1. Unit 6 – Alcohols and Ethers
Types of Alcohols
Nomenclature
Properties of Alcohols
Synthesis of Alcohols
Reactions of Alcohols

2. Types of Alcohols Alcohol:
organic compound containing one or more hydroxyl (OH) groups.
Alcohols are often classified by the type of carbinol carbon atom present
the carbon bonded to the OH group
Methanol
wood alcohol
Ethanol
drinking alcohol
Isopropyl alcohol
rubbing alcohol

3. Types of Alcohols Primary alcohol: the carbinol carbon is attached
to one other carbon atom
Secondary alcohol:
the carbinol carbon is attached
to two other carbon atoms
Tertiary alcohol:
to three other carbon atoms

4. Types of Alcohols Ethylene glycol car antifreeze propylene glycol
Diol:
an alcohol with two OH groups
Glycol:
a vicinal diol
OH groups on adjacent carbons
Ethylene glycol
car antifreeze
propylene glycol
medicine, food

5. Types of Alcohols phenol 3-methyl-1-butanethiol Phenol:
a compound with a hydroxyl group bonded directly to an aromatic (benzene) ring
Thiols:
an organic compound with an SH group
sulfur analog of alcohols
also called mercaptans
phenol
3-methyl-1-butanethiol

6. IR of Alcohols
Alcohols typically exhibit a strong, broad, rounded peak at about 3300 cm-1+ for the O-H bond.
SDBSWeb : (National Institute of Advanced Industrial Science and Technology, 11/1/09)

7. IR of Alcohols
In the absence of hydrogen bonding, the O – H peak can be relatively sharp and hard to distinguish from an N – H peak.
The frequency for an O-H peak in the absence of hydrogen bonding is typically somewhat higher (~3600 cm-1).
The O-H peak for a carboxylic acid is much broader and typically spans the distance from ~2500 – 3500 cm-1.

8. IR of Alcohols acid O-H acid O-H alcohol O-H w/hydrogen bonding
alcohol O-H w/o hydrogen bonding

9. Nomenclature a substituted pentanol IUPAC Naming System for Alcohols:
Find the longest continuous chain that contains the carbinol carbon atom
Drop the “e” from the corresponding alkane name and add the suffix “ol”
a substituted pentanol

10. Nomenclature (2R, 3R)-3-methyl-2-pentanol
IUPAC Naming System for Alcohols:
Number the longest chain starting from the end closest to the OH group.
OH takes priority over double and triple bonds
OH group is assumed to be on C #1 on a cycloalkane ring
Name and number all substituents as with an alkane or alkene.
Don’t forget R or S if appropriate.
(2R, 3R)-3-methyl-2-pentanol

11. Nomenclature 4-methyl-5-hexen-1-ol 4-methylhex-5-en-1-ol
To name an alcohol that contains a double bond:
use “ol” suffix after the name of the alkene (drop the last “e”)
number the chain to give the carbinol carbon the lowest possible number
place the position number for the C=C in front of the base name (or before the “en”) and the position number for the OH in front of the “ol” suffix
4-methyl-5-hexen-1-ol
4-methylhex-5-en-1-ol

12. Nomenclature 2, 3-pentanediol or pentane-2, 3-diol To name diols:
use suffix “diol” after the name of the alkane (keep the ending “e”)
indicate the position of each OH group
place position of each OH group in front of the base name or in front of the suffix “diol”
2, 3-pentanediol or
pentane-2, 3-diol

13. Nomenclature 2-pentanethiol 3-methyl-2-pentanethiol To name thiols:
Use the same rules for naming alcohols
use “thiol” suffix instead of “ol” suffix
2-pentanethiol
3-methyl-2-pentanethiol

14. Nomenclature Common names are often used with phenols: 2-bromophenolor
ortho-bromophenol
phenol
3-nitrophenol or
meta-nitrophenol
4-chlorophenol or
para-chlorophenol
ortho = 1, meta = 1, para = 1,4

