Alcohols • Contain a hydroxyl (-OH) group R O H + − • Intermolecular forces: dipole-dipole, H- bonding • H-bonds between alcohol molecules: high boiling points • H-bonds with water: up to 4-carbon alcohols soluble in water • -OH group can act as a weak base or a weak acid R OH R O H H R O + Strong acid + Strong base H 3 C O H H 3 C O H H O H alkoxide oxonium ion alcohol
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Alcohols Contain a hydroxyl (-OH) group ++ −− Intermolecular forces: dipole-dipole, H-bonding H-bonds between alcohol molecules: high boiling points.
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Alcohols• Contain a hydroxyl (-OH) group
RO
H +
−
• Intermolecular forces: dipole-dipole, H-bonding• H-bonds between alcohol molecules: high boiling points
• H-bonds with water: up to 4-carbon alcohols soluble in water
• -OH group can act as a weak base or a weak acid
R OH R O
H
H
R O + Strong acid + Strong base
H3CO
H
H3CO
H
HO
H
alkoxide oxonium ionalcohol
Alcohol Nomenclature• Parent chain = longest chain containing C with -OH
• Root name: replace –e with –ol• ethane ethanol, butene butenol, etc.
• Give –OH the smallest possible number• –OH has priority over double bonds, alkyl groups
• Two –OH groups -diol; three –OH groups -triol– Add to end of root name (propane propanediol)
OH
5-methyl-3-hexanol
OHHO
1,2-ethanediol(ethylene glycol)
antifreeze
Alcohol Naming Practice
OH
OH
OH
OH
OH
2-propanol
(isopropyl alcohol)2,4-dimethyl-3-pentanol
4-penten-2-ol3,5-dimethyl-2,4-heptanediol
Classes of Alcohols
Primary (1°) alcohol
Secondary (2°) alcohol
Tertiary (3°) alcohol
OH
OH
OH
CH3
1-butanol
4-phenyl-2-hexanol
1-methylcyclohexanol
OH C attached to 1 other C
OH C attached to 2 other C’s
OH C attached to 3 other C’s
Reactions of Alcohols• Reaction with strong bases
– alcohol as proton donor (weak acid)
• Reaction with strong acids– alcohol as proton acceptor (weak base)
• Dehydration– reverse of hydration of alkenes
– requires H+ catalyst
• Oxidation– increase # of C-O bonds
R OH R O
H
H
R O
Strong acid
Strong base
alkoxide
oxonium ion
R OH
- H2O
alkene
H C C CH3
OH
H
H
H
C C
CH3
HH
H
R R'
O
R H
O
aldehyde ketone
orR OH
oxidizing agent
H+
Dehydration MechanismStep 1: electrophilic H+ catalyst attacks nucleophilic O atom
Step 2: H2O dissociates, leaving behind a carbocation
Step 3: Electrons from neighboring C-H bond form bond, regenerating H+ catalyst
H2O+H C C CH3
O
H
H
H
HH
H C C
H
H
CH3
H
H C C
H
H
CH3
HC C
CH3
HH
H
H+
H C C CH3
O
H
H
H
HH
H C C CH3
OH
H
H
H
H
Hydration and Dehydration
C C
CH3
HH
H
H2O+ H C C CH3
OH
H
H
H
H+
Hydration and dehydration are in equilibrium
Can change [H2O] to favor one reaction or the other
Change Favors
Increase [H2O] Formation of Alcohol (hydration)
Decrease [H2O] Formation of Alkene (dehydration)
Possible Dehydration Products
The most-substituted alkene product is favored (most stable)
OH
H
OH
H
OHH
OHH+
?
Majorproduct
Least H’s on double bond
Oxidation of Alcohols• Oxidation: increases oxidation number
– More C-O bonds (add O) or increases bond order– Fewer C-H bonds (remove H)
• Needs an oxidizing agent– CrO3, Cr2O7
2-, MnO4-
1° alcohol
RC
H
O
RC
OH
OC OHR
H
H
aldehyde carboxylic acid
PCC stops ataldehyde
oxidizingagent
oxidizingagent
+1
+1
-1-2
+1
+1
-2 -2
-2+3+1
+1
0
0 0
CrO3
(Cr6+)Cr3+
,or PCC (pyridinium chlorochromate)
Breathalyzer Tests
ethanol ethanal(acetaldehyde)
ethanoic acid(acetic acid)
CH3 C OH
H
H
CH3 C
H
O
CH3 C
OH
O
+ Cr6+ + Cr3+
oxidized oxidized
Breathalyzer Tests
ethanol ethanal(acetaldehyde)
ethanoic acid(acetic acid)
CH3 C OH
H
H
CH3 C
H
O
CH3 C
OH
O
+ Cr6+ + Cr3+
oxidized oxidized
methanol methanal(formaldehyde)
methanoic acid(formic acid)
H C OH
H
H
H C
H
O
H C
OH
Ooxidized oxidized
RC
R
OC OHR
H
R
Oxidation of Alcohols
2° alcohol
ketone
oxidizingagent
C OHR
R
R
3° alcohol oxidizingagent No reaction
-2+1
0
-2
+20
0
0 0
+1
CH3 C
CH3
O
CH3 C OH
CH3
H
2-propanol propanone(acetone)
Reaction of Alcohols with Hydrogen Halides
1° alcohols react via the SN2 reaction mechanism:
C OH + HX C X + H2O
2° and 3° alcohols react via SN1 reaction mechanism: