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Structures of Alcohols, Phenols, Thiols and Ethers

Alcohols, phenols, thiols and ethers consist of ahydrocarbon singly bonded to an oxygen or a sulfur

Alcohols have an -OH group attached to an alkane, phenolshave an -OH group attached to a benzene, thiols have an-SH group attached to an alkane and ethers have an Obonded to two Cs

OH

SH

OH

O

Alchol Phenol

Thiol Ether

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Naming Alcohols Parent name ends in -ol

Find longest chain containing the C to which the OHgroup is attached Number Cs starting at end nearest OH group Locate and number substituents and give full name

- use a number to indicate position of OH group- cyclic alcohols have cyclo- before the parent name;numbering begins at the OH group, going indirection that gives substituents lowest possiblenumbers- use a prefix (di-, tri-) to indicate multiple OHgroups in a compound

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Nomenclature

Ethanol(Ethyl alcohol)

1-Propanol(Propyl alcohol)

2-Propanol(Isopropyl alcohol)

1-Butanol(Butyl alcohol)

OH

OH

OHOH

2-Butanol(sec -Butyl alcohol)

2-Methyl-1-propanol(Isobutyl alcohol)

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

OH

Cyclohexanol(Cyclohexyl alcohol)

OHOH

OH

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Naming Phenols Phenol is the common name for an OH group

attached to a benzene, and is accepted by IUPAC Compounds with additional substituents are

named as substituted phenols Ortho , meta and para are used when there is only

one other substituent If there are two or more additional substituents,

each must be numbered, beginning at the OH and

going in direction that gives substituents lowestnumbers (or alphabetical if same in bothdirections)

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Many phenols have pleasant odors, and some are bioactive- Euganol (from cloves) is a topical anesthetic- Thymol (from thyme) is an antiseptic

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Naming Thiols Parent name ends in -thiol Find longest chain containing the C to which the SH

group is attached Number Cs starting at end nearest SH group Parent name is alkane name of carbon portion of longest

chain, followed by thiol Locate and number substituents and give full name- use a number to indicate position of SH group- cyclic thiols have cyclo- before the parent name;numbering begins at the SH group, going in directionthat gives substituents lowest possible numbers- use a prefix (di-, tri-) to indicate multiple SH groups ina compound

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Thiols - Nomenclature

Common names for simple thiols arederived by naming the alkyl group bondedto -SH and adding the word " mercaptanmercaptan "

CH 3 CH 2 SH

CH 3

CH 3 CHCH 2 SHEthanethiol

(Ethyl mercaptan)2-Methyl-1-propanethiol

(Isobutyl mercaptan)

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Naming Ethers Simple ethers are named by their common names

For common names: name each alkyl groupattached to the oxygen followed by ether For complex ethers IUPAC names are used For IUPAC names:

1. Name as an alkane, with larger alkyl groupbeing the parent chain2. The smaller alkyl group and the O are namedtogether as an alkoxy group (replace -yl with -oxy)3. Number chain starting at end nearest alkoxygroup4. Use a number to give location of alkoxy group

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OCH 3CH 3 CH 2 OCH 2 CH 3

Cyclohexyl methyl ether(Methoxycyclohexane)

Diethyl ether

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Naming Cyclic Ethers

Cyclic ethers are generally named by their common names(we will not study the IUPAC names)

A cyclic ether containing two carbons is called ethyleneoxide (generally known as epoxides)

A cyclic ether containing 4 carbons (with 2 double bonds)is called a furan

A cyclic ether containing 5 carbons (with 2 double bonds)is called a pyran A cyclic ether containing 4 carbons and 2 oxygens is

called a dioxane

O

O

furan

O O

O

1,4-dioxane

O

O

ethylene oxide tetrahydrofuran pyran tetrahydropyran

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Naming Examples

OH

SH

OH OH

CH 3

OH

BrBrO

O

O

O

2-propanol 2-ethyl-4-methylcyclopentanol propanethiol ortho -methylphenol

2,4-dibromophenol diethyl ether furan 1,4-dioxane

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Physical Properties of Alcohols, Phenols, Thiols and Ethers All of these types of compounds have a bent geometry around the

O or the S, and are polar compounds

Alcohols and phenols contain a very polarized O-H bond, and theycan H-bond with themselves and with other alcohols or water

- Small alcohols (4 or less Cs) are soluble in water- Phenol is soluble in water (even with 6 Cs) because it partiallyionizes in water (its a weak acid)

- Alcohols and phenols have relatively high boiling points Thiols are much less polar than alcohols because the

electronegativity of S is the same as that of C (2.5), much less thanthat of O (3.5), so C-S and S-H bonds are not polar

- thiols do not H-bond and have relatively low boiling points Ethers do not H-bond with themselves, so have boiling points

similar to hydrocarbons-ethers are only slightly soluble in water and are highly flammable

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Physical Properties bp increases as MW increases solubility in water decreases as MW increases

CH 3 CH 2 CH 2 OH

CH 3 CH 2 CH 2 CH 3

CH 3 OH

CH 3 CH 3

CH 3 CH 2 OH

CH 3 CH 2 CH 3

CH 3 CH 2 CH 2 CH 2 OH

CH3

CH2

CH2

CH2

CH3

Structural Formula NameMolecular

Weightbp

(C)Solubilityin Water

methanol 32 65 infiniteethane 30 -89 insolubleethanol 46 78 infinitepropane 44 -42 insoluble

1-propanol 60 97 infinitebutane 58 0 insoluble

8 g /100 g117741-butanolpentane

72 36 insoluble

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Acidity and Basicity of Alcohols and Phenols Alcohols and phenols, like water, can act as either weak acids or weak

bases (although phenol is more acidic) Phenols are more acidic because the anion that forms upon loss of the

proton is stabilized by resonance

O

H+HCl

O

H

H

+ Cl

O

H+ NH 3

O + NH 4

O

H

+ H 2 O

O

+ H 3 O

O O O O

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Combustion Reactions of Alcohols and Ethers

Both alcohols and ethers can burn with oxygen toproduce water, carbon dioxide and heat (just likehydrocarbons)

However, ethers are much more flammable thanalcohols and care should be taken when working withethers in the laboratory (just a spark from static

electricity can set off ether fumes)

Examples:

CH 3CH 2OH + 3O 2 2CO 2 + 3H 2O + Heat

CH 3-O-CH 3 + 3O 2 2CO 2 + 3H 2O + Heat

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Dehydration of Alcohols to Form Alkenes An alcohol can lose a water molecule to form an alkene using an acid

catalyst such as H 2 SO 4 and heat (an elimination reaction) This is the reverse of the addition of H 2 O to an alkene Dehydration is favored by using heat (endothermic reaction) and a

solvent other than water (lower concentration of H 2 O) When more than one alkene can be formed, Zaitsevs rule states that

the more substituted alkene will be the major product Order of reactivity = 3 > 2 > (1 > methyl)

- In fact this reaction only works with 3 and 2 alcohols

+

Heat

H3O+

+Heat

H3O+

CH 3

+ H2O

+ H2O

OH

H

OH

H

CH 3

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