Organic Chemistry

(a) C₂H₄

(b) Electron dot formula of ethene:

(c) Structural formula of ethene:

(a) n is the number of carbon atoms in the molecule and 2n is the number of hydrogen atoms.

(b) Butene

(c) When n=4 then no. of carbon atoms is n=4 and hydrogen atoms is 2n=8, hence alkene is C₄H₈

(d) When 2n=10 then no. of carbon atoms is n=5 and hydrogen atoms is 2n=10, hence alkene is C₅H₁₀

(e) Third member of the alkene family is Butene. Its structural formula is shown below:

(f) Lower homologous: C₃H₆

Higher homologues : C₅H₁₀

Structural formula of Ethane [saturated]:

Structural formula of Ethene [unsaturated]:

Butene has three isomers:

But−1−ene — CH₃-CH₂-CH=CH₂

But−2−ene — CH₃-CH=CH-CH₃

2-methyl-prop-1-ene — CH₂=C(CH₃)-CH₃

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

The gas is collected by downward displacement of water.

(a) Dehydrohalogenation involves elimination of hydrogen halide.

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \underset{\text{ Potassium bromide}}{\text{KBr}} + \text{H}_2\text{O}$

The products formed are ethene, potassium bromide and water.

(b) Dehydration involves elimination of elements of water from alcohol. Conc. sulphuric acid act as dehydrating agent.

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

The products formed are ethene and water.

(a)

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}$

Product formed is 1,2, dichloroethane [ethylene chloride]

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}$

Product formed is 1,2, dibromooethane [ethylene bromide]

(b) Conditions for hydrogenation of ethene : finely divided catalyst, such as platinum or palladium at ordinary temperature or nickel at 200°C. Main product formed is ethane.

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(a) Using Al₂O₃ as dehydrating agent.

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[350\degree\text{C}]{\text{Al}_2\text{O}_3} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(b) Using hot conc. H₂SO₄

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(a) Colourless and inflammable gas.

(b) Faint sweetish odour.

(c) Slightly less dense than air.

(d) Sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform.

(a) ethyl bromide into ethene : Dehydrohalogenation

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \text{KBr} + \text{H}_2\text{O}$

(b) ethene into 1,2-dibromoethane : Halogenation

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}$

(c) ethene into ethane : Hydrogenation

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(a) ethene is burnt in excess of oxygen.

C₂H₄ + 3O₂ ⟶ 2CO₂ + 2H₂O + heat

(b) ethene reacts with chlorine gas.

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}$

(c) ethene combines with hydrogen chloride.

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{HCl (aq.)}\longrightarrow \underset{\text{chloroethane}}{\text{CH}_3\text{CH}_2\text{Cl}}$

(d) a mixture of ethene and hydrogen is passed over nickel at 200°C.

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(a) A — CH₃Cl (Chloro methane)

B — CH₂Cl₂ (Di-chloromethane)

C — CHCl₃ (Tri-chloro methane)

D — CCl₄ (Carbon tetrachloride)

CH₄ $\xrightarrow[\text{-HCl}]{\text{Cl}_2}$ CH₃Cl $\xrightarrow[\text{-HCl}]{\text{Cl}_2}$ CH₃Cl₂ $\xrightarrow[\text{-HCl}]{\text{Cl}_2}$ CHCl₃ $\xrightarrow[\text{-HCl}]{\text{Cl}_2}$ CCl₄

(b) A — C₂H₄ (ethene)

B — C₂H₆ (ethane)

C — C₂H₅Br (bromo-ethane)

D — C₂H₄Br₂ (1,2-Di-bromoethane)

C₂H₂ $\xrightarrow{\text{H}_2}$ C₂H₄ $\xrightarrow{\text{H}_2}$ C₂H₆ $\xrightarrow[\text{-HBr}]{\text{Br}_2}$ C₂H₅Br $\xrightarrow[\text{-HBr}]{\text{Br}_2}$ C₂H₅Br₂

(c) B — H₂ (Hydrogen)

C₂H₄ + H₂ $\xrightarrow[\text{Nickle}] {200\degree\text{C}}$ C₂H₆

(a) C₂H₄ + Cl₂ ⟶ Cl-CH₂-CH₂-Cl

Product formed is 1,2-dichloroethane[Cl-CH₂-CH₂-Cl]

(b) C₂H₅I + KOH (alc.) $\xrightarrow{\Delta}$ C₂H₄ + KI + H₂O

Product formed is ethene [C₂H₄], KI and water

(c) H₂C=CH₂ $\xrightarrow{\text{alk. KMnO}_4}$ CH₂(OH)-CH₂(OH)

Product formed is 1,2-Ethane-diol [CH₂(OH)-CH₂(OH)]

(d) H₂C=CH₂ + HBr ⟶ C₂H₅Br

Product formed is Bromoethane [C₂H₅Br]

Ethene is oxidised with alkaline KMnO₄ at room temperature, the purple colour of KMnO₄ decolourises.

