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Perpustakaan
Careen, Ess
Hoo Jing Ying. isB
1. Chemistry, Organic.
2. Chemistry.
i t
iii. 547
Designed by Rachel Goh typeset by Helen Wong
Printed by Vinlin Press sdn Bhd, selangor
Cover image: sUWit nGaOKaEW/shutterstock.com image used under licence from shutterstock.com
“Chlorine is a deadly poison gas employed on European battlefields in World War I. Sodium is a corrosive metal which burns upon contact with water. Together they make a placid and unpoisonous material, table salt. Why each of these substances has the properties it does is a subject called chemistry.”
Carl Sagan
Chemistry is an endlessly fascinating, if challenging, subject. Essential Organic Chemistry aims to prepare students for the Cambridge International AS and A Level Chemistry (9701) examinations. It is a culmination of the teaching experiences of Sunway College A-Level lecturers Careen Teh, Tan Ai Nee, and Hoo Jing Ying. Sunway College’s A-Level programme has consistently been recognised and awarded for being among the best in Malaysia and the world; the invaluable efforts of our lecturers have been instrumental in contributing to our students’ lofty achievements, and their excellence is replicated in this book.
I believe the insights provided in this book make it a highly effective learning tool that will help students understand the subject in preparation for their A-Level examinations.
Professor Dato’ Elizabeth Lee Chief Executive Officer Sunway Education GroupThis book is tailored for students undertaking the Cambridge International AS and A Level Chemistry (9701) examinations and covers topics for the latest syllabus.
Key features of the book:
Concise Explanations
Each chapter has brief but comprehensive explanations on key points and topics.
Hint!
this box contains tips to improve understanding of basic Chemistry concepts.
molecules are more soluble in water than non-polar molecules. For
46) is soluble in water, propane,
smaller alcohol and carboxylic acid molecules are soluble in water as they can form hydrogen bonds with water molecules. Solubility
Illustrative Figures
this book contains figures to illustrate essential concepts.
Breaking of Covalent Bond
1 When organic reactions occur, covalent bonds in the reactant molecules are broken. The breaking of a covalent bond is called bond fission
2 A covalent bond is formed by the sharing of two electrons from two atoms. During bond fission, the two shared electrons are redistributed. This can happen in two ways:
fission
Homolytic Fission
1 Homolytic fission occurs when a bond splits evenly with one electron from the covalent bond going to each atom.
2 Homolytic fissions occur in the presence of ultraviolet light or at high temperatures.
Examiner’s Tip this box contains advice from Cambridge examiners on how to score high marks.
(b) It acts as the catalyst, as it is regenerated.
6 Glyoxal, a two-carbon compound, is subjected to two successive reactions to produce tartaric acid, a four-carbon compound.
OHCCHO Reaction 1 intermediate Reaction 2 HOOCCH(OH)CH(OH)COOH
Past-Year Questions
these are actual past examination questions that can be used for your own practice and assessment.
delocalised into the benzene ring/lone pairs of electrons on nitrogen overlaps with the pi ring system. – Hence, the lone pair of electrons is less available to form dative covalent bonds with H+ ions.
Formation of Aliphatic Amine
2 Propylamine can be synthesised from bromoethane by the following route.
CH3CH2Br X Step 1 Step 2 CH3CH2CH2NH2
(a) Draw the structure of the intermediate compound X in the box above. (b)
Examiner’s Corner this section is a guide on answering multiplechoice and past-year questions with advice from Cambridge examiners.
Guided Answers these are detailed explanations of how to answer questions correctly. For multiplechoice questions, they also explain why the others answers are incorrect.
1 Organic Chemistry is the study of carbon compounds in which hydrogen is almost always present. Organic compounds that consist of carbon and hydrogen only are called hydrocarbons.
2 Carbon forms millions of different organic compounds. This is due to the ability of carbon to form stable chains and rings of carbon atoms.
