alcohols structure and reactions -...

Alcohols Structure and Reactions

Alcohols Phenols Ethers Thiols Dissulfides Amines

-O- -S- -N-

OC

Alkanes Alkenes Alkynes Aromatics

Aldehydes Ketones Acids Esters Anhydrides Amides

OC-N

OC-O

Hydrocarbons

All Classes of Organic Compounds

Functionalized Hydrocarbons

Halides

F,Cl,Br O,S,N

Alcohols, Ethers, Phenols

Structure of Functional Groups


Structure of Functional GroupsThe oxygen atom in alcohols, phenols, and ethers is sp3

hybridized. Two of the sp3 orbitals are involved in bonding to hydrogen or carbon, and the remaining two contain lone-pair,

or non-bonding, electrons.

H

O

H R

O

H R

O

R’

water alcohol ether


Structure of Functional Groups

In water, the H-O-H bond angle is 104.5° due to repulsion of the bonding electron pairs by the larger non-bonding electron pairs.

In alcohols, phenols, and ethers the corresponding bond angles are closer to the expected tetrahedral 109.5° due to the replacement of one or both hydrogen atoms by larger carbon atoms.

Propyl alcohol (CH3CH2CH2OH, propanol)

Common Names

Isomerism in Alcohols

1-propanol 2-propanol

“Diols” and “Triols”

Subclassification of Alcohols

Nomenclature of Alcohols

closest to the

Nomenclature of Alcohols

12 3 4 5

Physical Properties of AlcoholsBoiling points increase with molecular weight

and decrease with branching.

Boiling points are higher than alkanes of similar molecular weight.

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

Octane, boiling point = 126 °C

Attractive forces between alkane molecules are limited to simple London forces.

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

OH H H HH

Heptanol, boiling point = 176 °C

Attractive forces between alcohol molecules include both dispersion forces and relatively strong hydrogen bonding.

Physical Properties of Alcohols-Solubility

Alcohols are more water soluble than alkanes, but their water solubility is limited by the size of the

nonpolar portion of the molecule.

CH3O

H

H3CCH2

CH2CH2

CH2CH2

CH2O

H

Nonpolar, or hydrophobic portions

of moleculesPolar, or hydrophilic portions of molecules

Physical Properties of Alcohols-Solubility

CH3

OH

CH3

OH

HO

H

THE RELATIVELY SMALL ATTRACTION BETWEENMETHANOL MOLECULES MAKES IT EASY FORWATER TO SEPARATE INDIVIDUAL METHANOL

MOLECULES FROM EACH OTHER AND DISSOLVE THE ALCOHOL.

METHANOL IS VERY SOLUBLE IN WATER.

H3CCH2

CH2CH2

CH2

CH2CH2

OH

H3CCH2

CH2CH2

CH2

CH2CH2

OH

HO

H

THE RELATIVELY LARGE ATTRACTION BETWEEN

HEPTANOL MOLECULES MAKES IT DIFFICULT FOR

WATER TO SEPARATE INDIVIDUAL HEPTANOL

MOLECULES FROM EACH OTHER AND DISSOLVE THE ALCOHOL. HEPTANOL IS VERY SLIGHTLY

SOLUBLE IN WATER.

Chemical Properties of Alcohols

Intramolecular Dehydration Reactions

C C

OH H

C C + H2O

ALCOHOL ALKENE

“H” and “OH” on adjacent carbons

?

? usually requires an acid catalyst, indicated by “H+”


Intramolecular Dehydration Reactions-Specific Examples

H C C

H

OH

H

H

H

H+ HC C

H

H

H

+ H2O

Ethanol EtheneH+

C2H6O C2H4H+

+ H2O

+ H2O


Intramolecular Dehydration Reactions-Specific Examples

H C C

H

OH

H

C

H

H

H

HH+

HC C

H

H

C

+ H2OH

HH

1-propanol, C3H8O 1-propene, C3H6

H C C

H

H

C

C

OH

H

H

HH

HH

H+

2-methyl-2-propanol, C4H10O 2-methyl-”1”-propene, C4H8

HC C

H

C

C H

HH

HH

H + H2O

Does it make any difference which H is

removed??

OH leaves


Intramolecular Dehydration Reactions-Zaitsev’s Rule

+ H2OH C C

H

H

H

OH

CH+

H

H

C

H

H

H

C4H8

C4H10O2-butanol,?

HC C

H

H

C H

CH H

HH

CC C

H

H

C H

HH

HH

H

MAJOR PRODUCTMINOR PRODUCT

If isomeric alkenes products from an alcohol dehydration, the MAJOR PRODUCT will be the alkene with the higher

number of alkyl groups attached to the double bond .

