introduction to organic chemistry

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

Introduction to Organic Chemistry

24.124.1 What is Organic Chemistry?What is Organic Chemistry?

24.224.2 The Unique Nature of CarbonThe Unique Nature of Carbon

24.324.3 Classification of Organic CompoundsClassification of Organic Compounds

Chapter 24Chapter 24


24.1 What is Organic Chemistry (SB p.2)

Organic Chemistry: The chemistry of the compounds of carbon

Carbon compounds: DNA, proteins in our body, carbohydrates, wool, cotton, petrol, medicines, pesticides, etc.

Organic chemicals

• make our life easy

• but also cause serious environmental problems

(e.g. organic compounds used as aerosol propellent damage the ozone layer, insecticide is harmful to human



Development of Organic Chemistry as a ScienceDevelopment of Organic Chemistry as a Science

In the past …,ChemistryChemistry

Organic Compounds

Organic Compounds

obtained from living

organisms

Inorganic CompoundsInorganic

Compounds

obtained from non-living sources


(Inorganic compound) (Organic compound)

In 1828, Wohler (a German chemist)

Redefining …...

Organic chemistry is the study of carbon compounds except carbon monoxide, carbon dioxide, carbonates, hydrogencarbonates, carbides and cyanide.

Organic chemistry is the study of carbon compounds except carbon monoxide, carbon dioxide, carbonates, hydrogencarbonates, carbides and cyanide.




Natural Sources of Organic CompoundsNatural Sources of Organic Compounds

Crude oil / coal

Fractional distillation / destructive distillation

Alkanes / Alkenes / Alkynes / Aromatic hydrocarbons

Living things Carbohydrates / Proteins / Fats / Vitamins / Antibiotics


24.2 The Unique Nature of Carbon (SB p.5)

Ability to CatenateAbility to Catenate

Carbon atoms can link themselves together to form chains of varying length, branched chains and rings of different sizes

Catenation:The ability of atoms in forming stable bonds with itself and joining up in chains or rings.

e.g.



Ability to Form Multiple BondsAbility to Form Multiple Bonds

• Each carbon atom has four unpaired electrons when excited

• tend to form 4 covalent bonds

Carbon (ground state)

Carbon (excited state)

• Electronic configuration of carbon (ground state) : 1s22s22p2



Single bond Double bond Triple bond


Example 24-1Example 24-1Would you expect silicon, which is just below carbon in the Periodic Table, to catenate to form diverse molecular structures? Explain your answer.

Answer


Solution:

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.


Check Point 24-1 Check Point 24-1

Would you expect sulphur, which has an electronegativity value very close to carbon, to catenate? Why?

Answer

The electronic configuration of sulphur is 1s22s22p63s23p4. It has only two unpaired electrons. Its atomic s

ize is larger than that of carbon. So it has a much low

er tendency to catenate than carbon.



24.3 Classification of Organic Compounds (SB p.7)

Functional GroupsFunctional Groups

The compounds in a particular family are characterized by the presence of a certain arrangement of atoms called a functional group

A functional group is defined as an atom or a group of atoms that effectively determines the chemical properties of an organic compound.

A functional group is defined as an atom or a group of atoms that effectively determines the chemical properties of an organic compound.


have similar chemical properties because they contain the same functional group –OH. They are classified into the same homologous series — Alcohols.

e.g.