3 Organic compounds can be divided into two main groups, namely aliphatic compounds and aromatic compounds.
(a) Aliphatic compounds carbon compounds, or cyclic compounds which contain closed rings of carbon atoms. Each carbon uses all its four outer-shell electrons for bonding.
CH3CH2CH2CH
Straight chain
(b) Aromatic compounds molecule. A benzene molecule is a six-carbon ring and each carbon is bonded to one hydrogen. The carbon in a benzene ring uses three outer-shell electrons for bonding. The formula of benzene is C6H6 which is represented as a hexagon with a circle in it.
Delocalised electrons
Benzene ring
Delocalised electrons are nonbonding electrons that are not associated with a single atom. They occur as electron clouds spread over more than one atom.
1 A homologous series is a family of organic compounds with the same functional group, arranged in ascending order of molecular size.
2 A functional group is the part of the molecule or a group of atoms that is attached to the main hydrocarbon chain that is responsible for the chemical and physical properties of the compound. It is the part of the molecule that changes after a chemical reaction.
3 Generally, organic compounds in the same homologous series have similar chemical properties and show a gradual change in their physical CH2 — O — H
The functional group of an alcohol molecule is the hydroxy group, —OH Compounds of the same homologous series contain the same
The members of the same homologous series have the same general formula. Table 1.1 shows the first four members of the alkene
2n .
The first four members of the homologous series of alkenes
The names of some common homologous series and their functional groups are shown in Figure 1.4.
1 For consistency, the IUPAC (International Union of Pure and Applied Chemistry) nomenclature (naming system) is used to name organic compounds systematically.
2 In general, the name of an organic compound consists of three parts:
Name and location of branched Based on number of carbons in the Functional group of the compound
Prefix Root name Suffix + + is based on the number of carbon atoms in the longest continuous carbon chain in each molecule. This chain is
identifies the functional group present in the compound. It indicates the homologous series of the compound.
(c) The prefix shows the name of any branched group (or substituent) attached to the parent chain, as well as its location (given by a number assigned to the carbon atom it is attached to in the parent chain).
• The name of a hydrocarbon branch is based on the number of carbon atoms in the group (refer to Table 1.2) and ends in the letters -yl. For example, –CH3 is a methyl branch and –C2H5 is an ethyl branch.
• The location of each branch is designated by an appropriate (and smallest possible) number.
• If the branched group occurs more than once, the location of each group must be given. The number of times the group occurs is indicated by a prefix (
• If there are two or more listed in alphabetical order.
The name “2-methylpropane” indicates an alkane (suffix: –ane) with a three-carbon parent chain (root name: prop-), and a onecarbon branch (–CH
3 Note that we cannot attach a branch to the first or last carbon of the main carbon chain. If we do that, that carbon effectively becomes a part of the parent chain.
4 If the organic molecule contains carbons in a ring (cyclic compounds), its chemical name is designated by the prefix cyclo
5 Let us review the IUPAC rules for naming some common organic compounds and look at some examples.
Alkanes are a family of molecules containing carbon and hydrogen connected by single bonds only. These molecules can be continuous chains or rings.
1 To name the alkane, first identify and name the longest carbon chain (root name).
2 Then, append the letters ‘ane’ at the end of the name to denote an
Finally, name any branches and their locations (prefix). Alkanes do not contain a functional group and so the carbons of the parent chain are numbered from the end that gives the branched groups the lowest
These groups of molecules contain branched substituent groups and functional groups. The location of the functional group is indicated in the name of the compound.
1 Identify and name the longest carbon chain (root name).
2 Add the letters ‘-ene’ or ‘-ol’ at the end of the name to denote an alkene or an alcohol (suffix).
3 Assign a number to the functional group location, numbering the carbons of the parent chain from the end nearest the functional group.
4 Name the branches and indicate their locations (prefix).
Examples:
➊ Alkene (Functional group: C=C double bond)
1 2 3 4 (✔) Methyl branch (prefix)
CH2= CHCHCH3 | CH3
CH2= CHCHCH3 | CH3
4 3 2 1 (✘)
3-methylbut-1-ene
➋ Alcohol (Functional group: hydroxy group –OH)
CH3CHCH CH OH CH Methyl branch (prefix)
➌ Halogenoalkane (Functional group: C Cl | CH3— CH — CH 1 2 2-chlorobutane
➍ Ketone (Functional group: C
CH CHCH CH OH
CH3— C — CH — CH || | O CH
1 2 3 3-methylbutan-2-one
These groups of molecules contain branched substituent groups and functional groups, but the location of the functional group is not required in the name of the compound.
1 Identify and name the longest carbon chain (root name).
2 Append the letters ‘–oic acid’ or ‘- al’ to the name of the compound to denote a carboxylic acid or an aldehyde (suffix).
3 Name any branches and their locations (prefix). Note that the functional group is always appended to the end/terminal carbon and the functional group carbon location is designated as carbon 1. The location of the functional group is not required.
Halogenoalkanes and ketones are named similarly: For halogenoalkanes, the words ‘fluoro’, ‘chloro’, ‘bromo’ or ‘iodo’ are prefixed to the name of the parent alkane chain. Ketones are named by removing the ending ‘-e’ from the name of the parent alkane chain and replacing it with ‘-one’.
Examples:
➊ Carboxylic acid (Functional group: carboxyl group COOH)
➋
An ester molecule is formed from an alcohol and a carboxylic acid. The first part of its name is derived from the alcohol and the second part of the name
Different types of formula can be used to represent an organic molecule.
1 Empirical Formula
The empirical formula of a compound gives the simplest ratio of the number of atoms of each element present in one molecule of the compound.
2 Molecular Formula
The molecular formula shows the actual number of atoms of each element in the molecule and is an integral multiple of the empirical formula.
Examples:
• The molecular formula of ethene is C2H4 and its empirical formula is CH2.
C2H4 CH2
Molecular formula Empirical formula
• The molecular formula of glucose is C6H12O6 and its empirical formula is CH2O.
C6H12O6 CH2O
Molecular formula Empirical formula
3 Structural Formula
This gives the arrangement of atoms within the molecule. It shows the sequence or order in which the atoms are bonded to each other. A structural formula can be either condensed or displayed (full structural formula).
• A displayed/full structural formula arrangement of atoms relative to each other. All the covalent bonds present in the organic compound must be shown as lines between the atoms.
Examples: H H
H — C — C — C — O — H
Propanol
• A condensed structural formula carbon atom separately.
Examples:
CH3CH2CH2OH CH3CH2CN
Propanol Propanenitrile
4 Three-dimensional (3D) Formula
This attempts to show the three-dimensional shape of the molecule. The bonds are shown using these conventional symbols:
A bond in the plane of the paper is shown as a solid line.
A bond going back into the paper is indicated as a dashed line.
A bond coming out of the paper is shown as an enlarging wedge.
HINT!
Covalent compounds have bonds where electrons are shared between atoms. The covalent bonds are polar or non-polar depending on whether the atoms have similar or very different electronegativities.
5 Skeletal Formula
This is a simplified representation of an organic compound. It is derived from the structural formula by omitting the carbon atoms and the hydrogen atoms that are bonded to the carbon atoms. It shows the main carbon chain as a zig-zag line along with the functional group. A carbon atom is present at the start, at the end, and at every turn of the zig-zag
1 Organic molecules are simple covalent substances. So, they are usually gases, volatile liquids with low boiling points, or solids with low melting points.
2 The physical properties of organic molecules are determined by the polarity of their covalent bonds, and the size and shape of their molecules.
The melting and boiling points of an organic compound are dependent on the following trends.
Boiling point (and melting point) increases with the size of molecules. As molecular size increases, the strength of the instantaneous dipoleinduced dipole attraction between molecules becomes stronger, and more energy is required to overcome the stronger intermolecular attraction. For instance, the boiling point of methane (M r = 16) is –164 ºC while the boiling point of ethane (M r = 30) is –89 ºC.
