new way chemistry for hong kong a-level book 3a1 1 introduction to organic chemistry 21.1what is...

New Way Chemistry for Hong Kong A-Level Book 3A11

Introduction to Introduction to Organic ChemistryOrganic Chemistry

21.121.1 What is Organic Chemistry?What is Organic Chemistry?

21.221.2 The Unique Nature of CarbonThe Unique Nature of Carbon

21.321.3 Classification of Organic CompoundsClassification of Organic Compounds

21.421.4 Factors Affecting the Physical Properties of Factors Affecting the Physical Properties of

Organic CompoundsOrganic Compounds

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New Way Chemistry for Hong Kong A-Level Book 3A2New Way Chemistry for Hong Kong A-Level

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21.21.11 What is What is

Organic Organic Chemistry?Chemistry?


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21.1 What is Organic Chemistry (SB p.2)

Organic ChemistryOrganic 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 Natural Sources of Organic CompoundsCompounds

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 Natural Sources of Organic CompoundsCompounds

A variety of useful products

derived from crude oil and

coal

Check Point 21-1Check Point 21-1


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In the past …,

ChemistryChemistry

Organic compound

s

Organic compound

sobtained from

living organisms

Inorganic compound

s

Inorganic compound

sobtained from

non-living sources


Development of Organic Development of Organic Chemistry as a ScienceChemistry as a Science


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(Inorganic compound)

(Organic compound)

In 1828, Wohler (a German chemist)




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Redefining … ...Organic chemistry is the study of carbon compounds (except CO, CO2, carbonates, hydrogencarbonates, carbides and cyanides) obtained from natural sources or synthesized in the laboratories.

Organic chemistry is the study of carbon compounds (except CO, CO2, carbonates, hydrogencarbonates, carbides and cyanides) obtained from natural sources or synthesized in the laboratories.




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21.21.22 The Unique The Unique

Nature of Nature of CarbonCarbon


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

Ability to form four Ability to form four strongstrong covalent bonds covalent bonds

Carbon (ground state)

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


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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 Ability to form four strongstrong 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

• Catenation:

Ability of atoms in forming stable bonds with itself, hence joining

up into chains or rings

Ability to Ability to CatenateCatenate


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C – C > Si – Si > Ge – Ge > Sn – SnBond strength as bond length


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C – C > N – N > O – O

Bond strength

as the number of lone pairs


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CnH2n+2 n = 1,2,3,…(no limit for n)

SinH2n+2 n = 1 to 6 only silanes

GenH2n+2 n = 1 to 3 only germanes

SnnH2n+2 Only SnH4 (stannane) exists


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Carbon (excited state)


Ability to Form Multiple Ability to Form Multiple BondsBonds

sp2 bonds, 2 bonds

sp2

1 bond, 3 bonds

sp3

4 bonds


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Single bond Double bond Triple bond


* X = halogens


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Example 21-2Example 21-2 Check Point 21-2Check Point 21-2


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21.21.33Classification Classification

of Organic of Organic CompoundsCompounds


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• Organic compounds are classified by the the presence of characteristic functional groups.

21.3 Classification of Organic Compounds (SB p.7)

Functional Functional GroupsGroups


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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.




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• 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




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Homologous SeriesHomologous Series


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.

CH4 C2H6 C3H8 C4H10

CH2 CH2 CH2


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Number of carbon atom(s)

IUPAC name

Molecular formula

Condensed structural formula

Structural formula

1 Methane CH4 CH4

2 Ethane C2H6 CH3CH3

3 Propane C3H8 CH3CH2CH3

4 Butane C4H10 CH3CH2CH2CH3

The first four members of straight-chain alkanes


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Number of carbon atom(s)

IUPAC name

Molecular formula

Condensed structural formula

Structural formula

1 Methanol CH3OH CH3OH

2 Ethanol C2H5OH CH3CH2OH

3 Propan-1-ol

C3H7OH CH3CH2CH2OH

4 Butan-1-ol

C4H9OH CH3CH2CH2CH2OH

The first four members of straight-chain alcohols


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

e.g. alkanes: CnH2n+2

alkenes: CnH2n

alkynes: CnH2n-2




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



e.g. alkanols: CnH2n+1OH

alkanals: CnH2n+1CHO

alkanoic acids: CnH2n+1COOH


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Functional group of an

organic compound

Chemical properties

Members of a homologous series have similar chemical

properties




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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




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Number of

carbon atom(s)

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

–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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Number of

carbon atom(s)

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



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Example 21-3AExample 21-3A Example 21-3BExample 21-3B

Example 21-3CExample 21-3C Check Point 21-3Check Point 21-3


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21.21.44Factors Affecting Factors Affecting the Physical the Physical Properties of Properties of

