Topic 15 Hydrocarbons

Focus On STPM (Chapter 14, 15,16, 17)

14.2 General, empirical, molecular and structural formulae of organic compounds

(a) state general, empirical, molecular and structural formulae of organic compounds;

(b) determine empirical and molecular formulae of organic compounds.

14.3 Functional groups: classification and nomenclature

Structural formula –> IUPAC Name

IUPAC Name –> Structural formula

14.4 Isomerism: structural and stereoisomerism

(a) define structural and stereoisomerism (geometrical and optical);

(b) explain the meaning of a chiral centre in optical isomerism;

(c) classify isomers as structural, cis-trans and optical isomers;

(d) identify chiral centres and/ or cis-trans isomerism in a molecule of given structural formula;

(e) deduce the possible isomers for an organic compound of known molecular formula.

14.5 Free radicals, nucleophiles and electrophiles

(a) describe homolytic and heterolytic fissions;

(b) define the terms free radical, nucleophile and electrophile;

(c) explain that nucleophiles such as OH, NH3, H2O, Br, I and carbanion are Lewis bases;

(d) explain that electrophiles such as H+, NO2+, Br2, AlCl3, ZnCl2, FeBr3, BF3 and carbonium ion are Lewis acids.

14.6 Molecular structure and its effect on physical properties

(a) describe the relationship between the size of molecules in the homologous series and the melting and boiling points;

(b) explain the forces of attraction between molecules (van der Waals forces and hydrogen bonding).

14.7 Inductive and resonance effect

(a) explain inductive effect which can determine the properties and reactions of functional groups;

(b) use inductive effect to explain why functional groups such as NO2, CN, COOH, COOR, >C=O, SO3H, X (halogen), OH, OR, NH2, C6H5 are electron acceptors whereas R(alkyl) is an electron donor;

(c) explain how the concept of induction can account for the differences in acidity between CH3COOH, ClCH2COOH, Cl2CHCOOH and Cl3CCOOH; between ClCH2CH2CH2COOH and CH3CH2CHClCOOH;

(d) use the concept of resonance to explain the differences in acidity between CH3CH2OH and C6H5OH, as well as the differences in basicity between CH3NH2 and C6H5NH2.

15.1 Can understand and describe the alkanes

(c) describe the structural isomerism in aliphatic alkanes and cis-trans isomerism in cycloalkanes;

(d) state the physical properties of alkanes;

(g) explain the inertness of alkanes towards polar reagents;

(h) describe the mechanism of free radical substitution as exemplified by the chlorination of methane (with particular reference to the initiation, propagation and termination reactions);

(i) describe the oxidation of alkane with limited and excess oxygen, and the use of alkanes as fuels;

(j) explain the use of crude oil as a source of aliphatic hydrocarbons;

(k) explain how cracking reactions can be used to obtain alkanes and alkenes of lower Mr from larger hydrocarbon molecules;

15.2 Can understand and describe the alkenes

(c) describe structural and cis-trans isomerism in alkenes;

(d) state the physical properties of alkenes;

(e) define alkenes as unsaturated aliphatic hydrocarbons with one or more double bonds;

(f) describe the chemical reactions of alkenes as exemplified by the following reactions of ethene:

(i) addition of hydrogen, steam, hydrogen halides, halogens, bromine water and concentrated sulphuric acid,

(ii) oxidation using KMnO4, O2/Ag,

(iii) ozonolysis,

(iv) polymerisation;

(g) describe the mechanism of electrophilic addition in alkenes with reference to Markovnikov’s rule;

(h) explain the use of bromination reaction and decolourisation of MnO4 ions as simple tests for alkenes and unsaturated compounds;

(i) explain briefly the importance of ethene as a source for the preparation of chloroethane, epoxyethane, ethane-1,2-diol and poly(ethane).

15.3 Can understand and describe the arenes

(a) name aromatic compounds derived from benzene according to the IUPAC nomenclature, including the use of ortho, meta and para or the numbering of substituted groups to the benzene ring;

(b) describe structural isomerism in arenes;

(c) describe the chemical reactions of arenes as exemplified by substitution reactions of haloalkanes and acyl chloride (Friedel-Crafts reaction), halogen, conc. HNO3/conc. H2SO4 and SO3 with benzene and methylbenzene (toluene);

(d) describe the mechanism of electrophilic substitution in arenes as exemplified by the nitration of benzene;

(e) explain why benzene is more stable than aliphatic alkenes towards oxidation;