If isomeric alkenes are possible products from an alcohol dehydration, the HYDROGEN atom is lost from the carbon

with the least number of hydrogens attached.


Intermolecular Dehydration Reactions

H C C

H

H

H

O

H

H+H O C C

H

H

H

H

H

H+ + H2OH C C

H

H

H

O

H

C

H

H

C

H

H

H

C2H6O C2H6O C4H10O H2O

“H” and “OH” on two different

molecules Also called “condensation” or “dehydration synthesis”-

an extremely important reaction in biochemistry.

+ +

The reaction is run under different conditions than the

“intramolecular” dehydration.

Alcohol Worksheet

OH

OHOH

OHOH

A

B C

DE

C7H16O

C7H16O

C4H10O C5H12O

C9H18O

1.

OH

OHOH

OHOH

A

B C

DE

OH HO

O

2.

2-heptanol

C7H16O C7H14

C

C OH3C

CH3

H

H H

HC

CH3C

CH3

H

H

CC

C

OH

H

H

H

HHH C C

CH3

H

H

2-methyl-2-propanol

C4H10O C4H8

A

B

3.

CC

OH

H

HH

CC

H

H

2-ethyl-3-methyl-1-butanolC7H16O C7H14

C

CC O

H

H H

H

HC

CC

H HH

C9H18O C9H16

2-ethyl-5-methyl-cyclohexanol

D

E

3.

Chemical Properties of AlcoholsOxidation (or Dehydrogenation) Reactions

ALCOHOLALDEHYDE

or KETONE

C

O

H

H

C

O[O] H

H

Two hydrogen atoms are lost and a double bond forms between the carbon and oxygen atoms.

C

O


Oxidation of Primary Alcohols Yields Aldehydes

[O]H C C O

H

H

H

H

H H C COH

H H

[O]C C C O

H

H

H

H

H C C COH

H H

H

H

H

H

H

H

[O]C C C O

H

H

H

H

H C C COH

H H

H

H

CH

C

H

H

H

H

H

H

H

Ethanol, C2H6O Ethanal (acetaldehyde), C2H4O

1-Propanol, C3H8O Propanal (propionaldehyde), C3H6O

1-Butanol, C4H10O Butanal (butyraldehyde), C4H8O


Oxidation of Secondary Alcohols Yields Ketones

[O]C C C C

H

O

H

H

H

H

H

H

[O]C C C C

H

O

H

H

H

H

H

C

H

H

HH

H

H

C C C C

O

H

H

H

H

H

C

H

H

H

H

H

H

H

H

C C C C

O

H

H

H

H

H

H

H

H

2-butanol, C4H10O 2-butanone, C4H8O

3-pentanol, C5H12O 3-pentanone, C5H10O


Tertiary Alcohols Do Not Easily Oxidize

[O]H C C O

H

H

C

C

H

H H H

H H H

N.R. No Reaction


Oxidation (Some Details)

Oxidation of primary alcohol actually proceeds in two steps from alcohol to aldehyde to carboxylic acid.

R C O HH

HR C O H

OR C

OH

primary alcohol aldehyde carboxylic acid

In the liver, this process is catalyzed by the reaction of two sequential enzymes.


Oxidation (Some Details)

For the simple primary alcohol ethanol CH3CH2OH, the complete chemical equation (with dichromate as the reagent) can be written.

3 CH3CH2OH 2 Cr2O72- 16 H+

3 CH3COOH 11 H2O 4 Cr3+

+ +

+ +

Cr6+ Cr3+

A color change is characteristic of the reaction of dichromate with ethanol.

ethanol

acetic acid


An Application of the Oxidation Reaction

Alcohol Worksheet

HOH

OHOH

OHOH

A

B C

DE

2-heptanol

2-ethyl-3-methyl-1-butanol

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

2-ethyl-5-methyl-cyclohexanol

2º

3º 1º

1º2º

4.

2-heptanol

C7H16O C7H14O

CC

C

OH

H

H

H

HHH

CC

C

OH

H

H

HH

2,2-dimethyl-1-propanol

CH3

C CH3C

CH3

O

H

H

H

CH3

CH3C

CH3

C O

H

C5H12O C5H10O

A

C

5.

2-ethyl-3-methyl-1-butanolC7H16O

C9H18O2-ethyl-5-methyl-cyclohexanol

C9H16O

CC

OH

H

HH

CC

O

HH

C

CC O

H

H H

H

H

C

CCH2 O

H

C7H14O

D

E

5.

alcohols structure and reactions -...

Documents