Organic Organic CompoundsCompounds

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)

21.4 Factors Affecting the Physical Properties of Organic Compounds (SB p.17)

Main Factors Affecting the Main Factors Affecting the Physical Properties of Physical Properties of Organic CompoundsOrganic 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 Structure of Functional GroupGroup


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Structure of Functional Structure of Functional GroupGroup

Molecule Relative molecular

mass

Boiling point (oC)

Molecules with polar functional

groups

CH3CH2CH2OH 60 97.2

CH3CH2CH2NH2 59 48.6

CH3CH2Cl 64.5 12.5

CH3CH2COOH 60 141

Molecules with non-

polar functional

groups

CH3CH2CH2CH3 58 -0.5

CH3CH2CH=CH2 56 -6.2

CH3CH2CCH 54 8.1


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Dipole Moment of MoleculeDipole 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 Examples of Polar Molecules with Net Dipole Momentwith Net Dipole Moment


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Examples of Non-polar Examples of Non-polar Molecules with No Net Dipole Molecules with No Net Dipole MomentMoment


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Solubility of Organic Solubility of Organic MoleculesMolecules

• 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 Solubility of Organic MoleculesMolecules

Hexane in tetrachloromethane

Hexane in water


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Why does Hexane Dissolve Readily Why does Hexane Dissolve Readily in Tetrachloromethane?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 Why is Hexane Insoluble in Water?Water?


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Formation of Hydrogen Formation of Hydrogen BondingBonding• Molecules having OH or NH2

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 Why does Propan-1-ol have a Higher Boiling Point?a Higher Boiling Point?


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Formation of Hydrogen Formation of Hydrogen BondingBonding• 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 21-4AExample 21-4A

Example 21-4BExample 21-4B


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Length of Carbon Length of Carbon ChainsChains

• 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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Length of Carbon Length of Carbon ChainsChains• 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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Length of Carbon Length of Carbon ChainsChains• 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 21-4CExample 21-4C

Check Point 21-4Check Point 21-4


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FamilyGeneral formula

Functional group

Example

Formula IUPAC name

Alkane RH (Nil) CH3CH3 Ethane

Alkene

RCH = CH2

RCH = CHR

R2C = CHR

R2C = CR2

Carbon-carbon

double bond

CH2 = CH2 Ethene

AlkyneRC CH

RC CR

– C C –

Carbon-carbon triple

bond

HC CH Ethyne

Aromatic hydrocarbon

ArH

Phenyl group

Benzene


R = CnH2n+1 –


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Functional group

Example

Formula IUPAC name

Haloalkane RX X

halo groupCH3Cl Chloromethane

Alcohol ROH OH

hydroxyl groupCH3OH Methanol

Ether RO R O

oxy groupCH3 O CH3

Methoxymethane

Aldehyde

carbonyl group

Methanal

R = CnH2n+1 –



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Functional group

Example

Formula IUPAC name

Ketone

carbonyl group

Propanone

Carboxylic acid

carboxyl group

Ethanoic acid

Amine

RNH2

R2NHR3N amino group

CH3NH2 Methylamine

Nitrile RCN C N

nitrile groupCH3CN Ethanenitrile

R = CnH2n+1 –



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Functional group

Example

Formula IUPAC name

Ester

ester group

Methyl ethanoate

Acyl halide

acyl halide group

Ethanoyl chloride

Amide

amide group

Ethanamide

R = CnH2n+1 –



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Functional group

Example

Formula IUPAC name

Acid anhydride

acid anhydride group

Ethanoic anhydride

R = CnH2n+1 –



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The END


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(a)How was organic chemistry defined before 1800s? Answer

(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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(b) How is organic chemistry defined nowadays?

Back

Answer(b) Nowadays, scientists have discovered that

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

AnswerThe ability to catenate of carbon is chiefly due to

the high strength of the CC single bond (bond

enthalpy of C C single bond is 356 kJ mol-1).


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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 answer. Answer

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

Back

Answer

The electronic configuration of sulphur is 1s22s22p63s23p4. It

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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Identify the functional group(s) in the following compounds:

(a)

Answer(a) Carbon-carbon double bond ( ) and

chloro group (Cl)


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(b)

Answer(b) Carbonyl group ( )


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(c)

Answer(c) Amino group ( ) and carboxyl group

( )

Back


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To which homologous series does each of the following compounds belong?

(a)

Answer

(a) Ester


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(b)

Answer

(b) Amide


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(c)

Answer

(c) Acid anhydride

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 compounds that contain oxygen atoms in their functional groups. Answer(a) Alcohol, ether, aldehyde, ketone,

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

(b) OH (hydroxyl group)

and O (oxy group)


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

Answer

Back

(c) Br (bromo),

(aldehyde),

(acyl chloride),

(carbon-carbon

double bond) groups


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Why is oil immiscible with water?