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \underset{\text{ cold alkaline}}{\text{H-O-H} + \text{[O]}} \longrightarrow \underset{\text{1,2-Ethane-diol}}{\text{OH-CH}_2-\text{CH}_2\text{OH}}$

1. Polythene — carry bags are made.
2. Ethanol — cosmetics and toiletries preparation.
3. Oxy-ethylene torch — used for cutting and welding of metals.

2,2-Dimethylpropane

2-Methylbutane

Prop-1-ene

2,2-Dimethylpentane

Pent-2-yne

3-Methylbut-1-yne

2,3-Dichloropentane

3-Methylheptane

But-2-ene

Hept-2-yne

5,5-Dimethylhexanal

Pentan-2-ol

4-Methylpentanoic acid

2-Bromo-2-methylbutane

1-Bromo-3-methylbutane

Prop-1-yne

Methanal

3-ethyl-3,5-dimethylhexane

Propan-1-ol

Ethanoic acid

Ethanal

1,2-Dichloroethane

Prop-1-ene

2,3-dimethylbutane

2-methylpropane

3-hexene

Prop-1-yne

2-methylprop-1-ene

Alcohol with molecular formula C₄H₁₀O

(a) Alkyl group

Reason — It follows the formula C_nH_{2n + 1}

C₁₅H₃₀

Reason — According to the formula C_nH_2n, hydrogen is double of carbon, hence, C₁₅H₃₀ follows the formula C_nH_2n

2

Reason — The chain structures are shown below:

n-butane

Isobutane

Functional group isomers

Reason — CH₃-CH₂-OH is ethyl alcohol and contains Hydroxyl (OH) as the functional group.

CH₃-O-CH₃ is Dimethyl ether and contains Ether C-O-C as the functional group.

As the two have same molecular formula but different but different functional groups hence, they are called functional isomers.

3-methylhexane

Reason — As one methyl group is attached at the third carbon and the longest chain is of 6 carbon atoms, hence, the name is 3-methylhexane

(a) Propane and ethane are homologous.

(b) A saturated hydrocarbon does not participate in a/an addition reaction.

(c) Succeeding members of homologous series differ by CH₂.

(d) As the molecular masses of hydrocarbons increase, their boiling points increase and melting points increase.

(e) C₂₅H₅₂ and C₅₀H₁₀₂ belong to the same homologous series

(f) CO is an inorganic compound.

(g) The chemical properties of an organic compound are largely decided by the functional group and the physical properties of an organic compound are largely decided by the number of carbon atom.

(h) CHO is the functional group of an aldehyde.

(i) The root in the IUPAC name of an organic compound depends upon the number of carbon atoms in principal chain.

(j) But-1-ene and but-2-ene are examples of position isomerism.

Chain isomerism — When two or more compounds have a similar molecular formula but are different in the arrangement of carbon atoms in straight or branched chains the compounds are referred as chain isomers.

Example: Pentane C₅H₁₂

Pentane [n-pentane]

2-Methyl butane [iso-pentane]

2,2 Dimethyl Propane [neo-pentane]

Position isomers — When two or more compounds with the same molecular formula differ in the position of substituent atom or functional group on the carbon atom, they are called position isomers.

Example : But-1-yne and But-2-yne

But-1-yne

But-2-yne

Isomerism is the phenomenon due to which two or more compounds have the same molecular formula but differ in molecular arrangement or in structural formula.

Two main causes of isomerism are:

1. Difference is the mode of linking of atoms.
2. Difference in the arrangement of atoms or groups in space.

The chain isomers of hexane are shown below:

n-hexane

2 Methylpentane

3 Methylpentane

2,3 Dimethylbutane

2,2 Dimethylbutane

Position isomers of butene are shown below:

1-butene

2-butene

(a) isomer of n-butane is Isobutane. Its structural formula is shown below:

Isobutane

(b) Vinegar (acetic acid)

(c) 2-Propanol

(d) Ethanal

(e) Acetone

(f) Diethyl ether

These compounds together can be called organic compounds.

(g) Propanoic acid

(h) Pentan-2-ol

(i) 2,2 dibromo butane

(i) The special feature of the structure of ethene is that the two carbon atoms are linked by double covalent bond formed by sharing two pairs of electrons between the two carbon atoms.

(ii) The special feature of the structure of ethyne is that the two carbon atoms are linked by triple covalent bond formed by sharing three pairs of electrons between the two carbon atoms.

