introduction to organic chemistry chapter 19 introduction to organic chemistry chapter 19 hein and...

Introduction to Organic Chemistry

Chapter 19

Introduction to Organic Chemistry

Chapter 19

Hein and Arena (modified 5-06 with a couple of corrections 08)

Eugene PasserChemistry DepartmentBronx Community College

© John Wiley and Sons, Inc.

Version 1.0

This power point is from the old text. The Prentice Hall text is chapter 22-23. The content you are expected to know for ch. 22-23 is the Organic Molecules Lab and the worksheet that follows this power point (ch. 22 worksheet)

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Chapter Outline19.2 The Carbon Atom

19.3 Hydrocarbons

19.4 Alkanes19.13 Alkyl Halides

19.14 Alcohols19.5 Structural Formulas and

Isomerism

19.6 Naming Alkanes

19.12 Hydrocarbon Derivatives

19.15 Naming Alcohols

19.16 Ethers

19.7 Alkenes and Alkynes

19.8 Naming Alkenes and Alkynes

19.11 Naming Aromatic Compounds

19.9 Reactions of Alkenes

19.10 Aromatic Hydrocarbons

19.17 Aldehydes and Ketones

19.18 Naming Aldehydes and Ketones

19.19 Carboxylic Acids

19.20 Esters

19.21 Polymers–Macromolecules

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Organic Chemistry

The branch of chemistry that deals with carbon compounds.

– fats, proteins, carbohydrates

– fabrics

– wood and paper products

– plastics

– medicinals

4

Sources of Organic Compounds

Carbon-containing raw materials– petroleum and natural gas

– coal

– carbohydrates

– fats and oils

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The Carbon Atom

The Carbon Atom

6

12 136 6 Carbon has two stable isotopes C and C.

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Carbon has several radioactive isotopes.

The C isotope is used in radiocarbon

dating.

• The carbon atom is central to all organic compounds.

7

Carbon has four valence electrons

1s2, 2s2, 2p2

C

8

C

Carbon forms four single covalent bonds by sharing electrons with other atoms.

H

HH H

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CH

HH H

Carbon forms four single covalent bonds by sharing electrons with other atoms.

10

CH

HH H

The bonds between carbon and other atoms are often drawn at right angles.

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Actually the angle between the bonds is 109.5o

19.1 c

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19.1 a

The bonds point to the corners of a tetrahedron.

19.1 b

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19.1 a

The bonds point to the corners of a tetrahedron.

19.1 d

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Space filling models.

19.2

16

One covalent bond can be formed between two carbon atoms. C C

single bond

A dash represents a covalent bond.

17

One covalent bond can be formed between two carbon atoms.

single bond

C C

18

Two covalent bonds can be formed between two carbon atoms. C C

double bond

19

Two covalent bonds can be formed between two carbon atoms.

double bond

C C

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Three covalent bonds can be formed between two carbon atoms. C C

triple bond

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Three covalent bonds can be formed between two carbon atoms.

triple bond

C C

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Long chains of carbon atoms form by linking one carbon atom to another through covalent bonds.

CC

CC

CC

Cseven carbon chain

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CC

CC

CC

C

C

Cnine carbon chain

C C

Long chains of carbon atoms form by linking one carbon atom to another through covalent bonds.

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CC

CC

CC

C

C

Cnine carbon branched chain

Long chains of carbon atoms form by linking one carbon atom to another through covalent bonds.

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HydrocarbonsHydrocarbons

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• Hydrocarbons are compounds composed entirely of carbon and hydrogen atoms bonded to each other by covalent bonds.

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• Saturated hydrocarbons have only single bonds between carbon atoms.

• Unsaturated hydrocarbons contain a double or triple bond between two carbon atoms.

• Aromatic hydrocarbons include benzene and all compounds resembling benzene.

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19.3

carbon to carbon single bonds

carbon to carbon double bonds

carbon to carbon triple bonds

This is not the chart to copy for ch. 22 worksheet

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AlkanesAlkanes

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• Alkanes are also known as paraffins or saturated hydrocarbons.

• They are straight- or branched-chain hydrocarbons.

• There are only single covalent bonds between the carbon atoms of alkanes.

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• Each member of a homologous series differs from the next member by a CH2

group.

• The members of a homologous series are similar in structure but differ in formula.

• Successive members in the alkane series differ from each other by one carbon and two hydrogen atoms. They form a homologous series.

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The general formula of alkanes is CnH2n+2

n = 7

2 x 7 + 2 = 16

C7H16This is the chart you copy for the ch. 22 ws

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Structural Formulas and Isomerism

Structural Formulas and Isomerism

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• Structure means the way in which the atoms bond within the molecule.