AnswerOil molecules do not have free OH groups,

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?

AnswerGlucose molecules have OH groups, so

they are able to form hydrogen bonds with

water molecules. Therefore, glucose is

soluble in water despite it has a high

molecular mass. Back


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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 ethoxyethane are 117oC and 35oC respectively. Explain the difference. Answer


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There is an OH group in butan-1-ol. Thus, butan-1-ol molecules are

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.

Back


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Explain why propan-1-ol is soluble in water but

1-chloropropane is insoluble in water.

AnswerThe OH group of propan-1-ol molecules enables it to form

hydrogen bonds with water molecules. Thus it is soluble in water.

Although 1-chloropropane is a polar molecule, it does not form

hydrogen bonds with water molecules. So it is insoluble in water.

Back


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Which molecule would have a higher boiling point, 1-bromobutane or 2-bromobutane? Why?

Answer1-bromobutane would have a higher boiling point.

1-bromobutane is a straight-chain molecule while

2-bromobutane is a branched-chain molecule. Straight-chain

molecules have a greater surface area in contact with each

other, so greater intermolecular forces exist among the

molecules. Higher energy is required to break down the

intermolecular forces among the molecules of 1-bromobutane.

Back


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1-Chlorobutane and 2-chloro-2-methylpropane have the same molecular mass, yet their melting points differ. The melting point of 1-chlorobutane is –123oC while that of 2-chloro-2-methylpropane is –27.1oC. Explain the difference.

Answer


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Melting point is a measure of how efficient the molecules are packed

together in the solid state instead of just comparing the van der

Waals’ forces among molecules. Hence melting point is a function of

the efficient packing of molecules but not the contact surface area.

1-Chlorobutane is a straight-chain molecule while

2-chloro-2-methylpropane is a branched-chain molecule. As

2-chloro-2-methylpropane is more spherical and symmetrical, its

molecules are packed more efficiently in the solid state.

1-Chlorobutane is linear in shape and flattened, its packing in the

solid state is not so efficient. Hence, it has a lower melting point than

2-chloro-2-methylpropane.

Back


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(a) What are the major factors that affect the physical properties of organic compounds?

Answer(a) The physical properties of organic compounds

are mainly affected by the structure of the

functional groups, dipole moment of the

molecule, the formation of hydrogen bonding

between molecules, and the length of carbon

chains of the molecule.


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(b) The melting point and boiling point of pentane are –130oC and 36.3oC respectively while the melting point and boiling point of 2,2-dimethylpropane are –15.9oC and 9.5oC respectively. Account for the difference in melting point and boiling point between the two isomers.

Answer


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(b) Pentane is a straight-chain molecule, while 2,2-dimethylpropane

is a branched-chain molecule. Straight-chain molecules have a

greater surface area in contact with each other than branched-

chain molecules. Straight-chain molecules are held together by

stronger intermolecular forces. Therefore, pentane has a higher

boiling point than 2,2-dimethylpropane. Molecules of 2,2-

dimethylpropane are more spherical in shape and are packed

more efficiently in the solid state. Molecules of pentane are linear

in shape and flattened, so their packing in the solid state is not

efficient. Since extra energy is required to break down the efficient

packing of 2,2-dimethylpropane, 2,2-dimethylpropane has a

higher melting point than pentane.


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(c) Which molecule, hexane or cyclohexane, would have a higher melting point? Explain your answer.

Answer


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(c) Cyclohexane has a higher melting point than hexane. Molecules

of cyclohexane are more spherical in shape and are packed more

eff iciently in the solid state. Molecules of hexane are linear in

shape and flattened, so their packing in the solid state is not

efficient. Since extra energy is required to break down the efficient

packing of cyclohexane, cyclohexane has a higher melting point

than hexane.


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(d) Arrange the following molecules in increasing order of boiling points. Explain your answer.

Answer


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(d) The boiling points increase in the order:

butane < propanal < propan-1-ol

Molecules of butane are non-polar. Their molecules are held

together by weak instantaneous dipole-induced dipole

interactions. A relatively small amount of energy is required to

separate the molecules in the process of boiling. Both propanal

and propan-1-ol are polar molecules. Molecules of propanal are

held together by relatively weak dipole-dipole interactions, while

molecules of propan-1-ol are held together by intermolecular

hydrogen bonds. Since the intermolecular forces present in

molecules of propan-1-ol are stronger than those present in

molecules of propanal, a larger amount of energy is required to

separate the propan-1-ol molecules in the process of boiling.

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new way chemistry for hong kong a-level book 3a1 1 introduction to organic chemistry 21.1what is...

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