1. Alcohols
د. جهاد الماليطي

2. Structure - Alcohols Alcohols R-O-H
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 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
Draw the orbitals of CH3OH

3. Classification
A primary (1°) alcohol is one in which the carbon atom with the OH group is attached to one other carbon atom (in blue). Its general formula is RCH2OH.
A secondary (2°) alcohol is one in which the carbon atom with the OH group is attached to two other carbon atoms (in blue). Its general formula is R2CHOH.
A tertiary (3°) alcohol is one in which the carbon atom with the OH group is attached to three other carbon atoms (in blue). Its general formula is R3COH.
Aromatic (phenol): -OH is bonded to a benzene ring.

4. Nomenclature-Alcohols
IUPAC names
the parent chain is the longest chain that contains the OH group
number the parent chain to give the OH group the lowest possible number
change the suffix -e to -ol
IUPAC names for simple Unbranched Alkyl
Name
Molecular Formula
Structural Formula
methane
CH4
hexane
C6H14
CH3(CH2)4CH3
ethane
C2H6
CH3CH3
heptane
C7H16
CH3(CH2)5CH3
propane
C3H8
CH3CH2CH3
octane
C8H18
CH3(CH2)6CH3
butane
C4H10
CH3CH2CH2CH3
nonane
C9H20
CH3(CH2)7CH3
pentane
C5H12
CH3(CH2)3CH3
decane
C10H22
CH3(CH2)8CH3

5. Nomenclature-Alcohols
Common names
name the alkyl group bonded to oxygen followed by the word alcohol

6. Nomenclature-Alcohols
Examples

7. Nomenclature of Alcohols
Compounds containing more than one OH group are named diols, triols, etc.
For common Names: 1, 2 diols (vicinal diols) are called glycols. C H 3 2 C H 2 C H 2 O H O H H O O H H O H O O H
1,2-Ethanediol
(Ethylene glycol)
1,2-Propanediol
(Propylene glycol)
1,2,3-Propanetriol
(Glycerol, Glycerine)

8. Nomenclature of Alcohols
Unsaturated alcohols
show the double bond by changing the infix from -an- to -en-
show the the OH group by the suffix -ol
number the chain to give OH the lower number

9. Nomenclature of Alcohols - Naming Priority
7- Alkenes
8- Alkynes
9- Alkanes
10- Ethers
11- Halides
1- Acids
2- Esters
3- Aldehydes
4- Ketones
5- Alcohols
6- Amines
Don’t worry about this

10. Nomenclature of Alcohols
When -OH is part of a higher priority class of compound, it is named as hydroxy.
Example:
4-hydroxybutanoic acid

11. Naming Phenols -OH group is assumed to be on carbon 1.
For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4.
Methyl phenols are cresols.
4-methylphenol
para-cresol
3-chlorophenol
meta-chlorophenol

12. Physical Properties Alcohols are polar compounds
they interact with themselves and with other polar compounds by dipole-dipole interactions
Dipole-dipole interaction: the attraction between the positive end of one dipole and the negative end of another

13. Physical Properties
Hydrogen bonding: when the positive end of one dipole is an H bonded to F, O, or N (atoms of high electronegativity) and the other end is F, O, or N
the strength of hydrogen bonding in water is approximately 21 kJ (5 kcal)/mol
hydrogen bonds are considerably weaker than covalent bonds
nonetheless, they can have a significant effect on physical properties

14. Physical Properties
Ethanol and dimethyl ether are constitutional isomers.
Their boiling points are dramatically different
ethanol forms intermolecular hydrogen bonds which increase attractive forces between its molecules resulting in a higher boiling point
there is no comparable attractive force between molecules of dimethyl ether C H 3 2 O C H 3 O
Ethanol
Dimethyl ether
bp 78° C
bp -24°C

15. Physical Properties
In relation to alkanes of comparable size and molecular weight, alcohols
have higher boiling points
are more soluble in water
The presence of additional -OH groups in a molecule further increases solubility in water and boiling point

16. Physical Properties

17. Acidity of Alcohols
In dilute aqueous solution, alcohols are weakly acidic
Ka acid dissociation constant

18. Acidity of Alcohols

19. Acidity of Alcohols pKa range: 15.5-18.0 (water: 15.7)
Acidity decreases as alkyl group increases.
Halogens increase the acidity.
Phenol is 100 million times more acidic than cyclohexanol!

20. Table of Ka Values
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21. Formation of Alkoxide Ions
React methanol and ethanol with sodium metal (redox reaction).

22. Formation of Phenoxide Ion
Phenol reacts with hydroxide ions to form phenoxide ions - no redox is necessary. O H O + O H + H O H p K = 1 5 . 7 a p K = 1 a