(f) describe the reaction between alkylbenzene and hot acidified KMnO4;

(h) explain the inductive effect and resonance effect of substituted groups (OH, Cl, CH3, NO2, COCH3, NH2) attached to the benzene ring towards further substitutions;

(i) predict the products in an electrophilic substitution reaction when the substituted group in benzene is electron accepting or electron donating;

16.1 Can understand and describe the haloalkanes

(c) describe the structural and optical isomerism in haloalkanes;

(e) describe the substitution reactions of haloalkanes as exemplified by the following reactions of bromoethane: hydrolysis, the formation of nitriles and the formation of primary amines;

(f) describe the elimination reactions of haloalkanes;

(g) describe the mechanism of nucleophilic substitution in haloalkanes (SN1 and SN2);

17.1 Introduction to hydroxy compounds

(c) describe structural and optical isomerism in hydroxy compounds;

17.2 Alcohols

(b) classify the reactions of alcohols whereby the ROH bond is broken: the formation of an alkoxide with sodium, esterification, acylation, oxidation to carbonyl compounds and carboxylic acids;

(c) classify the reactions of alcohols whereby the ROH is broken and OH is replaced by other groups: the formation of haloalkanes and the dehydration to alkenes and ethers;

17.3 Phenols

(b) describe the reactions of phenol with sodium hydroxide, sodium, acyl chlorides and electrophilic substitution in the benzene ring;

 

 

 

 

 

 

 

 

 

==============================================================

18 Carbonyl Compounds

(c) describe structural and optical isomerism in carbonyl compounds;

19 Carboxylic Acids and their Derivatives

19.1 Carboxylic acid

(c) describe structural and optical isomerism in carboxylic acids;

19.2 Acyl chlorides

(c) describe structural and optical isomerism in acyl chlorides;

19.3 Esters

(c) describe structural and optical isomerism in esters;

 

Summary of this chapter.

1. Hydrocarbons are compounds that contain the elements carbon and hydrogen only.
2. Alkanes are saturated hydrocarbons that contain only carbon-carbon single covalent bonds. Alkenes are unsaturated hydrocarbons that contain one or more carbon-carbon double bonds, C—C. Arenes are aromatic hydrocarbons that contain a benzene ring with six delocalised pi electrons.
3. The general formula of straight chain alkanes is CnH2n+2.
The general formula of straight chain alkenes is CnH2n.
4. All hydrocarbons have the following physical properties:
(a) Low boiling points due to the weak van der Waals forces between molecules. Boiling point increases as the relative molecular mass increases.
(b) Insoluble in water, soluble in organic solvents.
(c) Non-conductor of electricity.
5. All hydrocarbons undergo complete combustion to produce carbon dioxide and water, releasing heat. Lower members of alkanes are good fuels.
6. Alkanes undergo free radical substitution whereby the hydrogen atoms can be substituted by halogens such as chlorine and bromine in the presence of sunlight or ultraviolet light. The mechanism involves three steps: Initiation, propagation and termination.
7. Big molecules of alkanes are broken to smaller molecules by thermal cracking or catalytic cracking.
8. Alkenes undergo addition reaction in which a molecule is added across the double bond to form two single bonds, converting an unsaturated compound into a saturated compound.
9 Addition reactions of alkenes involve electrophilic addition which consists of two steps:
(a) An electrophile attacks the C=C bond to form a carbocation.
(b) A nucleophile attacks the carbocation to form a saturated compound.
10 Types of electrophilic addition on alkenes:
(a) Hydrogenation (with nickel or platinum as catalyst) to form alkanes.
(b) Halogenation (with bromine or chlorine) to form dihaloalkanes.
(c) Addition of hydrogen halide to form haloalkanes.
(d) Hydration (with concentrated H2SO, as catalyst) to form alcohol.
11. Alkenes undergo oxidation with:
(a) O2 in the presence of Ag as catalyst to form epoxyalkanes.
(b) cold acidified or alkaline KMnO4 to form diols.
(c) hot acidified KMnO4 to form two carbonyl compounds (cleavage of C = C bond).
(d) ozone, O3 to form ozonide, which can be reduced to produce carbonyl compounds.
12. The addition of HX to unsymmetrical alkene follows Markovnikov’s rule; in which the H atom is added to the carbon (of the double bond) containing the larger number of hydrogen atoms.
13. Alkenes undergo addition polymerisation to form addition polymers.
14. Benzene and arenes undergo electrophilic substitutions in which the hydrogen atoms in the benzene ring can be substituted. The mechanism consists of three steps:
(a) Formation of an electrophile.
(b) Electrophile attack on the n electrons in the benzene ring to form a carbocation.
(c) Carbocation loses a proton (H+) to restore the resonance in the benzene ring in the substituted product.
15. Types of electrophilic substitutions on benzene and alkylbenzene:
(a) Nitration: H substituted by -NO2 group using concentrated HNO3 and concentrated
H2SO4.
(b) Halogenation: H substituted by -Cl or -Br using halogen with halogen carrier catalyst.
(c) Friedel-Crafts alkylation: H substituted by -R using RCI and catalyst AICI3.
(d) Friedel-Crafts acylation: H substituted by -COR using RCOCI and catalyst AICI3.
(e) Sulphonation: H substituted by -SO3H using concentrated H2SO4.
16. Methylbenzene and alkylbenzene undergo three types of reactions:
(a) Alkyl side branch undergoes free radical substitution with halogen in the presence of uv light.
(b) Alkyl side branch undergoes oxidation to form benzoic acid with hot acidified KMnO4.
(c) Benzene ring undergoes electrophilic substitution.
17. Influence of a substituent group on the benzene on further substitution:
(a) Ring activating groups are ortho- and para-directing, examples: -OH, -NH2, -CH3
(except -Cl and -Br are deactivating but are ortho- and para-directing).
(b) Ring deactivating groups are meta-directing, examples: -NO2, -COOH, -CHO, -COCH3.
18. Benzene is a carcinogen that may cause the development of cancer cells.

