Alcohols, organic chemistry

8/11/2019 Alcohols, organic chemistry

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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

H3C

O

H

HO

H

alkoxide oxonium ionalcohol


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Alcohol Nomenclature Parent chain = longest chain containing C with -OH

Root name: replacee withol ethane ethanol, butene butenol, etc.

GiveOH the smallest possible number

OH has priority over double bonds, alkyl groups

TwoOH groups -diol; threeOH groups -triol

Add to end of root name (propanepropanediol)

OH

5-methyl-3-hexanol

OHHO

1,2-ethanediol

(ethylene glycol)

antifreeze


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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


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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 Cs

OH C attached to 3 other Cs


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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+


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Hydration and Dehydration

C C

CH3

HH

H

H2O+ H C C CH3

OH

H

H

H

H+

Hydration and dehydration are in equilibriumCan change [H2O] to favor one reaction or the other

Change Favors

Increase [H2O] Formation of Alcohol (hydration)

Decrease [H2O] Formation of Alkene (dehydration)


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Possible Dehydration Products

The most-substituted alkene product is favored (most stable)

OH

H

OH

H

OHH

OHH+

?

Major

product

Least Hs ondouble bond


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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

-

1alcohol

RC

H

O

RC

OH

O

C OHR

H

H

aldehyde carboxylic acid

PCC stops at

aldehyde

oxidizing

agent

oxidizing

agent

+1

+1

-1-2

+1

+1

-2 -2

-2+3+1

+1

0

0 0

CrO3(Cr6+) Cr

3+

,or PCC (pyridinium chlorochromate)


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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


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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 COH

O

oxidized oxidized


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RC

R

O

C OHR

H

R

Oxidation of Alcohols

2alcohol

ketone

oxidizingagent

C OHR

R

R

3alcoholoxidizing

agent No reaction

-2+1

0

-2

+20

0

0 0

+1

CH3 C

CH3

O

CH3 C OH

CH3

H

2-propanol propanone

(acetone)


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Cl

O

Naming aldehydes and ketonesParent chain = longest chain containing C=O (carbonyl)

Aldehyde KetonePrefix

Suffix

Numbering

Naming Priority: Aldehydes > Ketones > Alcohols

-OH (alcohol) substituent hydroxy

oxo

e becomesal

C=O is always C #1

(dont have to number it)

oxo

e becomesone

C=O is lowest possible number

(must number it)

H

OOH

3-hydroxy-4-methylpentanal 3-chloro-2-butanone


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Naming Practice

OO

O O

O O

propanedial 2,4-pentanedione

3-oxopentanal

Has both analdehyde and a

ketone

Aldehyde

has priority

Ketone = oxo


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Condensation of Alcohols

Condensation reaction: two molecules

combine to form a larger molecule (+ water)

Catalyzed by acid (H+)

CH3OH H-OCH3

H2SO4

catalyst CH3OCH3 + H2O+

alcohol alcohol ether water+ +


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Ethers

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

RO

RR

OH

H

O

H

water

alcohol

H-bond acceptor

No H-bond donor

Two alkyl groups (Cs) bound to oxygen


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Naming Ethers

Common names: name both R groups, add ether

diethyl ether

(anesthetic)O

ethyl ethyl


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Naming Ethers

Common names: name both R groups, add ether

diethyl ether

(anesthetic)

tert- butyl methyl ether

(used as gasoline additive)

propyl people etherO

O O

O

one-eyed, one-horned, flying...

methyltert-butyl

ethyl ethyl

O

CH3

propyl


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O

O

O

H

Reactions of Ethers

Reactions of peroxides: Explosive!

Formation of peroxides

diisopropyl ether

peroxide

Controlled

detonationResulting crater:

3 feet wide,

one foot deep

+ O2

peroxide

O

diisopropyl ether
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R

C

H

O

R

C

R'

O

Aldehydes and Ketones

C=O group called a carbonylgroup

C and O both

sp2hybridized120

120

aldehyde ketone

R

CH

O

+

R

CH

OVery polar C=O bond

Higher boiling point than alkanes

H-bond acceptor

Soluble in polar solvents

No H-bond donor

Lower boiling point than alcohols


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C4H10O Isomers

OHOH

OH OH

OO

O

1-butanol 2-butanol

2-methyl-2-propanol 2-methyl-1-propanol

diethyl ether methyl propyl ether isopropyl methyl ether


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C5H12OIsomers

OH

OH

OH

OH

OH

OH

OH

OH

1-pentanol 2-pentanol 3-pentanol

2-methyl-1-butanol 3-methyl-2-butanol 3-methyl-1-butanol

2-methyl-2-butanol 2,2-dimethyl-1-propanol


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C5H12OIsomers

O O O

OOO

butyl methyl ether tert-butyl methyl ether sec-butyl methyl ether

isobutyl methyl ether ethyl propyl ether ethyl isopropyl ether


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C4H8O Isomers

O

O

O

butanal 2-butanone

2-methylpropanal

C H O I


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C5H10O Isomers

O

O

O

O

O

O

O

pentanal 2-pentanone 3-pentanone

3-methylbutanal 3-methyl-2-butanone

2,2-dimethylpropanal 2-methylbutanal


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Reactions of Aldehydes and Ketones

Oxidationof aldehydes to carboxylic acids

CrO3, MnO4-

Reductionof aldehydes and ketones to alcohols

Decrease C-O bonds, increase C-H bonds

Reducing agents: LiAlH4, NaBH4, H2/Pt

OHH

O

propanal 1-propanol

CH3CH2CHO CH3CH2CH2OH

LiAlH4

O OH

NaBH4

2-methyl-3-pentanone 2-methyl-3-pentanol


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Reduction of Aldehydes/Ketones

O

O OH

OH

O

3-oxopentanal 1,3-pentanediol

LiAlH4

NaBH4

cyclohexanone cyclohexanol

H2/Pt

OH

OO OH OH

pentanedial 1,5-pentanediol

C b li A id N l t O


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Carboxylic Acid Nomenclature

Parent chain: longest containing carboxyl group (COOH)

Name of parent: replace e with oic acid

Numberingstarts at carboxyl carbon

Priority: Carboxylic acid > aldehydes > ketones > alcohols

hydroxysubstituent

oxosubstituents

OH

O

trans-3-methyl-2-hexenoic acid

(human armpits)

OH

O O

3-oxobutanoic acid

(diabetes)

HO OH

O O

propanedioic acid

(apples)

R C

O

O H


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Carboxylic Acid Reactions

Reduction to 1alcohols

Only LiAlH4reduces carboxylic acids

(not NaBH4or H2/Pt)

butanoic acid 1-butanolOHOH

O LiAlH4

butanoic acid

OH

O NaBH4

or H2/PtNO RXN

OH

O

Reactant remains

unchanged


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What are the products?

3-oxo-4-pentenoic acid

LiAlH4

H2/Pt NaBH4

OH

OOH

OH

OO

OH

OOH

OH

OH

3-hydroxypentanoic acid

4 pentene 1 3 diol

3-hydroxy-4-pentenoic acid

Alcohols, organic chemistry

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