Chemistry 2100

Chapter 14

ALCOHOLSETHERSTHIOLS

thiol / mercaptan(sulfhydryl)

alcohol

H

SR

ether

R'

OR

H

OR

Common Nomenclature

• alkyl "alcohol"

• dialkyl "ether"

IUPAC Nomenclature

• "e" "ol"

• locator numbers

Alcohols

Alcohol: A compound that contains an -OH (hydroxyl) group bonded to a tetrahedral carbon.– Methanol, CH3OH, is the simplest alcohol.

Nomenclature1. Select the longest carbon chain that contains the

-OH group as the parent alkane and number it from the end that gives the -OH the lower number.

2. Change the ending of the parent alkane from -e to -ol and use a number to show the location of the -OH group; for cyclic alcohols, the carbon bearing the -OH group is carbon-1.

3. Name and number substituents and list them in alphabetical order.

Nomenclature– In the IUPAC system, a compound containing two

hydroxyl groups is named as a diol, one containing three hydroxyl groups as a triol, and so forth.

– IUPAC names for diols, triols, and so on retain the final "-e" in the name of the parent alkane.

– We commonly refer to compounds containing two hydroxyl groups on adjacent carbons as glycols.CH3CHCH2

HO OHCH2CH2OH OH

CH2CHCH2

OH OHOH1,2-Ethanediol

(Ethylene glycol)1,2-Propanediol

(Propylene glycol)1,2,3-Propanetriol

(Glycerol, Glycerin)

Physical PropertiesAlcohols are polar molecules. – The C-O and O-H bonds are both polar

covalent.

Physical Properties

In the liquid state, alcohols associate by hydrogen bonding.

CH3OH 65° CH3CH2CH2OH 97°

CH3CH3 -88° CH3CH2CH2CH3 0°

CH3Cl -24° CH3CH2CH2Cl 46°

PhOH 182° CH3CH2CH2CH2OH 118°

PhCH3 110° (CH3)2CHCH2OH 108°

PhCl 132° (CH3)3COH 83°

boiling points (°C)

solubility (g / 100 mL H2O)

∞

∞

8.3

2.4

0.6

0.05

7.8

10.0

∞

3.6

CH3CH2OH

CH3CH2CH2OH

CH3CH2CH2CH2OH

CH3CH2CH2CH2CH2OH

CH3CH2CH2CH2CH2CH2OH

CH3CH2CH2CH2CH2CH2CH2CH2OH

CH3CH2OCH2CH3

(CH3)2CHCH2OH

(CH3)3COH

C6H11OH

Acidity of Alcohols

Alcohols have about the same pKa values as water.

• Aqueous solutions of alcohols have the same pH as that of pure water.– Alcohols and phenols both contain an OH group.– Phenols are weak acids and react with NaOH and

other strong bases to form water-soluble salts.

– Alcohols are weaker acids than phenols and do not react in this manner.

n

11

zymase

sucrose ethanol

2O

2O

C12H22O11 + H 4 C2H5OH + 4 CO

Preparing AlcoholsFermentation

Alkene Hydration +

H2SO 4

H OH

H2OCC C C

OHH

H

H H

H H

H H

H

DehydrationCH3CH2OH

H2SO4 CH2=CH2 H2O+Ethanol Ethylene

180°C

OHH2SO4 H2O140°C

Cyclohexanol Cyclohexene

+

CH3CCH3

OH

CH3H2SO4 CH3C=CH2

CH3

H2O50°C

2-Methyl-2-propanol (tert -Butyl alcohol)

2-Methylpropene (Isobutylene)

+

Oxidation of Alcohols

(1°)

(2°)

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

N

H H

NAD +

H+

CH3 C H

O

NAD H

Ad Ad

CH3

H

C

O

H

H

N

H

••

[O]

Ethers

Common Nomenclature

• dialkyl "ether"• dialkyl "ether"

• "alkoxy"

IUPAC Nomenclature

Physical Properties

Ethers are polar molecules in which oxygen bears a partial negative charge and each carbon bonded to it bears a partial positive charge.

Physical Properties

However, only weak forces of attraction exist between ether molecules in the pure liquid.– Consequently, boiling points of ethers are

close to those of hydrocarbons of similar molecular weight.

– Ethers have lower boiling points than alcohols of the same molecular formula.