 

….

1. Write the IUPAC names of the following alkenes.
a) CH3C(CH3)2-CH=CH2
b) CH3-CH=C(CH3)-CH=CH2
c) CH3CH=CHCH3.

2. Why alkene more smoky and luminous flame compared to the corresponding alkane with the same members of carbons?

3. Write the chemical equation and show the structural formula of the major product formed when 2-methylpropene reacts with hydrogen bromide. Name the mechanism of this reaction. Write equations to show the steps involved in this reaction mechanism.

4. Explain bromination test on alkene?

5. Explain the uses of halogenation to produce PVC?

6. Explain the reactivity of HX with alkenes? Arrange by increasing reactivity and give the reasons? HCl, HBr, HI?

7. Explain Markovnikov’s rule? What is major products?

8. Explain the major product of: hydrohalogenation and hydration.

9. Write equations to show the formation of the major organic compounds for the following reactions:
a) Hydration of 2,3-dimethylbut-1-ene,
b) Hydrogenation of 3-methylcyclohexene,
c) Oxidation of propene with oxygen in the presence of silver as a catalyst,
d) Oxidation of propene with ozone followed by reaction with zinc.

10. Explain oxidation of alkenes in reactiin between cold/ hot/ reflux with acidified/ alkaline KMnO4?

11. Predict the products formed when 3-methylbut-1-ene is
a) added with acidified potassium manganate(VIl)solution at room temperature,
b) added with bromine dissolved in tetrachloromethane,
c) refluxed with acidified potassium manganate(VIl)solution,
State the observation that will be noted in each case.

12. Write the equation for the reaction between 2-methylpropene with
a) cold acidified KMnO4 solution,
b) hot acidified KMnO4 solution?

13. A hydrocarbon with the molecular formula C4H8 forms a compound C3H6O2 after refluxing with acidified KMnO4. What is the structural formula of the hydrocarbon?

 

 

 

 

 

 

 

 

 

 

 

ALKENES

What is physical properties of alkenes?

How to naming alkene? Name the following alkene regarding to IUPAC name.
CH3C(CH3)2CH=CH2.
CH3CCH3=CHCH=CH2.

Draw the structure of the following alkenes?
3-methylcyclohexene,
2,3-dimethylcyclohexene,
ethylene,
propylene, isobutylene.

How cis-trans isomers in alkenes formed?

What types of isomers of cis-trans isomers?

What is the properties of two cis-trans isomers?

Sketch the C4H8 of the three structural isomers?

What happens when the number of carbon atoms in the molecules increases?

What is chemical properties of alkenes?

There are two reactions alkene undergo?
1. electrophilic addition,
2. oxidation.

15 Hydrocarbons

15.1 Can understand and describe the alkanes

 

15.2 Can understand and describe the alkenes

What is the product of reactions 2-pentene with hydrogen bromide?

2-bromopentane (has chiral carbon which is optically active compound, isomer differ in the arrangement if atoms in 3D space which create miror images of each other) and 3-bromopentane.

15.3 Can understand and describe the arenes

15 Hydrocarbons

15.1 Can understand and describe the alkanes

Candidates should be able to:

(a) write the general formula for alkanes;

(b) explain the construction of the alkane series (straight and branched), and IUPAC nomenclature of alkanes for C1 to C10;

(c) describe the structural isomerism in aliphatic alkanes and cis-trans isomerism in cycloalkanes;

(d) state the physical properties of alkanes;

(e) define alkanes as saturated aliphatic hydrocarbons;

(f) name alkyl groups derived from alkanes and identify primary, secondary, tertiary and quartenary carbons;

(g) explain the inertness of alkanes towards polar reagents;

(h) describe the mechanism of free radical substitution as exemplified by the chlorination of methane (with particular reference to the initiation, propagation and termination reactions);

(i) describe the oxidation of alkane with limited and excess oxygen, and the use of alkanes as fuels;

(j) explain the use of crude oil as a source of aliphatic hydrocarbons;

(k) explain how cracking reactions can be used to obtain alkanes and alkenes of lower Mr from larger hydrocarbon molecules;

(l) discuss the role of catalytic converters in minimising air pollution by oxidising CO to CO2 and reducing NOx to N2;

(m) explain how chemical pollutants from the combustion of hydrocarbon affect air quality and rainwater as exemplified by acid rain, photochemical smog and greenhouse effect.

15.2 Can understand and describe the alkenes

Candidates should be able to:

(a) write the general formula for alkenes;

(b) name alkenes according to the IUPAC nomenclature and their common names for C1 to C5;

(c) describe structural and cis-trans isomerism in alkenes;

(d) state the physical properties of alkenes;

(e) define alkenes as unsaturated aliphatic hydrocarbons with one or more double bonds;

(f) describe the chemical reactions of alkenes as exemplified by the following reactions of ethene:

(i) addition of hydrogen, steam, hydrogen halides, halogens, bromine water and concentrated sulphuric acid,

(ii) oxidation using KMnO4, O2/Ag,

(iii) ozonolysis,

(iv) polymerisation;

(g) describe the mechanism of electrophilic addition in alkenes with reference to Markovnikov‟s rule;

(h) explain the use of bromination reaction and decolourisation of MnO4 ions as simple tests for alkenes and unsaturated compounds;

(i) explain briefly the importance of ethene as a source for the preparation of chloroethane, epoxyethane, ethane-1,2-diol and poly(ethane).

15.3 Can understand and describe the arenes

Candidates should be able to:

(a) name aromatic compounds derived from benzene according to the IUPAC nomenclature, including the use of ortho, meta and para or the numbering of substituted groups to the benzene ring;

(b) describe structural isomerism in arenes;

(c) describe the chemical reactions of arenes as exemplified by substitution reactions of haloalkanes and acyl chloride (Friedel-Crafts reaction), halogen, conc. HNO3/conc. H2SO4 and SO3 with benzene and methylbenzene (toluene);

(d) describe the mechanism of electrophilic substitution in arenes as exemplified by the nitration of benzene;

(e) explain why benzene is more stable than aliphatic alkenes towards oxidation;

(f) describe the reaction between alkylbenzene and hot acidified KMnO4;

(g) determine the products of halogenation of methylbenzene (toluene) in the presence of

(i) Lewis acid catalysts,

(ii) light;

(h) explain the inductive effect and resonance effect of substituted groups (OH, Cl, CH3, NO2, COCH3, NH2) attached to the benzene ring towards further substitutions;

(i) predict the products in an electrophilic substitution reaction when the substituted group in benzene is electron accepting or electron donating;

(j) explain the uses of arenes as solvents;

(k) recognise arenes as carcinogen.

15 Hydrocarbons

15.1 Can understand and describe the alkanes

Candidates should be able to:

(a) write the general formula for alkanes;


(b) explain the construction of the alkane series (straight and branched), and IUPAC nomenclature of alkanes for C1 to C10;

branched / IUPAC nomenclature of alkane

 

 

 

straight / IUPAC nomenclature of alkane

cyclo / ring

 

(c) describe the structural isomerism in aliphatic alkanes and cis-trans isomerism in cycloalkanes;

structural isomerism in aliphatic alkanes kiv
cis-trans isomerism in cycloalkanes

 

(d) state the physical properties of alkanes; (Go to van der Waals forces)

 

(e) define alkanes as saturated aliphatic hydrocarbons;