(b) The above compounds undergo addition reactions. Methane does not undergo this type of reaction as its all 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(c) Methoxymethane

(i) Ethane will undergo Substitution reactions.
Reason — In case of ethane, all of its 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(ii) Ethene will undergo Addition reactions.
Reason — In case of ethene, the valencies of atleast 2 carbon atoms are not fully satisfied by hydrogen atoms. The availability of electrons in the double bond makes them more reactive and hence they undergo addition reactions only.

The alkanes form a (a) homologous series with the general formula (b) C_nH_2n+2. The alkanes are (c) saturated (d) hydrocarbons which generally undergo (e) substitution reactions.

(a) Ethane : CH₃-CH₃

(b) Ethanol : C₂H₅OH

(c) Ethyne : C₂H₂

(a) Ethanol

(b) Ethanoic acid

(c) Ethene

(a) IUPAC name: Propanoic acid

Functional group: -COOH

(b) IUPAC name: Propanol

Functional group: -OH

(a) Alkenes are the (i) homologous series of (ii) unsaturated hydrocarbons. They differ from alkanes due to the presence of (iii) double bonds. Alkenes mainly undergo (iv) addition reactions.

(b) The organic compound which undergoes substitution reaction is (v) C₂H₆.

(c) The correct IUPAC names of isomers of Butane are Butane and 2-Methyl propane. Their structural formulae are given below:

1. Butane [n-butane]

2. 2-Methyl propane [iso-butane]

(a) Ethane [C₂H₆]

(b) Propan-1-ol [C₃H₇OH]

(c) Ethyne [C₂H₄]

Natural gas and petroleum are the principal sources of alkanes. Natural gas contains mainly methane with smaller amounts of ethane, propane and butane.

Methane is a primary constituent of natural gas. It absorbs outgoing heat radiations from the earth and thus contributes to the green house effect and so is considered as a green house gas. Methane remains in the atmosphere for approximately 10 years. It is twenty times more effective in trapping heat in comparison to carbon dioxide.

The general formula for alkanes is C_nH_2n+2, where n is the number of carbon atoms.

(a) Isomers of butane [C₄H₁₀]:

1. n-butane

2. Isobutane

(b) Isomers of pentane [C₅H₁₂]:

Pentane [n-pentane]

2-Methyl butane [iso-pentane]

2,2 Dimethyl Propane [neo-pentane]

(a) Molecular formula

Methane - CH₄

Ethane - C₂H₆

(b) Electron dot formula

Methane

Ethane

(c) Structural formula

Methane (CH₄)

Ethane(C₂H₆)

(a) Laboratory preparation of methane

A mixture of sodium ethanoate (sodium acetate) and soda lime is taken in a hard glass test tube and heated over a bunsen flame.

CH₃COONa + NaOH $\xrightarrow[300\degree\text{C}]{\text{CaO}}$ CH₄↑ + Na₂CO₃

The gas evolved is collected by downward displacement of water since it is slightly soluble in water and is lighter than air.

(b) Laboratory preparation of ethane

A mixture of sodium propionate and soda lime is taken in a boiling tube and heated over a bunsen flame.

C₂H₅COONa + NaOH $\xrightarrow[300\degree\text{C}]{\text{CaO}}$ C₂H₆↑ + Na₂CO₃

The gas evolved is collected by downward displacement of water.

Iodomethane (Methyl iodide) and bromoethane (ethyl bromide) are reduced by nascent hydrogen at ordinary room temperature.

CH₃I + 2[H] ⟶ CH₄ + HI

C₂H₅Br + 2[H] ⟶ C₂H₆ + HBr

Nascent hydrogen is produced by the action of Zn powder and dil. HCl or Zn/Cu couple in alcohol.

A reaction in which one atom of a molecule is replaced by another atom (or group of atoms) is called a substitution reaction.

e.g., CH₄ + Cl₂ ⟶ CH₃Cl + HCl

Reaction of chlorine with ethane is given below:

C₂H₆ + Cl₂ ⟶ C₂H₅Cl + HCl

The product formed is Monochloroetahne [C₂H₅Cl]

(a) The compounds formed are carbon dioxide and water

CH₄ + 2O₂[excess] ⟶ CO₂ + 2H₂O

(b) The compounds formed are carbon monoxide and water

2CH₄ + 3O₂[insufficient] ⟶ 2CO + 4H₂O

(a) Methane

(i) Reaction with chlorine: Chloromethane [CH₃Cl] and Hydrochloric acid [HCl] are formed when methane reacts with chlorine.

CH₄ + Cl₂ $\xrightarrow[\text{or 600K}]{\text{diffused sunlight}}$ CH₃Cl + HCl

(ii) Reaction with Bromine : Bromomethane [CH₃Br] and Hydrogen bromide [HBr] are formed when methane reacts with bromine.

CH₄ + Br₂ ⟶ CH₃Br + HBr

(b) Ethane

(i) Reaction with chlorine: Chloroethane [C₂H₅Cl] and Hydrochloric acid [HCl] are formed when ethane reacts with chlorine.

C₂H₆ + Cl₂ ⟶ C₂H₅Cl + HCl

(ii) Reaction with Bromine : Bromoethane [C₂H₅Br] and Hydrogen bromide [HBr] are formed when ethane reacts with bromine.

C₂H₆ + Br₂ ⟶ C₂H₅Br + HBr

(a) Sodium propionate : compound prepared are ethane and sodium carbonate

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[\Delta]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + \text{Na}_2\text{CO}_3$

(b) Methyl iodide : compound prepared are methane and hydrogen iodide

$\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} ↑ +\text{HI}$

(c) Ethyl bromide : compound prepared are ethane and hydrogen bromide

$\underset{\text{ethylbromide}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑+\text{HBr}$

(i) Methane:

CH₄ + 2O₂[excess] ⟶ CO₂ + 2H₂O

(ii) Ethane

2C₂H₆ + 7O₂[excess] ⟶ 4CO₂ + 6H₂O

(a) Methane into chloroform

$\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \underset{\Delta}{\xrightarrow{\text{diffused sunlight}}} \underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \text{HCl}$

$\underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \underset{\text{[excess]}}{\text{Cl}_2} \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{HCl}$

$\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane or chloroform}}{\text{CHCl}_3}+ \text{HCl}$

(b) Sodium acetate into methane

$\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3$

(c) Methyl iodide into ethane

$\underset{\text{methyl iodide}}{2\text{CH}_3\text{I}} + 2\text{Na} \xrightarrow{\text{dry ether}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + 2\text{NaI}$

(d) Methane to methyl alcohol

$\underset{\text{ methane}}{2\text{CH}_4} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{475 K Cu tube}} \underset{\text{methyl alcohol}}{2\text{CH}_3\text{OH}}$

(a) Methane

1. Methane is a source of carbon monoxide and hydrogen.
2. It is used in the preparation of useful compounds like ethyne, methanal, methanol, chloro-methane, and tetrachloro-methane.
3. It is employed as a domestic fuel.

(b) Ethane

1. It is used in the preparation of ethene, ethanol, ethanal and ethanoic acid.
2. It forms ethyl chloride, which is used to make tetraethyllead.
3. Ethane is also a good fuel.

(a) Ethyl alcohol — is produced when ethane and oxygen react at 120 atm pressure, 475 K temperature and pushed through copper tubes.

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

(b) Acetaldehyde — is produced when ethane and oxygen react by using catalyst MoO

$\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}$

(c) Acetic acid

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}$

Alcohol ⟶ Ethyl alcohol [C₂H₅OH]

Aldehyde ⟶ Acetaldehyde [CH₃CHO]

Acid ⟶ Acetic acid [CH₃COOH]

Ethane to an alcohol :

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

Ethane to an aldehyde :

$\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}$

Ethane to an acid :

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}$

Natural gas and petroleum are the sources of alkynes. The general formula of alkynes is : C_nH_2n-2

Isomers of Butyne exhibit position isomerism:

IUPAC name : but-1-yne

IUPAC name : but-2-yne

(a) Below diagram shows the setup for laboratory preparation of ethyne:

(b) Ethyne [C₂H₂] from Calcium Carbide :

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(b) As the pure dry gas is insoluble in water, it is collected by downward displacement of water.

When 1,2-dibromoethane [ethylene dibromide] is boiled with alcoholic potassium hydroxide, ethyne is formed.

$\underset{\text{ ethylene dibromide}}{\text{C}_2\text{H}_4\text{Br}_2} + \underset{\text{alcoholic}}{\text{2KOH}} \xrightarrow[\text{boiling}]{\text{200}\degree \text{C}} \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + 2\text{KBr} + 2\text{H}_2\text{O}$

(a) Methane

(b) Ethene

(c) Ethyne

(d) Ethyne

(e) Alkanes

(f) Alkenes

(g) Calcium carbide

• Alkanes — C₃H₈
• Alkenes — C₃H₆
• Alkynes — C₃H₄, C₅H₈

(a) On adding few drops of alkaline potassium permanganate (purple colour) to the hydrocarbons, no change is seen in saturated hydrocarbons whereas the purple colour fades in case of unsaturated hydrocarbons.

(b) When bromine is passed through solutions of ethane and ethene in an inert solvent [CCl₄] at room temperature, incase of ethene gas, brown colour of bromine is discharged whereas in case of ethane gas no change in the colour is observed.

(c) On adding ammoniacal silver nitrate, no change is seen in ethene whereas white ppt. of silver acetylide is formed in case of ethyne.

(a) Compound 'X' is Ethene (H₂C=CH₂). Its structural formula is shown below:

(b) Brown colour of bromine is discharged.

(a) An alkene to an alkane

$\underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(b) An alkene to an alcohol

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}$

(c) An alkyne to an alkene.

$\underset{\text{ ethyne [acetylene]}}{\text{H}_2\text{C}_2} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4}$

1,2-dichloro ethene and 1,1,2,2 -tetrachloro ethane will be formed.

C₂H₂ + Cl₂ ⟶ C₂H₂Cl₂ + Cl₂ ⟶ C₂H₂Cl₄

(b) Bromine

1,2-dibromo ethene and 1,1,2,2 -tetrabromo ethane will be formed.

C₂H₂ + Br₂ ⟶ C₂H₂Br₂ + Br₂ ⟶ C₂H₂Br₄

(c) Iodine

1,2-di-iodoethene will be formed.

C₂H₂ + I₂ ⟶ ICH=CHI

(d) Hydrogen

Ethene and then ethane will be formed.

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(e) Excess of hydrochloric acid.

Chloro ethene and then 1,1-dichloro ethane will be formed.

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} \xrightarrow{\text{+ HCl}} \underset{\text{chloro ethene}}{\text{C}_2\text{H}_3\text{Cl}} \xrightarrow{\text{+ HCl}} \underset{\text{1,1-dichloro ethane}}{\text{C}_2\text{H}_4\text{Cl}_2}$

Substitution reactions are characteristic reactions of alkanes.

(a) (i) Ethyne [C₂H₂] from Calcium Carbide :

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} ↑ + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(ii) An alcohol from ethyl bromide.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \text{KOH [aq.]} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{KBr}$

(b) Brown colour of bromine disappears when ethyne is bubbled through a solution of bromine in carbon tetrachloride.

C₂H₂ + Br₂ ⟶ C₂H₂Br₂ + Br₂ ⟶ C₂H₂Br₄

(c) Ethanol (C₂H₅OH)

C₂H₄ + H₂O ⟶ C₂H₅OH

(a) The two carbon atoms of ethyne form a triple covalent bond whereas that of ethene form a double covalent bond. Hence, there are more electrons available in case of ethyne making it more reactive than ethene.

(b) Ethene is an unsaturated hydrocarbon having two carbon atoms forming a double covalent bond as their valencies are not fully satisfied by hydrogen atoms whereas ethane is a saturated hydrocarbon as all the four valencies of its two carbon atoms are satisfied by the hydrogen atoms. The availability of electrons in the double bond in case of ethene makes it more reactive than ethane which has does not have electrons available in the single covalent bond.

(c) Hydrocarbons have high calorific value. They are easily combustible and the reaction is exothermic releasing heat energy. Hence, they are excellent fuels.

(i) C₄H₁₀ + 6O₂ ⟶ 4CO₂ + 5H₂O

(ii)

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(b) (i) Convert ethane to tetrabromoethane

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} \xrightarrow[(\text{from \text{C}\text{Br}}_4)]{\text{+Br}_2} \underset{\text{dibromoethene}}{\text{C}_2\text{H}_2\text{Br}_2} \xrightarrow[(\text{from \text{C}\text{Br}}_4)]{\text{+Br}_2} \underset{\text{tetrabromo ethane}}{\text{C}_2\text{H}_2\text{Br}_4}$

(ii) Convert ethyne to ethane.

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(a) Carbon tetrachloride from methane

$\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \xrightarrow[\text{or 600K}]{\text{diffused sunlight}} \text{CH}_3\text{Cl} + \text{HCl}$

$\underset{\text{ chloromethane} }{\text{CH}_3\text{Cl}} + \text{Cl}_2 \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2}+ \text{HCl}$

$\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane}}{\text{CH}\text{Cl}_3}+ \text{HCl}$

$\underset{\text{trichloromethane}}{\text{CHCl}_3} + \text{Cl}_2 \longrightarrow \underset{\text{tetrachloromethane}}{\text{CCl}_4}+ \text{HCl}$

(b) Structural formula of ethyne is shown below:

(c) Alkynes contain triple bonds while alkenes contain double bonds.

(a) Alcohols are the hydroxyl derivatives of alkane. They are formed by replacing one or more hydrogen atoms of the alkane with an OH group.

Alcohols are not found naturally in the earth's atmosphere, they are obtained by artificial synthesis in the laboratory.

For example, Methanol (wood spirit) is obtained from destructive distillation of wood, while ethanol is obtained from fermentation of sugar.

(b) C_nH_2n+1OH

(a) Methyl alcohol (CH₃OH) is the first member of alcohol. Its electron dot structure is shown below:

(b) Propyl alcohol : CH₃-CH₂-CH₂-OH

(c) Ethyl alcohol : CH₃-CH₂-OH

(d) Butyl alcohol : CH₃-CH₂-CH₂-CH₂-OH

(a) Hydrolysis of ethene — Ethanol is produced when ethene is heated with water at 300°C and 60 atmosphere pressure in presence of phosphoric acid (catalyst).

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}}$

(b) Hydrolysis of ethyl bromide — Ethanol can be prepared by boiling aq. NaOH with ethyl bromide.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

Ethyl alcohol can be prepared by hydrolysis of haloalkane on reaction with hot and dilute alkali or when an alkyl halide is boiled with aqueous alkalis.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

(a) The boiling point and melting point increase with increasing molecular weight in the homologous series of alcohols.

(b) Ethyl acetate is generated when ethanol combines with acetic acid.

$\underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow[\Delta]{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}$

(c) Esterification.

(a) H-C≡C-H + H₂ ⟶ H₂C=CH₂ + H₂ ⟶ H₃C-CH₃

(b) C₂H₄ + Br₂ ⟶ Br-CH₂-CH₂-Br

(c) C₂H₄ + HCl ⟶ CH₃CH₂Cl

(d) CaC₂ + 2H₂O ⟶ C₂H₂↑ + Ca(OH)₂

(e) C₂H₂ + Br₂ ⟶ C₂H₂Br₂

(f) C₂H₅OH $\xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}}$ CH₃CHO

Ethanol affects the part of the brain which controls our muscular movements. It gives temporary relief from tiredness, but it damages the liver and kidney too in excess quantities.

(a) Absolute alcohol — By distilling wet alcohol with benzene, absolute alcohol can be obtained. The mixture of water and benzene distils off, leaving behind anhydrous alcohol.

(b) Spurious alcohol — It is illicit liquor made by improper distillation. It contains large proportions of methanol in a mixture of alcohols.

It's a blend of alcohol with a lot of methanol in it. It is fatal for human consumption.

(c) Methylated spirit — Ethyl alcohol is mixed 5% methyl alcohol, a coloured dye, and some pyridine to obtain methylated spirit.

(a) When sodium reacts with ethyl alcohol, hydrogen is produced, and sodium ethoxide is formed.

C₂H₅OH + 2Na ⟶ 2C₂H₅ONa + H₂ ↑

(b) Ethanol is oxidised and transformed to ethanal, which is then turned to acetic acid.

$\underset{ \text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal}}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanoic acid}}{\text{CH}_3\text{COOH}}$

Ethanol under high pressure and low temperature when treated with oxidising agent like acidified potassium dichromate produces ethanoic acid

$\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}$

(a) Ethyne

(b) Ethyne

(c) Methanol

(d) Methanol

(e) Ethanol

(f) Ethanol

(g) Ethanol

(h) Ethanol

(a) The conversion of ethanol into ethene is an example of dehydration

(b) Converting ethanol into ethene requires the use of conc. H₂SO₄

(c) The conversion of ethene into ethane is an example of hydrogenation

(d) The catalyst used in the conversion of ethene into ethane is commonly nickel

(a) Ethane [C₂H₆] from sodium propionate:

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3$

(b) Ethene from iodoethane:

$\underset{\text{ iodoethane}}{\text{C}_2\text{H}_5\text{I}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KI} + \text{H}_2\text{O}$

(c) Ethyne from calcium carbide:

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \text{Ca(OH)}_2$

(d) Methanol from idomethane.

$\text{CH}_3\text{I} + \text{NaOH} \longrightarrow \text{CH}_3\text{OH} + \text{NaI}$

(i) Ethane

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3$

(ii) Methane

$\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} +\text{HI}$

(iii) Ethene [ethylene]

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KBr} + \text{H}_2\text{O}$

(iv) Methanol

$\text{CO} + 2\text{H}_2 \xrightarrow[\text{catalyst}]{\text{Zinc oxide}} \text{CH}_3\text{OH}$

(v) Ethyne [Acetylene]

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(a) Water is added to calcium carbide:

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(b) Ethene and water (steam).

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}$

(c) Bromoethane and an aqueous solution of sodium hydroxide.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

An organic compound containing the carboxyl group (-COOH) is known as carboxylic acid. These compounds possess acidic properties.

