Alcohols, Phenols and
Ethers
Fundamentals of General, organic and Biological chemistry; McMurry et al., 5ed, Prentice Hall
Alcohol and Phenols have –OH group (hydroxyl functionality). Polar.
The presence of the hydroxyl group makes them miscible with water
The –OH group participates in H-bonding
Alcohols up to C5 are very soluble in water. After that solubility
decreases with increasing number of Carbon atoms
Alcohols
Naming alcohols
•Start with the parent chain and replace the hydrocarbon –e ending with –ol
•Number the hydrocarbon chain. The carbon containing the –OH group should
have the lowest number
•Number the position of the –OH group
•Number and name other side chains or functionalities using IUPAC rules
1-butanol
2-methyl-1-propanol
Primary /secondary/tertiary
2-butanol
A 2o alcohol (secondary)
2-methyl-2-propanol
A 3o alcohol (tertiary)
1-propanol (1o alcohol)
Distinguish the difference between 1o, 2o and 3o structures
Nomenclature contd.
In a cyclic alcohol, it is understood that the –OH group is on C-1
Alcohols
What is the identitity of this molecule?
2-isopropyl-5-methylcyclohexanol
Menthol
Alcohols (diols, triols)
•-diols or –triols mean two or three hydroxy groups in the molecule
•Number the hydroxy group carbons with the lowest possible numbers
•Prefix uses the full parent name, i.e butane
,
Ethane-1,2-diol (ethylene glycol)
Propane-1,2,3-triol (glycerol)
Properties of alcohols
• Alcohols are polar compounds because the –OH
group participates in H-bonding
• Smaller straight chain alcohols are usually liquids
• Alcohols such as 1-heptanol (C8) tends to act more
like alkanes
• Diols and triols have higher b.p’s and are more water
soluble
Reactions of alcohols
• Dehydration: Loss of water to form an
alkene. Occurs in presence of acid catalyst
• Oxidation: In presence of oxidizing agents
alcohols get oxidized to carbonyl compounds
Dehydration reaction
Fundamentals of General, organic and Biological chemistry; McMurry et al., 5ed, Prentice Hall
Dehydration of alcohols
Hint- More substituted alkene will be major product
Dehydration of alcohols
Predict the starting alcohol in the following:
?
?
Write all possible structures then keep the most substituted ones!
Oxidation
*Note- Depending upon the alcohol and reaction conditions a different types
and mixtures of carbonyl products may be formed
Image Adapted from http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch15/ch15-4-6.html
Oxidation of alcohols
Secondary alcohols get converted to ketones upon oxidation but no further
Q: What is oxidation reaction for a tertiary alcohol
Image Adapted from http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch15/ch15-4-6.html
Oxidation of alcohols
?
?
Hydroxybenzene (a.k.a Phenol)
• Have been used as an antiseptic
•Many OTC sore throat medications contain substituted phenols
•Most phenols are somewhat water soluble
•BHA and BHT are often used as food preservatives
BHA
BHT
Acidity of phenols
Alcohols and Phenols are weakly acidic
They dissociate in water to give the alkoxide or the phenoxide anion
Phenols
• Methanol and Ethanols are as acidic as water, i.e weak acids,
Ka = 10-15
• Their anion (alkoxide ion) is a strong base, similar to the hydroxide
ion
• Phenols are more acidic than alcohols
• Phenolic Ka is 1.0X 10-10