Chapter 17: Alcohols and Phenols
Naming of Alkyl Alcohols:
H H R
H OH R OH R OH
R R R
Primary Secondary Tertiary
Alcohol Alcohol Alcohol
Compounds that have the alcohol functional group as the highest priority group end with the suffix -ol.
IUPAC Rules for Naming Alcohols:
1. Find the root name by selecting the alkyl chain that posses the hydroxyl functional group and adding
the -ol suffix on the end instead of the -e.
2. Number the alkane chain beginning at the end nearer the hydroxyl group.
3. Number the substituents according to chain position and list names in alphabetical order.
1-Bromo-3-pentanol 3-Ethyl-7,7-dimethyl-2-octanol trans-4-Methyl-cyclohexanol 2-Methyl-2-propanol
Naming of Phenols (Aromatic Alcohols):
Phenols only refer to compounds with hydroxyl groups driectly on the phenyl ring. These compounds are
named in the same manner as substituted benzenes with the exception that the word benzene in the name is
switched with the word phenol.
Special Properties of Alcohols:
Boiling points of alkyl alcohols are elevated
relative to the correspodning alkane or alkanes
δ Oδ δ Oδ
with similar molecular weights. This property δ
is a result of the hydrogen bonding observed in H H
O δ O
hydroxylated compounds. Phenols also δ δ
experience the same property relative to non-
hyroxy aromatic compounds.
Representative Hydrogen Bonding in Ethanol
Alcohols can be both weakly acidic and weakly basic.
R O H R O R O
(Strong Acid) Alkoxide Anion
H H H
Alcohol acting Oxonium Ion Alcohol acting
as a Base as an Acid
Electron witdrawing groups on the alcohol increase acidity and electron donating groups decrease acidity.
In general phenols are more acidic then alkyl alcohols. Alcohols are acidic enough to react with baes such as
NaH, NaNH2, Grinard reagents (MgXR), and Lithium Reagents. Alkoxides are generally strong bases.
Preparations of Alcohols
Acid catalyzed addition of water to an alkene:
HO H OH
H H2O -H
note: intermediate carbocation can lead to undesireable reactions
Oxymercuration of alkenes:
Hg Hg OAc H2O
Hydroboration (no mechanism), always produces anti Markovnikov product, with syn regioselectivity:
OH Added H and OH are syn
(1) BH3, THF
(2) H2O2, - OH
peracid O OH
hydroxyl groups add anti to one another
hydroxyl groups add syn to one another
KMNO4 gives same reaction OH
Reduction of Carbonyl Compounds to Generate Alcohols
O OH O OH
R H agent R H agent
R R' R R'
aldehyde primary ketone secondary
Common Reducing Agents Both of these reagents function by providing a hydride nucleophile H
NaBH4 - Sodium Borohydride - can reduce both aldehydes and ketones, reduces esters very slowly won't
reduce carboxylic acids at all, overall more mild.
LiAlH4 - Lithium Aluminum Hydride- can reduce aldehydes, ketones, esters, and acids, more dangerous.
O NaBH4 OH LiAlH4
LiAlH4 O LiAlH4
OH + 2 Methanol
Reaction of Grignard Reagents with Aldehydes and Ketones
δ δ O OH
Mg R1 R2 H3O
R X R MgX
diethyl ether R1 R2 R1 R2
X=Cl, Br, or I
R=primary, secondary, tertiary, aryl, or vinylic
Reaction of Grignard Reagents with Aldehydes and Ketones
O δ δ O O OH
R MgX R MgX H3O
R2 R1 R R1 R
R1 O R1 R
Grignard Reagents will react with acidic protons to form an alkane. -OH, -NH, -SH, -COOH are acidic enough
to destroy the Grignard. Grignards also can not be made from alkyl halides that also contain carbonyls, since
the formed Grignard will react with iteslf. Fortunately, this problem can be overcome by protecting these
sensitive groups when using Grignards
Reactions of Alcohols
Dehydration-the loss of H2O from an alcohol to yield the alkene, acid catalyzed, follows the Zaitsev Rule, that
is this reaction gives the more stable substituted product, only preparatively useful with tertiary alcohols.
OH H2SO4 - H2O
Dehydration with phosphorus oxychloride (POCl3):
OH POCl3 essentially converts -OH into a good leaving group and
then procedes through an E2 mechansim.
Pinacol Rearrangement: acid catalyzed reaction with vicinal diols
R2 R3 R2
R2 R3 R2 R3 R1
R1 R4 R1 R4 R1 R3
OH OH OH OH2
OH R4 HO R4
R1 R2 R2
HO R4 H O R4 O R4
Groups migrate according to Migratory Aptitude: phenyl, alkyl, hydrogen
Coversion of an alcohol to an alkyl halide:
tertiary alcohols: use HX, dehydration SN1 mechanism with halogen nuclophile
primary and secondary: use SOCl2 or PBr3 , both occur by an SN2 mechansim with inversion of stereochem
Tosylation of Alcohols: OH O
TosCl O S
Tosyl chloride in pyridine makes the tosyl ester
Tosylation doesn't invert stereochemsitry pyridine O
Oxidation of Alcohols: An alcohol can be oxidized to yeild a carbonyl compound.
Primary alcohols can be oxidized to an aldehyde or further to a carboxylic acid. Secondary alcohols can be
oxidized to ketones, tertiary alcohols cannot be oxidized.
Oxidation O O O
HO Oxidation Oxidation
Common Oxidizing Agents:
CrO3 typical oxidants- will oxidize primary alcohols to carboxylic acids and secondary alcohols to ketones
PCC (Pyridine CrO3Cl)-generally used for oxidizing primary alcohols to aldehydes.
Alcohol Protection: Protection is often needed in syntesis, for example when carrying out the Grignard
Reaction. The protecting group is attached to the substrate the reaction is carried out and then the protecting
group is removed.
Trimethylsilyl chloride protection of alcohols
Dihydropyaran protection of alcohols
R OH Si
O R R OH
H O O
Pyridine R O
deprotection: AcOH, THF, H2O
deprotection: H , H2O, F
Tert-butanol protection of alcohols
R OH R
deprotection: H , H2O
Preparation of Phenols
Oxidation of cumene to phenol
O2 H3O O
Alkali fusion to produce phenol
Note: the alkali fusion reaction requires harsh
solvent free conditions, therefore it is typically
NaOH, high heat
only useful with alkyl goups present on the ring
Reactions of Phenols - Phenols are higly activated towards electrophilic aromatic stubstitution.
OH O Na O
NaBH4 or SnCl2/ H2O