Chemistry 121(01) Winter 2010-11 Chapter 14: …upali/chem121/slides/chapter-14...1 Chemistry 121, Winter 2011, LA Tech 14-1 Introduction to Organic Chemistry and Biochemistry InstructorDr.

1

14-1Chemistry 121, Winter 2011, LA Tech

Introduction to Organic Chemistry and Biochemistry

Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)

E-mail: [email protected]

Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;

Office Hours: MWF 8:00 am - 10:00 am;

TT 9:00 – 10:00 am & 1:00-2:00 pm.

December 17, 2010 Test 1 (Chapters 12-13)

January 19, 2011 Test 2 (Chapters 14,15 & 16)

February 7, 2011 Test 3(Chapters 17, 18 & 19)

February 23, 2011 Test 4 (Chapters 20, 21 & 22)

February 24, 2011 Comprehensive Make Up Exam:

Chemistry 121(01) Winter 2010-11


Chapter 14: Alcohols, Phenols, and Ethers14.1 Bonding Characteristics of Oxygen Atoms in Organic Compounds

14.2 Structural Characteristics of Alcohols

14.3 Nomenclature for Alcohols

14.4 Isomerism for Alcohols

14.6 Physical Properties of Alcohols

14.7 Preparation of Alcohols

14.8 Classification of Alcohols

14.9 Chemical Reactions of Alcohols

14.11 Structural Characteristics of Phenols

14.12 Nomenclature for Phenols

14.13 Physical and Chemical Properties of Phenols

14.15 Structural Characteristics of Ethers

14.16 Nomenclature for Ethers

14.18 Physical and Chemical Properties of Ethers

14.20 Sulfur Analogs and Alcohols

14.21 Sulfur Analogs of Ethers

Menthol: A Useful Naturally Occurring Terpene Alcohol; Ethers as General

Anesthetics; Marijuana: The Most Commonly Used Illicit Drug; Garlic and

Onions: Odiferous Medicinal Plants


Oxygen and Sulfur are Group VIA Elements

Has 6 valance electrons

• Two lone pairs

• Two bonding pairs, i.e., it can form two

covalent bonds

• Two single or one double bond

Oxygen and Sulfur


• Carbon forms four bonds

• Hydrogen forms one bond

• Oxygen and sulfur forms two bonds.

C

4 Valence Electrons4 Covalent bonds

No nonbonding pairs

H O

1 Valence Electron1 Covalent bonds

No nonbonding pairs

6 Valence Electrons2 Covalent bonds

2 nonbonding pairs

Bonding in organic compounds with O and S

2


Alcohol: An organic compound in which an —

OH group is bonded to a saturated carbon

atom.

Saturated carbon atom: A carbon atom that is

bonded to four other atoms.

General structure: R-OH (OH is functional

group)

• Examples: CH3OH, C3H7OH

• OH in alcohols is not ionic as in NaOH.

Alcohols


Alcohols, and Ethers Structures

Functional groups:

alcohol: R-O-H

phenols: Ar-OH

ether: R-O-R'

thiol: R-S-H

Alkyl, R = CH3 Mehtyl etc.


Common Names for Alcohols

Common names for Alcohols (C1-C4 alkyl

groups).

− Rule 1: Name all of the carbon atoms of the

molecule as a single alkyl group.

− Example: Methyl (C1), Ethyl (C2), propyl (C3) butyl (C4)

− Rule 2: Add the word alcohol, separating the

worlds with a space.

− Examples:

CH3 OH CH3 CH2 OH CH3 CH2 CH2 OH

CH3 CH OH

CH3

OH

Methyl alcohol Ethyl alcohol Propyl alcohol

Isopropyl alcohol Cyclobutyl alcohol


IUPAC Nomenclature of compounds

containing functional groups

The IUPAC system deals with functional groups two

different ways.

Modification of the hydrocarbon name to indicate the

presence of a functional group.

alcohol, -OH use -ol ending.

ether: CH3CH2-O-CH3 use methoxy methoxy

ethane

thiol: R-S-H use -thiol ending.

