Introduction to organic chemistry

New Way Chemistry for Hong Kong A-Level Book 3Acompounds obtained from living organisms Inorganic compounds Inorganic compounds obtained from non-living sources Development of Organic C

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New Way Chemistry for Hong Kong A-Level Book 3A1

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Introduction to Organic Chemistry

21.1 What is Organic Chemistry?

21.2 The Unique Nature of Carbon 21.3 Classification of Organic Compounds 21.4 Factors Affecting the Physical Properties of

Organic Compounds

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New Way Chemistry for Hong Kong A-Level Book 3A

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21.

Organic Chemistry?

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Organic Chemistry

• Chemistry of the compounds present

in living organisms

• They all contain carbon.

• Organic Chemistry is the Chemistry

of Carbon

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Living things

Carbohydrates / Proteins / Fats / Vitamins /

Antibiotics

Natural Sources of Organic Compounds

A variety of organic products obtained from living things

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Crude oil

or coal

Fractional distillation / destructive distillation

Alkanes / Alkenes / Alkynes / Aromatic hydrocarbons

Natural Sources of Organic Compounds

A variety of useful products derived from crude oil and coal

Check Point 21-1

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compounds

obtained from living organisms

Inorganic compounds Inorganic

compounds

obtained from non-living sources

Development of Organic Chemistry

as a Science

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(Inorganic compound) compound) (Organic

In 1828, Wohler (a German chemist)

as a Science

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Redefining …

Organic chemistry is the study of carbon

hydrogencarbonates, carbides and

cyanides) obtained from natural sources or synthesized in the laboratories.

Organic chemistry is the study of carbon compounds (except CO, CO 2 , carbonates,

hydrogencarbonates, carbides and

cyanides) obtained from natural sources or synthesized in the laboratories.

as a Science

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Ability to form four strong strong covalent bonds covalent bonds

Carbon (ground state)

• Electronic configuration of carbon (ground state) : 1s 2 2s 2 2p 2

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• Each carbon atom has four unpaired

electrons when excited

• Tend to form four strong covalent bonds

Carbon (excited state)

Ability to form four strong strong covalent bonds covalent bonds

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• Carbon atoms link together to form

chains of varying length, branched chains and rings of different sizes

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Carbon (excited state)

Ability to Form Multiple Bonds

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Single bond Double bond Triple bond

* X = halogens

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Example 21-2 Check Point 21-2

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21.

of Organic Compounds

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• Organic compounds are classified by

the the presence of characteristic functional groups.

Functional Groups

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Functional Groups

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Functional Groups

• Propane does not react with sodium

• Ethanol and propan-1-ol react with

sodium to give hydrogen gas

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• have similar chemical properties

 they contain the same functional group –OH

 they are classified into the same

homologous series — alcohols

and

Functional Groups

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Homologous Series

A homologous series is a series of compounds that have the same functional group, and each member differs from

their formulae.

A homologous series is a series of compounds that have the same functional group, and each member differs from

the next member by a – CH 2 – unit in their formulae.

CH 4 C 2 H 6 C 3 H 8 C 4 H 10

CH 2 CH 2 CH 2

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formula

Structural formula

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formula

Structural formula

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• Members in the same series can be represented by a general formula e.g alkanes: C n H 2n+2

alkenes: C n H 2n

alkynes: C n H 2n-2

Homologous Series

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Functional group

of an organic compound

Chemical properties

Members of a homologous series have similar chemical properties

Homologous Series

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• The physical properties change gradually

along the homologous series

• e.g the longer the carbon chain in the

molecule ( or the greater the molecular mass)

 the greater the attractive force

between molecules

 the higher the melting point,

boiling point and density

Homologous Series

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State (at room temperature

and pressure)

Melting point (°C) point (°C) Boiling

Density of solid / liquid at 20°C (g cm–3)

–183 –172 –188 –135 –130 –95 –91 –57 –54 –30

–161 –89 –42 0 36 69 98 126 151 174

– – – – 0.626 0.657 0.684 0.703 0.718 0.730

Some physical properties of the first 20 members of

straight-chain alkanes

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and pressure)

Melting point (°C)

Boiling point (°C)

Density of solid / liquid at 20°C (g cm–3)

–26 –10 –7 –3 10 18 22 28 32 37

196 216 233 260 271 287 302 316 330 344

0.740 0.749 0.753 0.761 0.769 0.773 0.778 0.777 0.777 0.785

Some physical properties of the first 20 members of

straight-chain alkanes

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Example 21-3A Example 21-3B

Example 21-3C Check Point 21-3

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Organic Compounds

Refer to notes on ‘Bonding and Structure’

pp.77-92 – intermolecular forces

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1 Structure of the functional group

1.1 Dipole moment of the molecule 1.2 Formation of hydrogen bonding

2 Length of carbon chains (London

dispersion forces)

Main Factors Affecting the Physical Properties of Organic Compounds

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• Molecules having a polar functional

group have a higher b.p than others with a non-polar functional group of similar molecular masses

 Stronger intermolecular attraction

among molecules

Structure of Functional Group

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Structure of Functional Group

Molecule Relative

molecular mass

groups

CH3CH2CH2CH3 58 -0.5

CH3CH2CH = CH2 56 -6.2

CH3CH2C ≡ CH 54 8.1

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Dipole Moment of Molecule

• Tetrachloromethane has 4 polar bonds

in the molecule

• M.p and b.p are very low

 the molecule is non-polar

 the molecule is tetrahedrally

symmetrical

 the dipole moments of the

C  Cl bond cancel each other

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Examples of Polar Molecules

with Net Dipole Moment

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Examples of Non-polar Molecules with No Net Dipole Moment

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Solubility of Organic Molecules

• Depends on the polarity of organic

molecules and the solvent

• Non-polar or weakly polar compounds

dissolve readily in non-polar or weakly polar solvents

• Highly polar compounds dissolve readily

in highly polar solvents

• “Like dissolves like”

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Solubility of Organic Molecules

Hexane in tetrachloromethane Hexane in water

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Why does Hexane Dissolve Readily in Tetrachloromethane?

