Transcript Hess’s Law

Alcohols
H3C
O
H
• Contain a hydroxyl (-OH) group
−
R
O
O
H3C
H
H
+
H
• Intermolecular forces: dipole-dipole, H-bonding
O
H
• 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
H
R
O
alkoxide
+ Strong base
R
OH
alcohol
+ Strong acid
R
O
oxonium ion
H
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)
HO
OH
OH
5-methyl-3-hexanol
1,2-ethanediol
(ethylene glycol)
antifreeze
Alcohol Naming Practice
OH
OH
2-propanol
2,4-dimethyl-3-pentanol
(isopropyl alcohol)
OH
OH
OH
3,5-dimethyl-2,4-heptanediol
4-penten-2-ol
Classes of Alcohols
OH
1-butanol
Primary (1°) alcohol
OH C attached to 1 other C
OH
Secondary (2°) alcohol
OH C attached to 2 other C’s
4-phenyl-2-hexanol
CH3
OH
1-methylcyclohexanol
Tertiary (3°) alcohol
OH C attached to 3 other C’s
Reactions of Alcohols
• Reaction with strong bases
R
OH
Strong base
R
– alcohol as proton donor (weak acid)
• Reaction with strong acids
R
alkoxide
OH
H
– reverse of hydration of alkenes
H
– requires H+ catalyst
• Oxidation
– increase # of C-O bonds
H
Strong acid
R
oxonium ion
OH
C
C
H
H
O
H
– alcohol as proton acceptor (weak base)
• Dehydration
O
CH3
H+
- H2O
H
CH3
C
C
H
H
alkene
R
OH
oxidizing
agent
O
R
H
aldehyde
O
or
R
R'
ketone
Dehydration Mechanism
Step 1: electrophilic H+ catalyst attacks nucleophilic O atom
H
H
H
OH
C
C
H
H
CH3
H
H
H O
H
C
C
H
H
CH3
Step 2: H2O dissociates, leaving behind a carbocation
H
H
H O
H
C
C
H
H
CH3
H
H
C
CH3
C
H
H
+
H 2O
Step 3: Electrons from neighboring C-H bond form  bond,
regenerating H+ catalyst
H
H
C
H
C
CH3
H
H
CH3
C
H
C
+
H
H
Hydration and Dehydration
H
CH3
C
H
C
H+
+
H
H 2O
H
H
OH
C
C
H
H
CH3
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
OH
H+
?
H
OH
H
OH
Least H’s on
double bond
Major
product
OH
H
The most-substituted alkene product is favored (most stable)
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, Cr2O72-, MnO4-,or PCC (pyridinium chlorochromate)
PCC stops at
aldehyde
1° alcohol
+1 H
0R
-1
-2
-2
C
+1 H
OH
+1
oxidizing
agent
0R
-2
O
C
+1
H +1
aldehyde
CrO3
(Cr6+)
Cr3+
oxidizing
agent
O
+3 C
0R
-2
OH
+1
carboxylic acid
Breathalyzer Tests
H
oxidized
CH3
C
OH
oxidized
CH3
C
H
H
ethanol
+ Cr6+
O
O
CH3
C
OH
ethanal
ethanoic acid
(acetaldehyde)
(acetic acid)
+ Cr3+
Breathalyzer Tests
H
oxidized
CH3
C
OH
oxidized
CH3
C
ethanol
+ Cr6+
C
OH
ethanal
ethanoic acid
(acetaldehyde)
(acetic acid)
+ Cr3+
H
C
CH3
H
H
H
O
O
O
O
OH
H
methanol
oxidized
H
oxidized
C
H
H
C
OH
methanal
methanoic acid
(formaldehyde)
(formic acid)
Oxidation of Alcohols
0
2° alcohol
0
0
R
+1
R
-2
+1
C
OH
oxidizing
agent
-2
H
+2
0R
O
C
R0
ketone
H
CH3
O
C
CH3
OH
C
CH3
CH3
propanone
2-propanol
(acetone)
R
3° alcohol
R
C
R
OH
oxidizing
agent
No reaction
Reaction of Alcohols with Hydrogen
Halides
1° alcohols react via the SN2 reaction
mechanism:
C OH + HX
C X + H 2O
2° and 3° alcohols react via SN1 reaction
mechanism:
C C OH + HX
C C X + H2O
C
C
Reaction of Alcohols with Hydrogen
Halides
CH3OH + HBr
CH3Br + H2O
CH3CHCH3 + HCl
CH3CHCH3 + H2O
OH
Cl
Naming aldehydes and ketones
Parent chain = longest chain containing C=O (carbonyl)
Aldehyde
Ketone
oxo
oxo
Prefix
–e becomes –al
–e becomes –one
Suffix
Numbering C=O is always C #1 C=O is lowest possible number
(don’t have to number it)
(must number it)
Naming Priority: Aldehydes > Ketones > Alcohols
-OH (alcohol) substituent → “hydroxy”
OH
O
O
Cl
H
3-hydroxy-4-methylpentanal
3-chloro-2-butanone
Naming Practice
O
O
O
O
propanedial
Has both an
aldehyde and a
ketone
2,4-pentanedione
O
O
Aldehyde
has priority
Ketone = oxo
3-oxopentanal
Condensation of Alcohols
Condensation reaction: two molecules
combine to form a larger molecule (+ water)
– Catalyzed by acid (H+)
CH3−OH + H-O−CH3
alcohol
+
alcohol
H2SO4
catalyst
CH3−O−CH3 + H2O
ether
+
water
Ethers
H
R
O
O
H
H
−
water
alcohol
R
O
R
H-bond acceptor
No H-bond donor
Two alkyl groups (C’s) bound to oxygen
• Intermolecular forces:
– Dipole-dipole
– No H-bonding between ether molecules
• Lower boiling point than alcohols
– Water or alcohols can H-bond to ether oxygen
• Somewhat soluble in water and other polar solvents
Naming Ethers
• Common names: name both R groups, add “ether”
O
ethyl
ethyl
diethyl ether
(anesthetic)
Naming Ethers
• Common names: name both R groups, add “ether”
diethyl ether
(anesthetic)
O
ethyl
ethyl
tert-butyl methyl ether
(used as gasoline additive)
CH3
O
tert-butyl
methyl
O
propyl
O
O
propyl people ether
♫ “one-eyed, one-horned, flying...” ♪
Reactions of Ethers
• Formation of peroxides
peroxide
O
O
+
H
O2
O
O
diisopropyl ether
• Reactions of peroxides:
Explosive!