(f) name alkyl groups derived from alkanes and identify primary, secondary, tertiary and quartenary carbons;

name alkyl groups (common names)

primary, secondary, tertiary and quartenary

(g) explain the inertness of alkanes towards polar reagents;

(h) describe the mechanism of free radical substitution as exemplified by the chlorination of methane (with particular reference to the initiation, propagation and termination reactions);

mechanism of free radical substitution (chlorination of methane)

 

 

chlorination vs bromination

(i) describe the oxidation of alkane with limited and excess oxygen,

and the use of alkanes as fuels;

(j) explain the use of crude oil as a source of aliphatic hydrocarbons;

kiv

(k) explain how cracking reactions can be used to obtain alkanes and alkenes of lower Mr from larger hydrocarbon molecules;

 

 

 

(l) discuss the role of catalytic converters in minimizing air pollution by oxidizing CO to CO2 and reducing NOx to N2;

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(m) explain how chemical pollutants from the combustion of hydrocarbon affect air quality and rainwater as exemplified by acid rain, photochemical smog and greenhouse effect.

chemical pollutants

 

 

 


combustion of hydrocarbon (do fire contains plasma?)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

air quality and

 

 

 

 

 


rainwater (harvesting)

 

 

 

 

 

 

 


acid rain


photochemical smog

 

 

 

 

 

 

 

 

 

 

 


greenhouse effect.

 

15.2 Can understand and describe the alkenes

 

 

 

Candidates should be able to:

(a) write the general formula for alkenes;

(b) name alkenes according to the IUPAC nomenclature and their common names for C1 to C5;

 

 

(c) describe structural and cis-trans isomerism in alkenes;

(d) state the physical properties of alkenes;

(e) define alkenes as unsaturated aliphatic hydrocarbons with one or more double bonds;

 

(f) describe the chemical reactions of alkenes as exemplified by the following reactions of ethene:

(i) addition of hydrogen, steam,


hydrogen halides,

 

 

 

halogens,

 


bromine water and

 

 

 

concentrated sulphuric acid,

 

(ii) oxidation using KMnO4,

if hot acidified first will produce diol (intermediate) then ckeavage into carbonyl (ketone and carboxylic acid)

 

O2/Ag,



(iii) ozonolysis,

 


(iv) polymerisation;

 

 

(g) describe the mechanism of electrophilic addition in alkenes with reference to Markovnikov’s rule;

 

 

 

(h) explain the use of bromination reaction and decolourisation of MnO4 ions as simple tests for alkenes and unsaturated compounds;

 

 

 

 

 


(i) explain briefly the importance of ethene as a source for the preparation of chloroethane, epoxyethane, ethane-1,2-diol and poly(ethane).

 

 

 

15.3 Can understand and describe the arenes

 

 

 

 

 

 

Candidates should be able to:

(a) name aromatic compounds derived from benzene according to the IUPAC nomenclature, including the use of ortho, meta and para or the numbering of substituted groups to the benzene ring;

 

 

 

 

(b) describe structural isomerism in arenes;


(c) describe the chemical reactions of arenes as exemplified by substitution reactions of haloalkanes and acyl chloride (Friedel-Crafts reaction), halogen, conc. HNO3/conc. H2SO4 and SO3 with benzene and methylbenzene (toluene);

 

 

 

 

 

 

 

 

 

 

(d) describe the mechanism of electrophilic substitution in arenes as exemplified by the nitration of benzene;

 

 

 

(e) explain why benzene is more stable than aliphatic alkenes towards oxidation;

 

 

 

(f) describe the reaction between alkylbenzene and hot acidified KMnO4;

 

(h) describe the mechanism of free radical substitution as exemplified by the

 

 

 

(g) determine the products of halogenation of methylbenzene (toluene) in the presence of

(i) Lewis acid catalysts,

 

 

 

 


Akylation of Benzene by using Friedel Craft reagent:


(ii) light;

 

(h) explain the inductive effect and resonance effect of substituted groups (OH, Cl, CH3, NO2, COCH3, NH2) attached to the benzene ring towards further substitutions;

OH, Cl, CH3, NO2, COCH3, NH2

OH

Cl

CH3
NO2,
COCH3
NH2

 

 

 

 

 

 

 

(i) predict the products in an electrophilic substitution reaction when the substituted group in benzene is electron accepting or electron donating;


(j) explain the uses of arenes as solvents;

 

(k) recognise arenes as carcinogen.

other links for online notes





Add Comment