Intermolecular forces among

hexane molecules and those

among tetrachloromethane

molecules

≈

Intermolecular forces between hexane and tetrachloromethane

molecules

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Why is Hexane Insoluble in Water?

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Formation of Hydrogen Bonding

• Molecules having  OH or  NH 2 groups

are able to form hydrogen bonds

• Hydrogen bonds affect the physical

properties of alcohols and amines with

low molecular masses

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Why does Propan-1-ol have a

Higher Boiling Point?

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Formation of Hydrogen Bonding

• Also affect the solubility of a molecule

• Molecules with  OH groups are able

to form hydrogen bonds with surrounding water molecules

 Soluble in water

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Example 21-4A

Example 21-4B

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Length of Carbon Chains

• Molecules with higher molecular masses

have higher m.p., b.p and density

 Higher molecular masses

 Large molecular sizes

 Stronger London dispersion

forces among molecules

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• Molecules with branched chains

 b.p and density lower than its

straight-chain isomer

 Straight-chain isomers have greater

surface area in contact with each other

 Greater attractive force among the

molecules

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• Molecules with branched chains

 m.p higher than its straight-chain

isomer

 Branched-chain isomers are more

spherical

 Packed more efficiently in solid state

 Extra energy is needed to break down the efficient packing

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Example 21-4C

Check Point 21-4

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Family General formula Functional group

Example Formula IUPAC name

Alkane RH (Nil) CH3CH3 Ethane

Alkene

RCH = CH2RCH = CHR

R2C = CHR

R2C = CR2

carbon double bond

Carbon-CH2 = CH2 Ethene

Alkyne RC ≡ CH

RC ≡ CR

– C ≡ C – Carbon- carbon triple bond

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Ester

ester group

Methyl ethanoate

Acyl halide

acyl halide group

Ethanoyl chloride

Amide

amide group

Ethanamide

R = CnH2n+1 –

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R = CnH2n+1 –

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(a)How was organic chemistry defined

(a) The knowledge of organic and inorganic

compounds was raised during the 1780s

Scientists defined organic chemistry as the study of compounds that could be obtained from living organisms They believed that the synthesis of organic compounds took place in living organisms only.

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many organic compounds can be synthesized from inorganic substances The updated

definition of organic chemistry is the study of carbon compounds, except for carbon

monoxide, carbon dioxide, carbonates, hydrogencarbonates, carbides and cyanides

These compounds have been traditionally classified under inorganic chemistry.

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Why is carbon able to catenate?

Back

Answer The ability to catenate of carbon is chiefly due to

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Would you expect silicon, which is just below

carbon in the Periodic Table, to catenate to form diverse molecular structures? Explain your

Silicon, unlike carbon, does not catenate to form diverse

molecular structures Carbon is able to catenate because

carbon atoms have a relatively small atomic size This

enables a carbon atom to form strong covalent bonds

with other carbon atoms However, due to the greater

atomic size of silicon, its ability to catenate is much lower

than that of carbon.

Back

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has only two unpaired electrons Its atomic size is larger than that of carbon So it has a much lower tendency to catenate than carbon.

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( )

Back

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Back

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State whether each of the following pairs of

compounds belongs to the same homologous series Explain your answer.

(a)

Answer (a) No, the first one is a carboxylic acid and the

second one is an ester.

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(b)

Answer (b) Yes, both of them are alcohols.

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(c)

Answer (c) No, the first one is an amide and

the second one is an amine.

Back

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(a) Name the homologous series of organic

carboxylic acid, ester, acyl halide, amide and acid anhydride

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(b) Identify and name the functional groups in

glucose which has the following structure.

Answer

group)

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(c) Identify and name the functional groups in

the following compounds:

Answer

Back

(aldehyde), (acyl chloride), (carbon-carbon double bond) groups

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Why is oil immiscible with water?

Answer

so they cannot form hydrogen bonds with water molecules.

Back

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The relative molecular mass of glucose is 180.0, but it

is soluble in water Why?

Answer

they are able to form hydrogen bonds with

water molecules Therefore, glucose is

soluble in water despite it has a high

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Despite the fact that butan-1-ol and

ethoxyethane have the same relative molecular mass, they have very different boiling points The boiling points of butan-1-ol and

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able to form hydrogen bonds with one another and the energy required to separate butan-1-ol molecules would be much greater Whereas for

ethoxyethane, the attraction among the molecules is weak van der

Waals’ forces only The amount of energy required to break the forces would not be great Therefore, the boiling point of ethoxyethane is lower than that of butan-1-ol.

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