3


Alcohol example

C - C - C - C - O - H

Base contains 4 carbon

- alkane name is butane

- remove -e and add -ol

alcohol name - butanol

OH is on the first carbon so -

1-butanol


Alcohols - Nomenclature

Unsaturated alcohols

• the double bond is shown by the infix -en-

• the hydroxyl group is shown by the suffix -ol

• number the chain to give OH the lower number

52

OH1346

trans-3-hexene-1-ol(E)-3-hexene-1-ol


Alcohols are classified as primary (1o),

secondary (2o), or tertiary (3o) alcohols

Primary alcohol (1o): Hydroxyl-bearing carbon

atom is bonded to only one other carbon

atom.

Secondary alcohol (2o): Hydroxyl bearing

carbon atom is bonded to two other carbon

atoms.

Tertiary alcohol (3o): Hydroxyl-bearing carbon

atom is bonded to three other carbon atoms.

Reactions are dependent on the type of alcohol

Alcohols Classification


Classification of alcohols

Primary

Secondary

Tertiary.

4



Examples:

Ethanol(Ethyl alcohol)

1-Propanol(Propyl alcohol)

2-Propanol(Isopropyl alcohol)

1-Butanol(Butyl alcohol)

OH

OH

OH

OH

2-Butanol

(sec-Butyl alcohol)2-Methyl-1-propanol

(Isobutyl alcohol)

2-Methyl-2-propanol(t ert-Butyl alcohol)

OH

Cyclohexanol(Cyclohexyl alcohol)

OH

OH

OH



Problem: Write the IUPAC name of each alcohol

OH

CH3 ( CH2 )6 CH2 OH

OH

(a)

(b)

(c)

Octanol

4-methyl-2-pentanol

2-isopropyl cyclohexanol


Common names

Ethyl alcohol

ethylene glycol

glycerol


DiolsA diol with two -OH groups attached on two

adjacent carbon atoms.

Colorless, odorless, miscible in water, great

antifreeze, airplane deicer.

Extremely toxic.

Ethylene Glycol (1,2-Ethanediol)

Propylene Glycol (1,2-Propanediol)

is nontoxic and is used in drugs as solvent.

CH2 CH2

Ethylene glycol

OH OH

CH2 CH2 CH2

OH

Propylene glycol

OH

5


Intramolecular Alcohol Dehydration

Production of Alkene

A dehydration reaction in which the

components of water (-H and -OH) are

removed from a single reactant

Also known as an elimination reaction

CH3 CH CH2

OHH

H2SO4

180oC

CH3 CH CH2 + H2O


Alcohol Dehydration

In an intramolecular alcohol dehydration, the

components of water (-H and -OH) are

removed from neighboring carbon atoms

with the resultant introduction of a double

bond into the molecule.


Intramolecular Alcohol Dehydration

Dehydration of an alcohol can result in more

than one alkene product, because hydrogen

loss can occur from either of the neighboring

carbon atoms.

Example: Dehydration of 2-butanol produces

two alkenes.

• Zaitsev’s rule can be used determine the

dominant product.

OH

2-Butanol

H2SO4

180oC+ H2O+

1-Butene 2-Butene


Zaitisev’s Rule

The major product formed in an

intramolecular alcohol dehydration reaction

is the alkene that has the greatest number of

alkyl groups attached to the carbon atoms

of the double bond.

• In the following reaction, the predominant

product will be 2-butene because the product

has CH3 attached to each carbon atom.

OH

2-Butanol

H2SO4

180oC+ H2O+

1-Butene 2-Butene(Predominant)

6


Intermolecular Alcohol Dehydration

In this reaction, two molecules of alcohol

combine to form an ether (Condensation

reaction)

• Only true for primary alcohols and 140oC.

• Secondary and tertiary alcohols always give

alkene.