The effect of branching is the lowering of the boiling point for molecules with similar molecular size. Branched molecules have less surface area and less contact points for intermolecular attractions to act on. This decreases the ability of individual molecules to attract each other and as a result, the boiling point decreases.
(a) Unbranched molecule
CH3 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH3
(b) Branched molecule
CH3 C CH3
Stronger temporary dipole-induced dipole attractions
Higher boiling point
Less surface area/ less contact points
Less temporary dipole-induced dipole forces
Lower boiling point
Polar molecules have higher boiling points than non-polar molecules of similar molecular size. The presence of stronger intermolecular attractions, namely permanent dipole-dipole attraction and the hydrogen bond, increases the boiling point.
Alcohols and carboxylic acids, in particular, have higher boiling points due to the stronger hydrogen bonds between their molecules. This is shown in Table 1.4.
1 Polar molecules are more soluble in water than non-polar molecules. For instance, while ethanol, C2H5OH (M r = 46) is soluble in water, propane, C3H8 (M r = 44), is not soluble in water.
2 The smaller alcohol and carboxylic acid molecules are soluble in water as they can form hydrogen bonds with water molecules. Solubility decreases when molecular size increases as the alkyl group which is nonpolar gets larger.
1 When organic reactions occur, covalent bonds in the reactant molecules are broken. The breaking of a covalent bond is called
2 A covalent bond is formed by the sharing of two electrons from two atoms. During bond fission, the two shared electrons are redistributed. This can happen in two ways:
• Homolytic fission
• Heterolytic fission
1 Homolytic fission occurs when a bond splits evenly with one electron from the covalent bond going to each atom.
2 Homolytic fissions occur in the presence of ultraviolet light or at high temperatures.
The bigger the body (alkyl group), the less significant the tail (OH group). Therefore, as molecular size increases, its ability to form hydrogen bonds with water molecules decreases.
The products of bond breaking are not stable. Such species are known as reactive intermediates. They are highly reactive and will quickly convert to a more stable molecule.
3 The intermediate species formed during homolytic fission are free radicals. A radical is an atom or a group of atoms with an unpaired electron and is very reactive and unstable.
4 To depict the movement of a single electron in a reaction, a half-arrow (fishhook) is used.
Examples:
Heterolytic fission occurs when both the shared electrons in a covalent
The intermediate species formed during heterolytic fission are positive is a carbon species that carries a
A full arrow is used to represent the movement of two electrons in a
1 Free radicals are classified as primary (1°), secondary (2°) or tertiary (3°) radicals.
2 The number of hydrogen or alkyl group bonded to the carbon with an unpaired electron determines the classification of a free radical. A primary free radical has two hydrogens and one alkyl group bonded to the carbon with an unpaired electron.
3 The greater the number of alkyl groups bonded to the carbon with an unpaired electron, the more stable the radical.
Relative stability: primary radical < secondary radical < tertiary radical
1 Carbocations are also classified as primary (1°), secondary (2°) or tertiary (3°) carbocations.
2 The positively-charged carbon is bonded to three other atoms or groups of atoms. The number of hydrogen or alkyl group bonded to the positively-charged carbon determines its classification:
(a) A primary carbocation has two hydrogens and one alkyl group bonded to the carbon that is positively charged.
(b) A secondary carbocation has one hydrogen and two alkyl groups bonded to the carbon that is positively charged.
(c) A tertiary carbocation has three alkyl groups bonded to the carbon that is positively charged.
3 The more alkyl groups that are bonded to the positively-charged carbon, the more stable is the carbocation. Alkyl groups are electron donating (positive inductive effect) which reduces the positive charge of the carbocation making it more stable.
1 Nucleophiles are reagents that contain a lone pair of electrons.
2 Nucleophiles are neutral molecules or anions (e.g. OH–, Cl–, NH3, CN–, Br–, R-NH2, H2O).
3 In chemical reactions, a nucleophile seeks a positive centre. It attacks a positively-charged carbon atom or an electron-deficient carbon in the molecule (shown by δ+ sign) of the organic reactant and donates an
Molecule with electron-deficient carbon
A nucleophile donates a pair of electrons to an electrophile to form a are reagents that accept electrons. They are electron-
They are attracted to regions of negative charge or electron-rich sites in C double bond and the benzene ring which , NO2+), carbocations or partially positively-charged regions of polar covalent bonds.
4 During a chemical reaction, they accept a pair of electrons from a nucleophile or an electron-rich particle.
1 Substitution Reaction
This is a reaction where an atom or group of atoms replaces an atom in the reactant molecule. Halogenation is a good example of a substitution reaction. When methane is reacted with chlorine, chloromethane and hydrogen chloride are produced.
2 Addition Reaction
In an addition reaction, two or more smaller molecules react to become one larger molecule. For example, when bromine is shaken with an alkene, the colour of bromine quickly disappears and the compound 1,2-dibromoethane is formed.
C2H4 + Br2 → C2H4Br2
3 Elimination Reaction
In an elimination reaction, an atom or a group of atoms is removed from a larger organic reactant. The product formed is normally an alkene which is unsaturated.
4 Hydrolysis
Hydrolysis is a reaction in which water is a reactant. The reaction is often catalysed by a dilute acid or alkali and requires heating. The hydrolysis of ethanenitrile under acidic conditions, for example, gives ethanoic acid.
CH3
5 Condensation Reaction
This is a reaction in which two molecules combine to form a larger molecule with the release of water or some other small molecule. An example is the condensation of two amino acids (glycine) to form a peptide.
NH2CH2CO2H + NH
6 Oxidation
This reaction occurs when a reactant molecule gains oxygen or loses hydrogen. In equations for organic redox reactions, the symbol [O] represents the oxygen atom from an oxidising agent and the symbol [H] represents the hydrogen atom from a reducing agent.
CH3CHO + [O] → CH3COOH
Ethanal, CH3CHO, is oxidised as it has gained an oxygen atom from the oxidising agent.
7 Reduction
This occurs when a reactant molecule loses oxygen or gains hydrogen.
CH3CN + 4[H] → CH3CH2— NH2
Ethanenitrile CH3CN is reduced as it has gained four hydrogen atoms from the reducing agent.
Isomers are compounds that have the same molecular formula but a different arrangement or orientation of atom(s) in space. There are two main types of isomers: structural isomers and stereoisomers.
same molecular formula but different . There are three types of structural isomers: chain isomers, positional isomers and functional group isomers.
Chain isomers have carbon chains of different length or have different numbers of branches. The carbon atoms may be arranged in one continuous chain, or the chain may have multiple groups of carbon branching off. These isomers generally have the same chemical properties but different physical properties. For example, branched isomers have lower boiling points than the unbranched isomer.
3 Positional Isomerism
Positional isomerism is due to the functional group occupying different positions in the same main carbon chain. H H H
H — C — C — C — H
Figure 1.14 In positional isomerism, the basic carbon skeleton remains unchanged while a functional group is moved to a different location
4 Functional Group Isomerism
Functional group isomers have different functional groups. As they belong to different homologous series, these isomers have different physical and chemical properties.
Ethanol
Boiling point = 78
Figure 1.15 Functional group isomers contain different functional groups
1 Stereoisomers have the same molecular and structural formulae but differ in spatial arrangement or orientation of the atoms. This refers to how the different atoms are oriented in the space around the carbon chain.
2 There are two types of stereoisomers: geometric or cis-trans isomers and optical isomers.
1 Cis-trans isomerism, also known as geometrical isomerism, arises in alkenes and involves the carbon-to-carbon double bond.
2 Each double-bonded carbon must be bonded to two different atoms or groups of atoms.
3 Cis-trans isomerism arises from the restricted rotation of the carbon-tocarbon double bond, compared to the single bond that can rotate freely. If the C=C bond is rotated, the pi bond will be broken. (A double bond is composed of one sigma and one pi bond.)