15. Nomenclature Common names are often used with phenols: 2-methylphenol
ortho-cresol
4-methylphenol
para-cresol
Benzene-1,2-diol
catechol
Benzene-1,3-diol
resorcinol
Benzene-1,4-diol
hydroquinone

16. Nomenclature
Example: Name the following compounds:

17. Nomenclature Example: Draw the structures of the following compounds.
3-isopropyl-2-methyl-2-hexanol
trans-2-bromocyclohexanol
(E)-2-chloro-2-buten-1-ol

18. Properties of Alcohols
The physical properties of alcohols are strongly influenced by the presence of the hydrophilic (“water loving”) OH group.
The OH group is capable of forming hydrogen bonds with other alcohol groups or with water.

19. Properties of Alcohols
Due to hydrogen bonding, alcohols have significantly higher boiling points than alkanes with comparable molecular weights.
CH3CH2OH MW = 46
BP = 78oC
CH3CH2CH3 MW = 44
BP = - 42oC

20. Properties of Alcohols
BP increases as the amount of hydrogen bonding increases:
1-propanol BP = 97oC
1,2-propanediol BP = 188oC
(propylene glycol)
1,2,3-propanetriol BP = 290oC
(Glycerol)

21. Physical Properties
Alcohols with 1-3 carbons are soluble in water.

22. Properties of Alcohols
Solubility decreases as the size of the alkyl group increases.
1-hexanol is less soluble than ethanol
Solubility increases as the alkyl group becomes more compact/spherical.
t-butyl alcohol is more soluble than 1-butanol.
Solubility increases with increasing number of OH groups.

23. Acidity of Alcohols and Phenols
The acidity of alcohols varies widely and can be expressed using the acid dissociation constant, Ka
ROH + H2O RO- + H3O+
Ka = [RO-][H3O+] pKa = -log Ka
[ROH]
Acidity increases as:
Ka increases
pKa decreases
Alkoxide ion

24. Acidity of Alcohols and Phenols
Structural trends and acidity:
Acidity of H2O, CH3OH, and CH3CH2OH are similar. (pKa = 15.7, 15.5, and 15.9 respectively)
Acidity decreases as number of carbons in the R group increases.
CH3OH pKa = 15.5
t-butyl alcohol pKa = 18.0

25. Acidity of Alcohols and Phenols
Structural trends and acidity:
Acidity increases with the addition of electron-withdrawing halogens
pKa = 14.3
pKa = 12.2
pKa = 15.9

26. Acidity of Alcohols and Phenols
Structural trends and acidity:
Phenols are more acidic than water or alcohols
pKa = 18.0
pKa = 10.0

27. Acidity of Alcohols and Phenols
Phenols are stronger acids than alcohols.
React readily with aqueous NaOH
Phenols are soluble in aqueous strong base solutions but are insoluble in aqueous NaHCO3. +
Sodium phenoxide

28. Acidity of Alcohols and Phenols
Since alcohols are very weak acids, a very strong base is used to remove the acidic proton.
Unless they are water soluble, alcohols are not soluble in aqueous base solution.

29. Synthesis of Alcohols Nucleophilic Substitution on an alkyl halide
SN2 conditions most useful
strong nucleophile
methyl > 1o > 2o
inversion of configuration

30. Synthesis of Alcohols Acid Catalyzed Hydration (Hydrolysis) of Alkenes
Markovnikov product formed
Equilibrium process
Less useful synthetically than other methods
rearrangements often occur

31. Synthesis of Alcohols Oxymercuration-Demercuration of Alkenes
Markovnikov product
Anti addition to double bond

32. Synthesis of Alcohols Hydroboration-Oxidation of Alkenes
Anti-Markovnikov product
Syn addition to double bond

33. Synthesis of Alcohols or Syn Hydroxylation of Alkenes
Syn addition to double bond
Reagents:
OsO4, H2O2
cold, dilute KMnO4, OH- or

34. Synthesis of Alcohols Anti-Hydroxylation of Alkenes
epoxide intermediate
Anti addition to double bond
Common peroxyacids:
CH3CO3H
MCPBA