HO

H

H

H

H2SO4

140 oC

+ H2O

H

H

HH

H

O

H

2


Oxidation

Addition of oxygen or removal of hydrogen

Mild Oxidizing Agents: KMnO4, K2Cr2O7,

H2CrO4

Primary and Secondary Alcohols can be

oxidized by mild oxidizing agents

R'C

H

OH

RKMnO4

R R'

O

+ 2H


Reactivity of 1ry, 2ry and 3ry alcohols:

OH

1-propanol

OH

2-butanol

HO

2-methyl-2butanol

O

propaldehyde

O

OH

propionic acid

(O)(O)

O

2-butanone

(O)

(O)

No Reaction

Oxidation of Alcohols


Halogenation

Alcohols undergo halogenation reactions

In this reaction a halogen atom is substituted

for the hydroxyl group producing an alkyl

halide.

Alkyl halide production by this reaction is

superior to alkyl halide production through

halogenation of an alkane

R OH + PX3 R-X + H3PO43 3

CH3CH2OH + CH3CH2Cl + H3PO4PCl3 33

(PX3: X is Cl or Br)

7


Constitutional isomerism is possible for

alcohols containing three or more carbon

atoms.

Two types of isomers

• Skeletal isomers

• Positional isomers


Alcohol molecules have both polar and

nonpolar character.

• The hydroxyl group is polar part of the molecule

• The alkyl (R) group is nonpolar part of the

molcule

The physical properties depend on which

portion of the structure ―dominates.‖

• Length of the nonpolar carbon chain

• Number of polar hydroxyl groups

Physical Properties


Physical Properties

Alcohols are polar compounds

• both the C-O and O-H bonds are polar covalent

-

+

+O

HH

H

C

H


Hydrogen Bonding

• Figure shows the association of ethanol molecules in

the liquid state (only two of the three possible

hydrogen bonds to the upper oxygen are shown here).

8


Boiling Points

Alcohols have higher boiling points and are more soluble

in water than hydrocarbons

CH3CH2 CH2OH

CH3CH2 CH2CH3

CH3OH

CH3CH3

CH3CH2 OH

CH3CH2 CH3

CH3CH2 CH2CH2CH2OH

HOCH2CH2CH2CH2 OH

CH3CH2 CH2CH2CH2CH3

Structural Formula Name

Molecular

Weight

(g/mol)

BoilingPoint

(°C)Solubilityin Water

methanol 32 65 infinite

ethane 30 -89 insoluble

ethanol 46 78 infinite

propane 44 -42 insoluble

1-propanol 60 97 infinite

butane 58 0 insoluble

1-pentanol 88 138 2.3 g/100 g

1,4-butanediol 90 230 infinite

hexane 86 69 insoluble


Boiling Points and Solubilities in Water (of selected 1-alcohols)


Combustion reactiond of alcohol

Like other hydrocarbons alcohols are also

flammable.

The combustion products are carbon dioxide

and water.

2 CH3OH + 4O2 2CO2 + 4 H2O


Conversion of ROH to RX

• water-soluble 3° alcohols react very rapidly with HCl,

HBr, and HI

• low-molecular-weight 1° and 2° alcohols are unreactive

under these conditions

CH3COH

CH3

CH3

HCl CH3 CCl

CH3

CH3

H2 O

2-Chloro-2-methylpropane

2-Methyl-2-propanol

25°C+ +

9


Reaction with SOCl2Thionyl chloride, SOCl2, is the most widely used

reagent for conversion of alcohols to alkyl

chlorides

OH SOCl2

Cl SO2 HCl

Thionylchloride

1-Heptanol

1-Chloroheptane

pyridine+

+ +


Dehydration of Alcohols

An alcohol can be converted to an alkene by

elimination of H and OH from adjacent carbons (a

-elimination)

• 1° alcohols must be heated at high temperature in the

presence of an acid catalyst, such as H2SO4 or H3PO4

• 2° alcohols undergo dehydration at somewhat lower

temperatures

• 3° alcohols often require temperatures only at or

slightly above room temperature


Dehydration of Alcohols

• examples:

140oC

Cyclohexanol Cyclohexene

OH

+ H 2 OH2 SO4

180oCCH3 CH2 OH

H2 SO4CH2 =CH 2 + H 2 O

+ H2 OCH3 COH

CH3

CH3

50oC

H2 SO4CH3 C= CH2

CH3

2-Methylpropene

(Isobutylene)


Hydration-Dehydration

Acid-catalyzed hydration of an alkene and

dehydration of an alcohol are competing

processes

• large amounts of water favor alcohol formation

• scarcity of water or experimental conditions where

water is removed favor alkene formation

An alkene An alcohol

C C

H OH

H2O

acidcatalyst

+C C

10



• to oxidize a 1° alcohol to an aldehyde, use PCC

• PCC oxidation of geraniol gives geranial

Tertiary alcohols are not oxidized by either of these

reagents; they are resistant to oxidation

CrO3 HCl

N N

H

CrO3Cl-

Pyridinium chlorochromate (PCC)

Pyridine

+ +

+

OHPCC

CH2 Cl2H

O

Geraniol Geranial


Acidity of Alcohols

• pKa values for several low-molecular-weight alcohols

(CH3 )3COH

(CH3 )2CHOH

CH3 CH2OH

H2O

CH3 OH

CH3 COOH

HCl

Compound pKa

-7

15.5

15.7

15.9

17

18

4.8

hydrogen chloride

acetic acid

methanol

water

ethanol

2-propanol

2-methyl-2-propanol

Structural Formula

Stronger acid

Weaker acid

*Also given for comparison are pKa values for water,

acetic acid, and hydrogen chloride.


Reaction with Active Metals

Alcohols react with Li, Na, K, and other active

metals to liberate hydrogen gas and form metal

alkoxides

• Na is oxidized to Na+ and H+ is reduced to H2

• alkoxides are somewhat stronger bases that OH-

• alkoxides can be used as nucleophiles in nucleophilic

substitution reactions

• they can also be used as bases in -elimination

reactions

2CH3 CH2 OH 2Na 2CH3 CH2 O-Na

+ H2+ +

Sodium ethoxide


Conversion of ROH to RX

Conversion of an alcohol to an alkyl halide involves

substitution of halogen for -OH at a saturated

carbon

• the most common reagents for this purpose are the

halogen acids, HX, and thionyl chloride, SOCl2

11


Prepared by hydration of alkenes

Alkenes react with water (an

unsymmetrical addition agent) in the

presence of sulfuric acid (the catalyst)

to form an alcohol

Markovnikov’s rule is used to determine

the predominant alcohol product

Preparation of Alcohols




Oxidation of a 1° alcohol gives an aldehyde or a

carboxylic acid, depending on the oxidizing agent

and experimental conditions

• the most common oxidizing agent is chromic acid

• chromic acid oxidation of 1-octanol gives octanoic acid

CrO3 H2OH2SO4 H2CrO4+

Chromic acidChromium(VI)oxide

CH3 (CH2 )6CH2OHCrO3

H2SO4 , H2OCH3 (CH2 )6CH

O

CH3 (CH2 )6COH

O

Octanal(not isolated)

Octanoic acid1-Octanol


• Addition of H2 to carbonyl (C=O, ).

• It is similar to adding H2 to a double bond.

• In this case one of hydrogen will be added to carbon and the

other to oxygen atom of C=O.