and




FamilyGeneral formula

Functional group

Specific example

Formula IUPAC name

Alkane RHC – H and C – C bonds

CH3CH3 Ethane

Alkene

RCH = CH2

RCH = CHR

R2C = CHR

R2C = CR2

CH2 = CH2 Ethene

AlkyneRC CH

RC CR– C C – HC CH Ethyne

Aromatic hydrocarbon

ArH Aromatic ring Benzene

Haloalkane RX CH3Cl Chloromethane

R = CnH2n+1 –




Functional group

Specific example

Formula IUPAC name

Alcohol ROH CH3OH Methanol

Ether R – O – R CH3 – O – CH3 Methoxymethane

Aldehyde Methanal

Ketone Propanone

R = CnH2n+1 –




Functional group

Specific example

FormulaIUPAC name

Carboxylic acid Ethanoic acid

Amine

RNH2

R2NH

R3N

CH3NH2 Methylamine

Nitrile RC N – C N CH3CN Ethanenitrile

EsterMethyl ethanoate

Acyl halideEthanoyl chloride

R = CnH2n+1 –, X = F, Cl, Br or I



Family General formulaFunctional

group

Specific example

FormulaIUPAC name

Amide Ethanamide

Acid anhydrid

e

Ethanoic anhydride

R = CnH2n+1 –



A homologous series is a series of compounds that have the same functional group, and each member differs from the next member by a – CH2 – unit in 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 – CH2 – unit in their formulae.

CH3CH2CH2CH3C4H10Butane4

CH3CH2CH3C3H8Propane3

CH3CH3C2H6Ethane2

CH4CH4Methane1

Structural formulaCondensed structural formula

Molecular formula

IUPAC name

Number of carbon atom(s)




IUPAC name

Molecular formula

Condensed structural formula

Structural formula

1 Methanol CH3OH CH3OH

2 Ethanol C2H5OH CH3CH2OH

3 Propanol C3H7OH CH3CH2CH2OH

4 Butanol C4H9OH CH3CH2CH2CH2OH



Members in the same series can be represented by a general formula.

e.g. General formula of alkanes: CnH2n+2

General formula of alcohols: CnH2n+1OH

Functional group of an organic compound

Chemical

properties

Members of a homologous series have similar chemical properties


The physical properties change gradually along the homologous

series

e.g. the longer the carbon chain in molecule ( or the greater the

molecular mass)

the greater the attractive force between molecules

the higher the melting point and boiling point





Molecular formula

State (at room temperature

and pressure)

Melting point (°C)

Boiling point (°C)

Density of solid / liquid at 20°C

(g cm–3)

1

2

3

4

5

6

7

8

9

10

CH4

C2H6

C3H8

C4H10

C5H12

C6H14

C7H16

C8H18

C9H20

C10H22

Gas

Gas

Gas

Gas

Liquid

Liquid

Liquid

Liquid

Liquid

Liquid

–183

–172

–188

–135

–130

–95

–31

–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




Molecular formula

State (at room temperature

and pressure)

Melting point (°C)

Boiling point (°C)

Density of solid / liquid at 20°C

(g cm–3)

11

12

13

14

15

16

17

18

19

20

C11H24

C12H26

C13H28

C14H30

C15H32

C16H34

C17H36

C18H38

C19H40

C20H42

Liquid

Liquid

Liquid

Liquid

Liquid

Liquid

Liquid

Solid

Solid

Solid

–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


Example 24-2Example 24-2Identify the functional group(s) in the following compound:

(a)

Answer


Solution:

(a) Carbon-carbon double bond ( ) and chloro ( ) group



(b)

Answer


Solution:

(b) Carbonyl group ( )



(c)

Answer


Solution:

(c) Amino group ( ) and carboxyl

group ( )


Example 24-3Example 24-3To which homologous series does each of the following compounds belong?

(a)

Answer


Solution:

(a) Ester



(b)

Answer

Solution:

(b) Amide




(c)

Answer

Solution:

(c) Acid anhydride



Example 24-4Example 24-4State whether each of the following pairs of compounds belongs to the same homologous series. Explain your answers.

(a)

AnswerSolution:

(a) No, the first one is a carboxylic acid and the second one is an ester.




(b)

AnswerSolution:

(b) Yes, both of them are alcohols.




(c)

AnswerSolution:

(c) No, the first one is an amide and the second one is an amine.




(a) Name the homologous series of organic compounds that contain the element oxygen in their functional groups.

Answer

(a) Alcohol, ether, aldehyde, ketone, carboxylic acid,

ester, acyl halide, amide and acid anhydride




(b) Identify and name the functional groups in glucose which has the structure:

Answer


(b) – OH (hydroxyl) and – O – (oxy) groups



(c) Identify and name the functional groups in the following compound:

Answer


(c) – Br (bromo), (aldehyde),

(acyl chloride) and

(carbon-carbon double bond) group


The END

introduction to organic chemistry

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