diisopropyl ether
peroxide
Controlled
detonation
Resulting crater:
3 feet wide,
one foot deep
Aldehydes and Ketones
O
120°
R
O
C and O both
sp2 hybridized
C
H
120°
C
R'
R
aldehyde
ketone
• C=O group called a carbonyl group
−
R
O
O
C
C
+
H
R
Very polar C=O bond
• Higher boiling point than alkanes
H
H-bond acceptor
• Soluble in polar solvents
No H-bond donor
• Lower boiling point than alcohols
Structural Isomers
• Draw all the possible structural isomers for
the following formulas:
C4H10O
C5H12O
C4H8O
C5H10O
Alcohols and Ethers
Aldehydes and Ketones
(contain a double bond)
Notice that all formulas contain one oxygen
What functional groups do you know that contain one
oxygen?
Does the atom ratio of carbon to hydrogen make a
difference?
C4H10O Isomers
OH
OH
1-butanol
2-butanol
OH
OH
2-methyl-2-propanol
O
diethyl ether
2-methyl-1-propanol
O
methyl propyl ether
O
isopropyl methyl ether
C5H12O Isomers
OH
OH
OH
2-pentanol
1-pentanol
3-pentanol
OH
HO
OH
2-methyl-1-butanol
3-methyl-2-butanol
OH
2-methyl-2-butanol
3-methyl-1-butanol
OH
2,2-dimethyl-1-propanol
C5H12O Isomers
O
butyl methyl ether
O
isobutyl methyl ether
O
tert-butyl methyl ether
O
ethyl propyl ether
O
sec-butyl methyl ether
O
ethyl isopropyl ether
C4H8O Isomers
O
O
butanal
2-butanone
O
2-methylpropanal
C5H10O Isomers
O
O
O
pentanal
2-pentanone
3-pentanone
O
O
3-methylbutanal
O
2,2-dimethylpropanal
3-methyl-2-butanone
O
2-methylbutanal
Reactions of Aldehydes and Ketones
• Oxidation of aldehydes to carboxylic acids
– CrO3, MnO4-
• Reduction of aldehydes and ketones to alcohols
– Decrease C-O bonds, increase C-H bonds
– Reducing agents: LiAlH4, NaBH4, H2/Pt
O
LiAlH4
propanal
OH
H
1-propanol
CH3−CH2−CH2−OH
CH3−CH2−CHO
O
OH
NaBH4
2-methyl-3-pentanone
2-methyl-3-pentanol
Reduction of Aldehydes/Ketones
O
OH
LiAlH4
OH
O
3-oxopentanal
1,3-pentanediol
OH
O
NaBH4
cyclohexanol
cyclohexanone
O
O
pentanedial
H2/Pt
HO
1,5-pentanediol
OH
Carboxylic Acid Nomenclature
O
R
C
• Parent chain: longest containing carboxyl group (COOH) O
H
• Name of parent: replace “–e” with “–oic acid”
• Numbering starts at carboxyl carbon
– Priority: Carboxylic acid > aldehydes > ketones > alcohols

O
O
“hydroxy”
“oxo”
substituent
substituents
OH
3-oxobutanoic acid
O
(diabetes)
O
HO
O
OH
OH
propanedioic acid
(apples)
trans-3-methyl-2-hexenoic acid
(human armpits)
OH
O
O
OH
O
HN
O
CH3
aspirin
Tylenol
Can irritate your stomach
Gentle on the stomach
A carboxylic acid
Just an alcohol
Carboxylic Acid Reactions
• Reduction to 1° alcohols
– Only LiAlH4 reduces carboxylic acids
(not NaBH4 or H2/Pt)
O
LiAlH4
butanoic acid
1-butanol
OH
OH
butanoic acid
O
NaBH4
OH
or H2/Pt
O
NO RXN
OH
Reactant remains
unchanged
What are the products?
O
O
OH
3-oxo-4-pentenoic acid
H2/Pt
NaBH4
LiAlH4
OH
O
OH
OH
O
OH
3-hydroxypentanoic acid
3-hydroxy-4-pentenoic acid
OH
OH
4-pentene-1,3-diol