4 The cis isomer of 2,4-dichlorobut-2-ene has two identical atoms or groups of atoms on the same side of the double bond. The trans isomer has two identical atoms or groups of atoms on opposite sides of the double bond.
isomers have the same chemical properties but different
isomer generally has a higher boiling point due to the presence of a net dipole when polar covalent bonds are present. This gives rise to stronger intermolecular forces between the molecules. isomer has a higher melting point as its molecules are more
H C = C
H CH3
trans-but-2-ene
Non-polar molecule
Boiling point: 0.9 oC
Melting point: –138.9
Melting point: –105.5 oC
6 The maximum number of possible cis-trans isomers is given by the formula 2n, where n stands for the number of C=C double bonds in the alkene molecule that is able to exhibit cis-trans isomerism.
There are two C=C bonds present in the molecule. Therefore, the number of isomers = 22 = 4.
The four isomers:
1 Optical isomerism occurs when a carbon atom in a molecule has four different atoms or groups of atoms bonded to it. This carbon is called a chiral centre or
2 Optical isomers come in pairs where the two isomeric forms are mirror images of each other. The isomers have no plane of symmetry and cannot be superimposed on each other.
(a) Optical isomers of butan-2-ol
(b) Optical isomers of 2-aminopropanoic acid
3 Optical isomers are so named because of their effect on plane-polarised light (light restricted to a single plane). When plane-polarised light is passed through samples of the isomers, the plane of the polarised light is rotated in opposite directions. One optical isomer rotates polarised light clockwise and the other isomer rotates polarised light in an anticlockwise direction.
4 Molecules that can rotate polarised light are said to be optically active
5 Optical isomers are also called enantiomers. A mixture containing both enantiomers in equal concentrations or amounts is called a racemic mixture. This mixture is optically inactive because the rotating power of one enantiomer cancels that of the other.
Optical isomers have the same physical properties, such as the melting point, boiling point and solubility in a particular solvent.
Optical isomers basically have similar chemical properties except in reactions with other optically active reagents especially in biological
The number of optical isomers for a given molecule is given by the stands for the number of chiral centres in the
1 State the names of the following hydrocarbons:
(a) H CH3 H H
H — C — C — C — C — H
H H H H
(b)
H — C — C
H — C — H H H
H H — C — H
(c) H
H — C — H H
H — C — C
Answer:
(a) 2-methylbutane
(b) 2,3-dimethylbut-2-ene
(c) 2-methylprop-1-ene or 2-methylpropene
Names of Halogenoalkanes
2 State the names of the following halogenoalkanes:
(a) H H H H
H — C — C — C — C — H
(b) H H Br H H
H — C — C — C — C — C — H
Name of Compounds with Oxygen-Containing Functional Group
3 What are the names of the following compounds?
(a) H H H
HO — C — C — C — OH
OH H
(b)
(c)
Answer:
(a) propane-1,2,3-triol
(b) 2-methylpropanoic acid
(c) methyl methylpropenoate
Compounds with Two Different Functional Groups
4 What are the names of the following compounds?
Answer:
(a) 3-hydroxybutan-2-one
Explanation:
When a compound has two and more functional groups, the order of precedence determines which groups are named with the prefix or suffix forms. The order of precedence for some of the oxygencontaining functional groups are shown in Figure 1.19.
Order of precedence of oxygen-containing functional groups
The group that has higher precedence takes the suffix, with all others taking the prefix form. Based on the order of precedence of the functional groups, a ketone has a higher precedence over an alcohol. Hence, ketone is the suffix while alcohol is the prefix.
Explanation:
Based on the order of precedence of the functional groups, carboxylic acid has higher precedence over ketone. Hence, carboxylic acid is the suffix while ketone is the prefix. When a ketone exists in the form of a prefix, it is named -oxo