General formula : C_nH_2n+1COOH (or RCOOH)

(a) First three members of carboxylic acid series are:

1. Methanoic acid (formic acid)
2. Ethanoic acid (acetic acid)
3. propanoic acid (propionic acid)

(b) Three compounds which can be oxidised directly, or in stages to produce acetic acid are:

1. Ethanol
2. Acetylene
3. Ethanal

(a) Structural formula of acetic acid is shown below:

(b) Ethanoic acid

(c) Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous (water-free) acetic acid or glacial acetic acid. Its melting point is around 17°C. On cooling it forms a crystalline mass resembling ice and for this reason it is called glacial acetic acid.

Dilute (4-5 percent) solution of ethanoic acid is also called vinegar. The presence of a colouring matter gives vinegar a greyish colour while the presence of other organic compounds imparts it the usual taste and flavour.

(a) Vinegar is prepared by the bacterial oxidation of ethanol

(b) The organic acid present in vinegar is acetic acid

(c) The next higher homologue of ethanoic acid is propanoic acid

(a) Ethanol under high pressure and low temperature when treated with oxidising agent like acidified potassium dichromate produces ethanoic acid (acetic acid).

$\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}$

(b) Acetylene is first converted to acetaldehyde by passing it through a 40 percent H₂SO₄ solution at 60°C in the presence of 1% Mercury(II) Sulphate [HgSO₄].

$\underset{\text{acetylene}}{\text{C}_2\text{H}_2} + \text{H}_2\text{O} \xrightarrow{\text{H}_2\text{SO}_4\text{(dil) , HgSO}_4}\underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}}$

The acetaldehyde is oxidised to acetic acid by passsing a mixture of acetaldehyde vapous and air over manganese acetate at 70°C

$\underset{\text{ethanal [acetaldehyde] }}{2\text{CH}_3\text{CHO}} + \text{O}_2 \xrightarrow[\text{Catalyst}]{\Delta} \underset{ \text{ethanoic acid[acetic acid]} }{2\text{CH}_3\text{COOH}}$

(a) Acetic acid turns moist blue litmus red.

(b) Hydrogen gas with a pop sound is evolved.

2CH₃COOH + Zn ⟶ (CH₃COO)₂Zn + H₂ ↑

(c) Reacts with alkalis to form salt and water.

CH₃COOH + NaOH ⟶ CH₃COONa + H₂O

(d) Forms an ester (pleasant fruity smelling compound) on reacting with alcohol in the presence of dehydrating agents like concentrated sulphuric acid.

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{CH}_3\text{COOH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{{\text{CH}_3\text{COOC}_2\text{H}_5}} + \text{H}_2\text{O}$

(a) a metal

2CH₃COOH + Zn ⟶ (CH₃COO)₂Zn + H₂ ↑

(b) a base/alkali

CH₃COOH + NaOH ⟶ CH₃COONa + H₂O

(c) a carbonate

2CH₃COOH + Na₂CO₃ ⟶ 2CH₃COONa + H₂O + CO₂ ↑

(d) a bicarbonate

CH₃COOH + NaHCO₃ ⟶ CH₃COONa + H₂O + CO₂ ↑

(a) Carbon dioxide is produced when acetic acid is added to sodium bicarbonate.

(b) When warmed with ethyl alcohol in the presence of sulphuric acid, a pleasant fruity smell of ethyl acetate is produced.

(c) On adding acetic acid to neutral FeCl₃ solution, wine red colour is produced.

(a) Ethyl acetate

(b) Phosphorus pentoxide (P₂O₅)

(a) Organic compounds are the compounds of carbon excluding oxides of carbon, metallic carbonates and related compounds like metal cyanides, metal carbides, etc.

(b) As organic compounds were obtained straight from nature and there was no known method of preparing them in the laboratory, hence it was believed that they were the products of some vital force of nature. This theory was known as vital force theory.

This theory was soon discarded when in 1828, Friedrich Wohler demonstrated that an organic chemical (urea) could be produced in the laboratory.

(a) Sources of organic compounds are:

1. Plants
2. Animals
3. Coal
4. Petroleum
5. Fermentation
6. Wood
7. Synthetic methods

(b) Organic chemistry is used in the manufacturing of soaps, shampoos, powders, and perfumes. The clothes we wear, the food we eat i.e., carbohydrates, proteins, fats, vitamins etc.,fuels we use, natural gas, petroleum products, medicines, explosives, dyes, insecticides,etc., are all organic compounds. There is hardly any walk of life where we do not use organic compounds.

Organic chemistry is extremely useful to us in our daily life.