O

CR

O

R' + H2C

H

R' OHR

R = H: AldehydeR = R: Ketone

Addition of H2 to carbonyl (C=O)

12

14-45Chemistry 121, Winter 2011, LA Tech 14-46Chemistry 121, Winter 2011, LA Tech

14-47Chemistry 121, Winter 2011, LA Tech 14-48Chemistry 121, Winter 2011, LA Tech

It is possible to synthesize polymeric alcohols

with structures similar to those of

substituted polyethylenes

The simplest polymer is polyvinyl alcohol

(PVA)

• PVA is a tough, whitish polymer that can from

strong films,

• tubes, and fibers that are highly resistant to

hydrocarbon solvents

• Unlike most organic polymers, PVA is water-

soluble

Polyvinyl alcohol (PVA)

13


Phenol: An organic compound in which an —OH group

is attached to a carbon atom that is part of an

aromatic carbon ring system

Aryl group: An aromatic carbon ring system from which

one hydrogen atom has been removed.

General formula for an aryl alcohol: Ar-OH

Substituted phenols: Aryl group substituted with other

groups like CH3, NO2 , etc.OH

phenol

OH

H3C

Cl

Substituted phenol

Phenols

Phenyl, Ar = C6H5

4-chloro-3-methyl phenol


Phenols: Name ―Phenol‖ is approved by IUPAC

• Assign the position of the substituent followed by

its name and the word phenol

• Carbon atom with -OH is always number 1 and

the other substituents will be assigned minimum

possible numbers with reference to hydroxyl

carbon

HO

phenol

OHBr

3-bromophenol

HO

H3C

2-methylphenol

IUPAC names of Phenols


Phenols

The functional group of a phenol is an -OH group

bonded to a benzene ring

1,2-Benzenediol(Catechol)

1,4-Benzenediol(Hydroquinone)

3-Methylphenol(m- Cresol)

Phenol

OH OHOHOH

OH

CH3

OH


Phenols

• some phenols

OH

OH

OH

OCH3 OH

OH

Hexylresorcinol Eugenol Urushiol

OHCHO

OH

OCH3

2-Isopropyl-5-methylphenol(Thymol)

4-Hydroxy-3-methoxybenzaldehyde(Vanillin)

14


Acidity of Phenols

Phenols are significantly more acidic than alcohols

pKa = 9.95OH O-

Phenol Phenoxide ion

+ H2 O + H3 O+

CH3 CH2 OH H2 O CH3 CH2 O- H3 O+

pKa = 15.9

Ethanol Ethoxide ion

+ +


Phenols :

• Low-melting solids or oily liquids at room

temperature.

• Sparingly soluble in water

• Many phenols have antiseptic and disinfectant

properties.

The simplest phenol: phenol

• A colorless solid with a medicinal odor

• Melting point: 41oC

• More soluble in water than any other phenols

Properties of Phenols


Acidity of Phenols

Unlike alcohols, phenols are weak acids in

solution.

As acids, phenols have Ka values of about 10-10 M.

OH

+ H2O

O-

+ H3O+

Phenol Phenoxide Ion


Phenols have antiseptic properties

• 4-hexylresorcinol is an ingredient in many

mouthwashes and throat lozenges.

• o-phenylphenol and 2-benzyl-4-chlorophenol are

the active ingredients in Lysol, a disinfectant.

Antiseptic Properties of Phenols

15


Phenols have antioxidant properties: BHA

(butylated hydroxy anisole) and BHT

(butylated hydroxy toluene) are used as food

preservatives to protect it from air oxidation

• Vitamin E is a phenolic antioxidant

A number of phenols found in plants are used

as flavoring agents and/or antibacterials.

Vanillin is a phenolic which gives flavor of

vanilla

Antioxidant Properties of Phenols


Ethers: Oxygen bonded to two carbon atoms

(functional group)

• General formula: R-O-R

• Examples:

• CH3-O-CH3, CH3-O-C2H5

• Water and ether have similar structure in that two

H of water are replaced by R groups in ethers

Ethers


Name the two hydrocarbon groups attached to

oxygen atom of the ether and add the word

ether

• The hydrocarbon groups are listed in alphabetical

order

• When both R groups are same than di is used

with the name of R group

• Examples:

O

ethyl methyl ether

O

butyl ethyl ether

O

dimethyl ether

Earlier ―common‖ naming of ethers


Naming Ethers

2-propoxybutane

2-methoxyphenol

ethoxycyclopropane

isopropyl propyl ether

methyl phenyl ether

16


Ethers - Nomenclature

IUPAC • the longest carbon chain is the parent alkane

• name the -OR group as an alkoxy substituent

Common names:

• name the groups bonded to oxygen followed by the word ether

CH3

CH3

CH3OCCH3

O Et 2O

OH

OEt

Eth oxyethane

(Diethyl eth er)

2-Methoxy-2-methylpropane(methyl t ert -buty l ether, MTBE)

t rans-2-Ethoxycyclohexanol


Ethers - Nomenclature

Although cyclic ethers have IUPAC names, their

common names are more widely used

Ethylene

oxide

Tetrahydro-

furan, THF

Tetrahydro-

pyran

1,4-Dioxane

O O

O

OO


Ethers - Physical Properties

Ethers are polar molecules

• each C-O bond is polar covalent

• however, only weak attractive forces exist between

ether molecules



• boiling points are lower than those of alcohols

CH3CH2 OH

CH3OCH3

CH3CH2 CH2CH2CH2OH

HOCH2CH2CH2CH2 OH

CH3CH2 CH2CH2OCH3

CH3CH2 CH2CH2OH

CH3CH2 OCH2CH3

CH3OCH2CH2OCH3 ethylene glycoldimethyl ether

90 84 infinite

8 g/100 g3574diethyl ether

1-butanol 74 117 7.4 g/100 g

slight7188butyl methyl ether

infinite230901,4-butanediol

2.3 g/100 g138881-pentanol

7.8 g/100 g-2446dimethyl ether

infinite7846ethanol

Solubilityin Water

BoilingPoint

(°C)Molecular

WeightNameStructural Formula

17



• ethers are hydrogen bond donors



• the effect of hydrogen bonding is illustrated by

comparing the boiling points of ethanol and dimethyl

ether

CH3CH2OH CH3OCH3

bp -24°C

Ethanol

bp 78°C

Dimethyl ether


Reactions of Ethers

Ethers resemble hydrocarbons in their resistance

to chemical reaction

• they do not react with strong oxidizing agents such as

chromic acid, H2CrO4

• they are not affected by most acids and bases at

moderate temperatures

Because of their good solvent properties and

general inertness to chemical reaction, ethers are

excellent solvents in which to carry out organic

reactions


Ethers have carbon chains (two alkyl groups )

therefore the constitutional isomerism

possibilities in ethers depend on:

1. The partitioning of carbon atoms between the two

alkyl groups, and

2. Isomerism possibilities for the individual alkyl

groups present.

• Isomerism is not possible for a C2 or a C3 ether

• C4 and C5 ethers exhibit constitutional isomers.

Isomerism in Ethers

18


Functional Group Isomerism

Ethers and alcohols with the same number of

carbon atoms and the same degree of

saturation have the same molecular formula.− For example: Dimethyl ether, and ethyl alcohol both have

the molecular formula C2H6O (constitutional isomers).

Functional group isomers are constitutional

isomers that contain different functional

groups.− C3 ether–alcohol functional group isomerism possibilities

are three (see below)

CH3 CH2 O CH3

Ethyl methyl ether

CH3 CH2 CH2 OH

CH3 CH OH

CH3

Propyl alcohol Isopropyl alcohol


Chemical properties

Ethers are Flammable, e.g., Diethyl ether has

boiling point of 35oC and therefore a flash-

fire hazard.

Ethers react slowly with oxygen from the air to

form unstable hydroperoxides and

peroxides.

Unreactive towards acids, bases and oxidizing

agents (useful for organic reactions)

Like alkanes, ethers also undergo halogenation

reactions


Cyclic ethers: Contain the ether functional groups as part of a ring

system (heterocyclic organic compounds).

Heterocyclic organic compound: a cyclic organic compound in

which one or more of the carbon atoms in the ring have been

replaced with atoms of other elements.