• The properties of an organic substance are dependent on its molecular structure.

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• Each carbon atom is joined to four other atoms by covalent bonds.

• These bonds are separated by angles of 109.5o.

• Alkane molecules are essentially nonpolar.

• Alkane molecules contain only carbon-carbon and carbon-hydrogen bonds.

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Ccarbon has 4 bonds Nnitrogen has 3 bondsoxygen has 2 bonds Ohydrogen has 1 bond HIiodine has 1 bondchlorine has 1 bond Clbromine has 1 bond BrFfluorine has 1 bond

The majority of organic compounds are made from relatively few molecules: carbon, hydrogen, oxygen, nitrogen and the halogens.

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Structures of Common Alkanes

Structures of Common Alkanes

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C

H

HH

H

line structure form of

methane

CH4

space filling form of

methane

There is 1 possible structure for CH4.

19.419.4

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CH3CH3

line structure form of ethane

C

H

CH

H

H

H

H

space filling form of ethane

There is 1 possible structure for C2H6.

19.4

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line structure form of propane

C

H

CH

H

C

H

H

H

H

H

space filling form of propane

CH3CH2CH3

There is 1 possible structure for C3H8.

19.4

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C C CC

H

H

H H

H

HH

H

H

H

line structure form of butane

CH3CH2CH2CH3space filling

form of butaneThere are 2 possible structures for C4H10

unbranched chain19.4

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C C C

C

H

H

H

H H

HH

H H

H

line structure form of 2-methyl

propane

CH2CHCH3

CH3

branched chain

space filling form of 2-methyl

propane

branched chain

There are 2 possible structures for C4H10.

19.4

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normal butane (n-butane) C4H10

2 –methyl propane

C4H10

C C CC

H

H

H H

H

HH

H

H

H

C C C

C

H

H

H

H H

HH

H H

H

m.p. 0.5oC

b.p. –138.3oC

m.p. –159.5oC

b.p. – -11.7oC

Normal butane and 2-methyl propane are isomers.

Isomers are compounds with the same molecular formula but different structural formulas.

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Pentane (C5H12) has 3 isomers.

This is the carbon skeleton with the longest continuous carbon chain. It is the first isomer of pentane.

C C C C C

n-pentane

C C C C C

H

H

H

H

H

H

HH

H

H

H

H

Hydrogen is added to each carbon to form four bonds.

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Pentane (C5H12) has 3 isomers.

2-methylbutane

To form the next isomer write a four carbon chain.

C C C CC C C C

C

Add the fifth carbon atom to either of the middle carbon atoms.

C C C C

C

Hydrogen is added to each carbon to form four bonds.

C C C C H

CH

H

H

H

HHH

H

H

H

H

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Pentane (C5H12) has 3 isomers.

2,2-dimethylpropane

To form the third isomer write a 3 carbon chain.

C C C

Add the remaining two carbon atoms to the central carbon atom.

C C C

C

C

Hydrogen is added to each carbon to form four bonds.

C C C

C

C

HHH

HHH

H

H

H

H

H

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Condensed structural formulas are often used to save time and space.

In a condensed structural formula the atoms and groups attached to a carbon atom are written to the right of that carbon atom.

C C CC

H

H

H H

H

HH

H

H

Hstructuralformula

CH3CH2CH2CH3

condensedstructural formula

C C C

C

H

H

H

H H

HH

H H

H

CH2CHCH3

CH3

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Naming AlkanesNaming Alkanes

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• The general formula of an alkyl group is CnH2n+1.

• Alkyl groups are used to name organic compounds.

The corresponding alkane has the formula

CnH2n+2

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R= CnH2n+1 (any alkyl group)

R = CH3 — methyl group

R = CH3CH2 — ethyl group

The letter “R” is often used in formulas to represent any of the possible alkyl groups.

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The naming of organic compounds is now done in accordance with the IUPAC system.

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Alkenes and AlkynesAlkenes and Alkynes

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• They contain fewer than the maximum number of hydrogens.

• Alkynes have four fewer hydrogen atoms than an alkane.

• Alkenes and alkynes are unsaturated.

• Alkenes have two fewer hydrogen atoms than an alkane.

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Alkenes contain a carbon-carbon double bond.

Alkynes contain a carbon-carbon triple bond.

General formula for alkenes: CnH2n

General formula for alkynes: CnH2n-2

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19.5

Alkene Alkyne

double bond

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19.5

Alkene Alkyne

triple bond

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NamingAlkenes and Alkynes

NamingAlkenes and Alkynes

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Reactions of AlkenesReactions of Alkenes

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• This greater reactivity is due to the carbon-carbon double bonds.

