
 Reaction of an alkyl halide in hydroxide ion is a
nucleophilic substitution reaction.
 Primary alcohols are prepared by heating primary
alkyl halides in aqueous sodium hydroxide (NaOH), this
reacion proceed by SN2 mechanism:…
 Since 2o and 3o alkyl halides are likely to give elimination
reaction products, this method is not very useful for
preparing alcohols.
Preparation of Alcohols
CH3
CH2
CH2
Br CH3
CH2
CH2
O H + NaBr+ NaO Haq
heat
1-Bromopropane 1-Propanol
(a 1o alkyl halide) (a 1o alcohol)

23. 23
Alcohols can be prepared by:
iv. Reduction of Aldehydes and Ketones:
a. Alcohols are prepared from carbonyl compounds by reduction
reactions in which hydrogen atoms are added to the carbonyl
group by NaBH4 or LiAlH4 followed by H2O or dilute acid
hydrolysis:…..
Preparation of Alcohols
R C H2
C HO R C H2
C H2
O H
NaBH4
Or
LiAlH4An Aldehyde A 1o alcohol
R C OC H3 R C HC H3
OH
A Ketone A 2o alcohol
NaBH4
Or
LiAlH4
Reagents: Sodium borohydride: (NaBH4) Lithium aluminum hydride (LiAlH4)

24. 24
Alcohols can be prepared by:
iv. Reduction of Aldehydes and Ketones:
b. By Catalytic Hydrogenation involves the addition of
Hydrogen to aldehydes or ketones under pressure to
produce 1o and 2o Alcohols respectively:…..
Preparation of Alcohols
R CH2
CHO R CH2
CH2
OH+ H2
Ni
Pressure
An Aldehyde hydrogen A 1o alcohol
R CO CH3
R CHCH3
O H
+ H2
A Ketone hydrogen A 2o alcohol
Reagents: Nickle (Ni); Hydrogen gas (H2)
Ni
Pressure

25. 25
Alcohols can be prepared by:
iv. Reduction of Aldehydes and Ketones:
c. By Grignard addition to an Aldehyde or Ketone followed
by H2O or dilute acid hydrolysis to produce 1o, 2o and 3o
Alcohols respectively.
 Grignard Reagent is prepared by reacting Magnesium
metal with an Alkyl halide in diethyl ether as solvent.
Preparation of Alcohols
R X R Mg X+ Mg
diethyl ether
(as solvent)
Alkyl halide Magnesium Grignard reagent
R = CH3; CH3CH2; or Ph;
X = Cl; Br; I
In this reaction, the “R” of Grignard reagent
acts as Nucleophile

26. 26
Alcohols can be prepared by:
 Formaldehyde is reduced to 1o alcohol:..
 Aldehydes are reduced to 2o alcohols:…
 Ketones are reduced to 3o alcohols:…
Preparation of Alcohols
H C H
O
H C-H
R"
O- + M gX
+ R "M gX H C-H
R"
O H
Formaldehyde Grignard reagent Magnesium salt of alcohol 1o alcohol
R C O C H3
R C-C H3
R "
O - + M g X
+ R "M g X R C-C H3
R "
O H
R' CH O R' C-H
R"
O- +MgX
+ R"M gX R' C-H
R"
OH
H2O
H+
Aldehyde Grignard reagent Magnesium salt of alcohol 2o alcohol
H2O
H+
H2O
H+
Ketone Grignard reagent Magnesium salt of alcohol 3o alcohol