Important cyclic ethers:

• THF : Useful as a solvent in that it dissolves many organic

compounds and yet is miscible with water.

• Polyhydroxy derivatives of the five-membered (furan) and

six membered (pyran) carbohydrates are cyclic ether

systems

O O OTetrahydrofuran

(THF) Furan Pyran

Cyclic ethers


R-SH ---- Thiol

R-S-R ---- Thioether

Lower boiling point than corresponding

alcohols due to lack of hydrogen bonding

Strong disagreeable odor

Natural gas odor is due to added thiols

Thiols and Thiolethers

19


Thiols are named in the same way as alcohols

in the IUPAC system, except that the ―–ol‖

becomes ―-thiol. ‖

The prefix thio- indicates the substitution of a

sulfur atom for an oxygen atom.

As in the case of diols and triols, the ―-e‖ at the

end of the alkane name is also retained for

thiols.

CH3 CH2 CH2 SH

Propanethiol

CH3 CH CH2 CH3

SH

2-Butanethiol

Naming Thiols


Properties of Thiols

Have lower boiling points than alcohols (lack of hydrogen

bonding)

Have strong, disagreeable odor

The familiar odor of natural gas results from the addition of a low

concentration of methanethiol (CH3—SH) to the gas.

The scent of skunks is due to two thiols.

Oxidation of thiols: Lead to disulfide (S-S) bond formation

2 R-SH R-S-S-R + 2H

The above reaction is of biological importance

• Disulfide bonds formed from two —SH groups aid in protein

structure stabilization

More reactive than ethers due to weak C-S bond


Thioethers (or sulfides: An organic compound in which

a sulfur atom is bonded to two carbon atoms by

single bonds.

General formula: R—S—R.

Like thiols, thioethers (or sulfides) have strong

characteristic odors.

Thiols are more reactive than their alcohol and ether

counterparts. A carbon–sulfur covalent bond is

weaker than a carbon–oxygen bond.

Dimethyl sulfide is a gas at room temperature and ethyl

methyl sulfide is a liquid.

Thiols and thioethers exbit functional group isomerism

in the same manner that alcohols and ethers.

Thioethers and Diulfides


Naming thiols

20


Thiols - Structure

The functional group of a thiol is an -SH (sulfhydryl)

group bonded to an sp3 hybridized carbon


Thiols - Nomenclature

IUPAC names:

• the parent chain is the longest chain containing the

-SH group

• add -thiol to the name of the parent chain

Common names:

• name the alkyl group bonded to sulfur followed by the

word mercaptan

• alternatively, indicate the -SH by the prefix mercapto

Ethanethiol(Ethyl mercaptan)

2-Methyl-1-propanethiol(Isobutyl mercaptan)

2-Mercaptoethanol

SH SH HSOH


Thiols - Physical Properties

Low-molecular-weight thiols have a STENCH

CH3CH=CHCH2 SH CH3CHCH2CH2SH

CH3

3-Methyl-1-butanethiol(Isobutyl mercaptan)

2-Butene-1-thiol

Present in the scent of skunks:

CH3 -C-SH

CH3

CH3

CH3 -CH-CH3

SHNatural gas

odorants:

2-Methyl-2-propanethiol(tert -Butyl mercaptan)

2-Propanethiol(Isopropyl mercaptan)


Thiols - Physical Properties

The difference in electronegativity between S and H

is 2.5 - 2.1 = 0.4

Because of their low polarity, thiols

• show little association by hydrogen bonding

• have lower boiling points and are less soluble in water

than alcohols of comparable MW

117

78

65

1-butanol

ethanol

methanol

98

35

6

1-butanethiol

ethanethiol

methanethiol

AlcoholBoiling Point

(°C)ThiolBoiling Point

(°C)

Chemistry 121(01) Winter 2010-11 Chapter 14: …upali/chem121/slides/chapter-14...1 Chemistry 121, Winter 2011, LA Tech 14-1 Introduction to Organic Chemistry and Biochemistry InstructorDr.

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