• Addition at the carbon-carbon double bond is the most common alkene reaction.

• Alkenes are more reactive than their corresponding alkanes.

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Addition Reactions

Addition of bromine to 2-penteneBromine adds across the double bond.

2,3-dibromopentane

double bond breaks saturated

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Addition Reactions

Addition of hydrogen chloride to 1-butene

2-chlorobutane

Hydrogen chloride adds across the double bond.

double bond breaks saturated

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Aromatic Hydrocarbons

Aromatic Hydrocarbons

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• Aromatic originally referred to the pleasant odor of these molecules, but this meaning has been dropped.

• Benzene and all substances with structures resembling benzene are classified as aromatic compounds.

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• Its molecular formula is C6H6

• The determination of a structural formula for benzene was difficult.

• Benzene was discovered in 1825 by Michael Faraday.

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• In 1865 August Kekulé proposed that the carbon atoms in a benzene molecule are arranged in a six-membered ring with one hydrogen atom bonded to each carbon atom and with three carbon-carbon double bonds.

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benzene space filling model

benzene Kekulé structure

3 double bonds

6 carbons in a ring

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Benzene does not react like an alkene.

C6H6 + Cl2 → C6H5Cl + HClFe

Chlorine substituted for a hydrogen.

Instead of addition reactions it undergoes substitution reactions.

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Benzene is a hybrid of these two Kekulé structures.

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The corner of each hexagon represents a carbon and a hydrogen atom.

The structure of benzene can be represented in two abbreviated ways.

CH

CH

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Naming Aromatic Compounds

Naming Aromatic Compounds

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• A monosubstituted benzene has the formula C6H5G where G is the group that replaces a hydrogen atom.

• All hydrogens in benzene are equivalent.

• It does not matter which hydrogen is replaced by G.

• A substituted benzene is derived by replacing one or more of benzene’s hydrogen atoms with an atom or group of atoms.

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Monosubstituted BenzenesMonosubstituted Benzenes

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• Some monosubstituted benzenes are named by adding the name of the substituent group as a prefix to the word benzene.

• The name is written as one word.

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nitrobenzene

nitro group

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ethylbenzene

ethyl group

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• Certain monosubstituted benzenes have special names.

• These are parent names for further substituted compounds.

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methyl group

toluene

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hydroxy group

phenol

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carboxyl group

benzoic acid

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amino group

aniline

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• C6H5— is the phenyl group.

• It is used to name compounds that cannot be easily named as benzene derivatives.

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diphenylmethane

4-phenyl-2-pentene

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Disubstituted BenzenesDisubstituted Benzenes

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• Three isomers are possible when two substituents replace hydrogen in a benzene molecule.

• The prefixes ortho-, meta- and para- (o-, m- and p-) are used to name these disubstituted benzenes.

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ortho-dichlorobenzene(1,2-dichlorobenzene)mp –17.2oC, bp 180.4oC

ortho disubstituted benzene

substituents on adjacent carbons

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meta-dichlorobenzene(1,3-dichlorobenzene)mp –24.82oC, bp 172oC

meta disubstituted benzene

substituents on adjacent carbons

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para-dichlorobenzene(1,4-dichlorobenzene)mp 53.1, bp 174.4oC

para disubstituted benzene

substituents are on opposite sides of the benzene ring

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phenolnitrophenol

When one substituent corresponds to a monosubstituted benzene with a special name, the monosubstituted compound becomes the parent name for the disubstituted compound.

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When one substituent corresponds to a monosubstituted benzene with a special name, the monosubstituted compound becomes the parent name for the disubstituted compound.

toluenem-nitrotoluene

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Hydrocarbon Derivatives

Hydrocarbon Derivatives

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• Hydrocarbon derivatives are compounds that can be synthesized from a hydrocarbon.

• In addition to carbon, they contain such additional elements as oxygen, nitrogen, or a halogen.

• The compounds can be grouped into several classes. The compounds in each class have similar properties.

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AlkylHalidesAlkyl

Halides

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• An alkyl halide has the formula RX where X = Cl or Br.

• They are formed in a substitution reaction in which a halogen replaces hydrogen.

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RH + X2 → RX + HXuv

light

When a specific halogen is used the name reflects this: chlorination

CH3CH3 + Cl2 → CH3CH2Cl + HCluv

light

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AlcoholsAlcohols

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• Alcohols are organic molecules whose molecules contain the –OH functional group.

• The general formula for alcohols is ROH.

100

• Alcohols do not dissociate in water yielding OH- as do metallic hydroxides.

• The –OH group is attached to the carbon by a covalent bond and not an ionic bond as in metallic hydroxides.