Reactions of Ethers

Ethers resemble hydrocarbons in their resistance to chemical reaction.– They do not react with oxidizing agents such as

potassium dichromate.– They do not react with reducing agents such as H2

in the presence of a transition metal catalyst or with hydride reducing agents such as NaBH4.

– They are not affected by most acids or bases at moderate temperatures.

Because of their general inertness and good solvent properties, ethers, such as diethyl ether and THF, are excellent solvents in which to carry out organic reactions.

(diethyl) etherbp 36°C

7.8 g/100 mL

1-butanol bp 118°C

8.3 g/100 mL

pentanebp 36°C

H C C O C C H

H

H

H

H

H

H

H

H

H C C C C C H

H

H

H

H

H

H

H

H

H

H

H C C C C O H

H

H

H

H

H

H

H

H

isoflurane

F C

F

O

F

C C

Cl

H

F

F

F

halothane enflurane

F C C

F

F

Br

Cl

H

F C

H

O

F

C C

F

F

Cl

F

H

Anesthetics

p. 409

Thiols

ThiolsThiol: A compound containing an -SH (sulfhydryl group).– The most outstanding property of low-

molecular-weight thiols is their stench.– They are responsible for smells such as

those from rotten eggs and sewage.– The scent of skunks is due primarily to

these two thiols.

Naming thiols

Alkane + thiol

1-propanethiol 2-propene-1-thiol

Physical PropertiesBecause of the small difference in electronegativity between sulfur and hydrogen (2.5 - 2.1 = 0.4), an S-H bond is nonpolar covalent. – Thiols show little association by hydrogen

bonding.– Thiols have lower boiling points and are

less soluble in water and other polar solvents than alcohols of similar molecular weight.

CH3CH2OH (bp 78°C) CH3OCH3 (bp -24°C)

CH3CH2SH (bp 35°C) CH3SCH3 (bp 37°C)

[O]

R S R'

O

••

• •

• •R S R'

[O]

R S R'

O

Osulfoxidesulfide (thioether)

sulfone

Oxidation

cysteine

C OH

O

CH

NH2

CH2SH

S S S S

[H] [O]

SH

SH

SH SH

S

S

S

S

S S S S

[H] [O]

S

S

S

S

SH

SH

SH SH

[H] [O]

S

S

S

S

SH

SH

SH SH

S S S S

-helix

-helix

-helix

-helix

-helix

-helix

-helix

-helix

-helix

-pleated sheet

-helix

-helix-pleated sheet -pleated sheet

salt bridge

NH3+

-helix

-helix-pleated sheet -pleated sheet

C-O

O

hydrogen

bond

CH2 OH

CH2O

H

salt bridge NH3

+ -helix

-helix-pleated sheet -pleated sheet

C-O

O

hydrogen

bond

CH2 OH

CH2O

H

NH

H C

OH

O

hydrogenbond

salt bridge NH3

+ -helix

-helix-pleated sheet -pleated sheet

C-O

O

hydrogen

bond

CH2 OH

CH2O

H

NH

H C

OH

O

hydrogenbond

salt bridge NH3

+ CH2

HO

hydrophilicinteractionto water

CH2

C

NH2

O

CH2

HO

-helix

-helix-pleated sheet -pleated sheet

C-O

O

CH2

CH2

hydrophobicinteraction

hydrogenbond

CH2 OH

CH2O

H

NH

H C

OH

O

hydrogenbond

salt bridge NH3

+ CH2

HO

hydrophilicinteractionto water

CH2

C

NH2

O

CH2

HO

-helix

-helix-pleated sheet -pleated sheet

C-O

O

CH

CH3 CH3 CH3

CH2 CH2

hydrophobicinteraction

hydrogenbond

CH2 OH

CH2O

H

NH

H C

OH

O

hydrogenbond

salt bridge NH3

+ CH2

HO

hydrophilicinteractionto water

CH2

C

NH2

O

CH2

HO

-helix

-helix-pleated sheet -pleated sheet

C-O

O

CH

CH3 CH3 CH3

CH2 CH2

hydrophobicinteraction

S

S

S

Sdisulfide

bond

hydrogenbond

CH2 OH

CH2O

H

NH

H C

OH

O

hydrogenbond

salt bridge NH3

+ CH2

HO

hydrophilicinteractionto water

CH2

C

NH2

O

CH2

HO

-helix

-helix-pleated sheet -pleated sheet

C-O

O