Chemistry 1102Charlie BondMCS Rm 4.16/4.27Charles.Bond@uwa.edu.au

What is Organic Chemistry?Organic Reactions I IIAlkanes (Ch 21)Conformational Analysis (Ch 21)Stereochemistry I II III (Ch 22)

S

Alkyl Halides I IIII (Ch 24)Alcohols and Ether I II (Ch 24)

2Oxidation of alcoholsPrimary alcohols can be oxidised to aldehydes or carboxylic acids[O] = 1 oxidising equivalent, a generic way of describing an oxidant

Secondary alcohols can be oxidised to ketones:

[O][O]

[O]

Tertiary alcohols cannot be simply oxidised:

3Oxidation 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

Eg chromic acid oxidation of 1-octanol gives octanoic acid

CrO3 H2OH2SO4 H2CrO4+

ChromicacidChromium(VI)oxide

CH3(CH2)6CH2OHCrO3

H2SO4, H2OCH3(CH2)6CH

OCH3(CH2)6COH

O

Octanal(notisolated)

Octanoicacid1Octanol

4Oxidation of Alcohols 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 HClN N

H

CrO3Cl-

Pyridiniumchlorochromate(PCC)

Pyridine

+ ++

OHPCC

CH2Cl2 H

O

Geraniol Geranial

5Demonstrations

6Ethers - Structure

The functional group of an ether is an oxygen atom bonded to two carbon atoms oxygen is sp3 hybridized with bond angles of

approximately 109.5 in dimethyl ether, the C-O-C bond angle is

110.3

H

H O

H

C H

H

H

C

7Ethers - 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 etherether

CH3

CH3CH3OCCH3

O Et2O

OH

OEt

Ethoxyethane(Diethylether)

2Methoxy2methylpropane(methyltertbutylether,MTBE)

trans2Ethoxycyclohexanol

8Ethers - Physical Properties

Ethers are polar molecules each C-O bond is polar covalent however, only weak attractive forces exist

between ether molecules

9Ethers - Physical Properties boiling points are lower than those of alcohols

CH3CH2OHCH3OCH3

CH3CH2CH2CH2CH2OHHOCH2CH2CH2CH2OHCH3CH2CH2CH2OCH3

CH3CH2CH2CH2OHCH3CH2OCH2CH3

CH3OCH2CH2OCH3 ethyleneglycoldimethylether

90 84 infinite

8g/100g3574diethylether

1butanol 74 117 7.4g/100g

slight7188butylmethyletherinfinite230901,4butanediol2.3g/100g138881pentanol

7.8g/100g2446dimethyletherinfinite7846ethanol

SolubilityinWater

BoilingPoint(C)

MolecularWeightNameStructuralFormula

10

Ethers - Physical Properties ethers are hydrogen bond acceptors How many H-bonds can they accept?

11

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

12

Williamson Synthesis of EthersThis method of synthesising ethers brings together two parts of alkyl halide and alcohol chemistry:

the first step is the formation of an alkoxide from an alcohol:

the second step involves nucleophilic substitution on an alky halide where the alkoxide acts as the nucleophile:

13

Thiols - Structure The functional group of a thiol is an -SH

(sulfhydryl) group bonded to a tetrahedral carbon

14

Thiols - Nomenclature IUPAC names:

the parent chain is the longest chain containing the -SH group

add -thiol thiol to the name of the parent chain Common names:

name the alkyl group bonded to sulfur followed by the word mercaptanmercaptan

alternatively, indicate the -SH by the prefix mercaptomercapto

Ethanethiol(Ethylmercaptan)

2Methyl1propanethiol(Isobutylmercaptan)

2Mercaptoethanol

SH SH HS OH

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Thiols - Physical Properties

Low-molecular-weight thiols have a STENCHSTENCH

CH3CH=CHCH2SH CH3CHCH2CH2SHCH3

3Methyl1butanethiol(Isobutylmercaptan)

2Butene1thiolPresentinthe

scentofskunks:

CH3-C-SHCH3

CH3CH3-CH-CH3

SHNaturalgasodorants:

2Methyl2propanethiol(tertButylmercaptan)

2Propanethiol(Isopropylmercaptan)

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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

1177865

1butanolethanolmethanol

98356

1butanethiolethanethiolmethanethiol

AlcoholBoilingPoint

(C)ThiolBoilingPoint

(C)

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Acidity of Thiols

Thiols are stronger acids than alcohols

Thiols react with strong bases to form salts

CH3CH2SH

CH3CH2OH

H2O

H2O

CH3CH2S-

CH3CH2O- H3O+

H3O+ pKa=8.5

pKa=15.9

+

++

+

CH3CH2SH Na+OH- CH3CH2S

-Na+ H2O+ +

Strongeracid

Strongerbase

Weakerbase

Weakeracid

pKa8.5 pKa15.7

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Oxidation of Thiols

thiols are oxidized by a variety of oxidizing agents, including O2, to disulfides

disulfides, in turn, are easily reduced to thiols by several reagents

this easy interconversion between thiols and disulfides is very important in protein chemistry

2HOCH2CH2SH HOCH2CH2S-SCH2CH2OHAdisulfide

oxidation

reductionAthiol

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