• Alcohols are classified as primary (1o), secondary (2o) or tertiary (3o).

• Alcohols form a homologous series.

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Primary Alcohol

The carbon to which the – OH group is attached is bonded to one carbon.

103

Secondary Alcohol

The carbon to which the –OH group is attached is bonded to two carbons.

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Tertiary Alcohol

The carbon to which the –OH group is attached is bonded to three carbons.

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19.6

106

• Alcohols that contain more than one OH group attached to different carbons are called polyhydroxy alcohols.

Polyhydroxy Alcohols

• Monohydroxy: one OH group per molecule.

• Dihydroxy: two OH groups per molecule.

• Trihydroxy: three OH groups per molecule.

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Naming AlcoholsNaming Alcohols

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EthersEthers

110

• An ether has the formula ROR´.

• R and R´ can be the same or different groups.

• R and R´ can be saturated, unsaturated or aromatic.

• Saturated ethers have little chemical reactivity but are often used as solvents.

111

• Alcohols and ethers are isomeric.

• They have the same molecular formula but different structural formulas.

• An alcohol and its isomeric ether have different chemical and physical properties.

112

CH3CH2OH

ethanolB.P. 78.3oC

hydrogen bondssoluble in water

C2H6O

CH3–O–CH3

dimethyl etherB.P. –27.3oC

does not hydrogen bondinsoluble in water

C2H6O

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Naming EthersNaming Ethers

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Common Names

Common names of ethers are formed from the names of the groups attached to the carbon atom in alphabetical order followed by the word ether.

CH3CH2CH2 — O — CH2CH3

propyl ethyl

ethyl propyl ether

ether

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Aldehydesand KetonesAldehydes

and Ketones

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carbonyl groupcarbon is

double bonded to the oxygen

Aldehydes and ketones contain

the carbonyl group.

117

Aldehydes have at least one hydrogen bonded to the carbonyl group. The other group bonded to the carbonyl group is an alkyl (R) or aromatic (Ar) group.

118

Ketones have two alkyl (R) or aromatic (Ar) groups bonded to the carbonyl group.

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Naming Aldehydesand Ketones

Naming Aldehydesand Ketones

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Naming AldehydesNaming Aldehydes

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The IUPAC names of aldehydes are obtained by dropping the –e and adding -al to the name of the parent hydrocarbon.

butane butanal al

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Naming KetonesNaming Ketones

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• The IUPAC name of a ketone is derived from the name of the alkane corresponding to the longest carbon chain that contains the ketone-carbonyl group.

• The parent name is formed by changing the –e ending of the alkane to -one.

propane propanone one

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Carboxylic AcidsCarboxylic Acids

125

carbonyl group

Carboxylic acids contain the carboxyl group.

OH bonded to a carbonyl

carbon.

126

The carboxyl group can also be written as

or

127

• Open-chain carboxylic acids form a homologous series.

• The carbonyl group ( ) is always at the beginning of a carbon chain.

• The carbonyl carbon atom is always designated as C-1.

3 2 1

128

• The IUPAC name of a carboxylic acid is derived from the name of the alkane corresponding to the longest carbon chain that contains the carboxyl group.

• The parent name is formed by changing the –e ending of the alkane to –oic acid.

methanone oic acid methane

129 propanone oic acid

• The IUPAC name of a carboxylic acid is derived from the name of the alkane corresponding to the longest carbon chain that contains the caroxyl group.

• The parent name is formed by changing the –e ending of the alkane to –oic acid.

propane

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• Organic acids are usually known by common names.

• These names usually refer to a natural source of the acid.

ethanoic acid

IUPAC name

acetic acid

common name

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• Organic acids are usually known by common names.

• These names usually refer to a natural source of the acid.

methanoic acid

IUPAC name

formic acid

common name

132

• This is the simplest aromatic acid.

benzoic acid

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134

EstersEsters

135

carbonyl group

OR´ bonded to a carbonyl

carbon.

An ester is an organic compound derived from a carboxylic acid and an alcohol.

The ester functional group is –COOR.

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Polymers-Macromolecules

Polymers-Macromolecules

138

• A polymer (macromolecule) is a natural or synthetic giant molecule formed from smaller molecules (monomers).

• Monomers are the small units that undergo polymerization to form a polymer.

• Polymerization is the process of forming very large, high molar-mass molecules from monomers.

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Formation of Polyethylene

nCH2=CH2 → CH2 CH2[CH2 CH2]n CH2 CH2 CH2 CH3

ethylene monomerpolyethylene

• n = the number of monomer units.

• n ranges from 2,500 to 25,000

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