The soaps and shampoos we use while taking bath, the powders, perfumes, etc., we apply on the body, the clothes we wear, food we eat i.e., carbohydrates, proteins, fats, vitamins etc., fuels we use, natural gas, petroleum products, medicines, explosives, dyes, insecticides, etc., are all organic compounds. There is hardly any walk of life where we do not use organic compounds.

Unique properties of carbon are :

1. Tetravalency of carbon
2. Catenation

(a) Tetravalency : Carbon has four valence electrons (At. no. of C = 6; Electronic Config. 2,4). Since it can neither lose nor gain electrons to attain octet, it forms covalent bonds by sharing it's four electrons with other atoms. This characteristics of the carbon atom , by virtue of which it forms four covalent bonds , is called the tetravalency of carbon.

(b) Catenation : The property of self linking of atoms of an element through covalent bonds in order to form straight chains, branched chains and cyclic chains of different sizes is known as catenation.

The unique nature of carbon atom (catenation and tetravalency) gives rise to the formation of a large number of compounds. More than 5 million organic compounds are known today and thousand are added every year. Hence, it demands a new field of chemistry i.e., organic chemistry.

Hydrocarbons are compounds that are made up of only carbon and hydrogen atoms.

Carbon shows unique properties of tetravalency and catenation. Due to this unique nature of carbon atoms, they form single, double and triple covalent bonds with other carbon atoms and a variety of other elements. Carbon atoms have the ability to form stable bonds with other atoms resulting in the formation of long chains, branched structures, and cyclic compounds. These properties of carbon atom gives rise to the formation of a large number of compounds.

(a) Single bond compound : C₄H₁₀ has two chain isomers

1. n-butane

2. Isobutane

(b) Double bond compound : C₄H₈ has two position isomers

1. But-1-ene

2. But-2-ene

(c) Triple bond compound : C₄H₆ has two position isomers

1. But-1-yne

2. But-2-yne

(a) Cyclopropane [C₃H₆]

(b) Cyclopentyne [C₅H₆]

(a) Methane

(b) Ethene

Substitution reactions — A reaction in which one atom of a molecule is replaced by another atom (or group of atoms) is called a substitution reaction.

e.g., CH₄ + Cl₂ ⟶ CH₃Cl + HCl

Addition reactions — A reaction involving addition of atoms or molecules to the double or the triple bond of an unsaturated compound so as to yield a saturated product is known as addition reaction.

e.g., C₂H₄ + Br₂ ⟶ C₂H₄Br₂

Functional group is defined as an atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds.

The structural formula of the functional groups are given below:

(a) $\overset{\underset{\text{||}}{\text{O}}}{\text{-C-}}$

(b) -OH

(c) -CH=O

(a) A homologous series is a group of organic compounds having a similar structure and similar chemical properties in which the successive compounds differ by a CH₂ group.

(b) The difference in the molecular formula of two adjacent homologues:

1. In terms of molecular mass is 14 a.m.u.
2. In terms of number & kind of atoms per molecule is that each member of the series differs from the preceding one by the addition of CH₂ group.

(a) Butyne C₄H₆

(b) Butanol C₄H₉OH

(i) Alkyl group

(ii) Functional group

(a) An alkyl group of atoms is obtained by removing one atom of hydrogen from an alkane molecule.

(b) Three alkyl radicals are:

1. Methyl
2. Ethyl
3. Propyl

These are formed by losing one hydrogen atom

CH₄ ⟶ CH₃ + H

C₂H₆ ⟶ C₂H₅ + H

C₃H₈ ⟶ C₃H₇ + H

First three members of the homologous series of alkanes are :

1. Methane (CH₄)

2. Ethane(C₂H₆)

3. Propane (C₃H₈)

(a) CH₃OH

Alkyl radical — Methyl (-CH₃)

Functional group — Alcohol (-OH)

(b) C₂H₅OH

Alkyl radical — Ethyl (-C₂H₅)

Functional group — Alcohol (-OH)

(c) C₃H₇CHO

Alkyl radical — Propyl (-C₃H₇)

Functional group — Aldehyde (-CHO)

(d) C₄H₉COOH

Alkyl radical — Butyl (-C₄H₉)

Functional group — carboxyl (-COOH)

(e) CH₃COOH

Alkyl radical — Methyl (-CH₃)

Functional group — carboxyl (-COOH)

(f) C₂H₅Br

Alkyl radical — Ethyl (-C₂H₅)

Functional group — Bromine (-Br)

They can undergo addition as well as substitution reaction.

Reason — The non-availability of electrons in the single covalent bond makes them less reactive and therefore undergo characteristic substitution reaction only.