Chapter 13 - Hydrocarbons

Assertion (A) : Among isomeric pentanes, 2, 2-dimethylpentane has highest
boiling point.
Reason (R) : Branching does not affect the boiling point.
(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.

Assertion (A) : Toluene on Friedal Crafts methylation gives o– and p–xylene.
Reason (R) : CH3-group bonded to benzene ring increases electron density
at o– and p– position.
(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.

Match the hydrocarbons in Column I with the boiling points given in Column II.
Column I Column II
(i) n–Pentane (a) 282.5 K
(ii) iso-Pentane (b) 309 K
(iii) neo-Pentane (c) 301 K

The relative reactivity of 1°, 2°, 3° hydrogen’s towards chlorination is 1 : 3.8 : 5.
Calculate the percentages of all monochlorinated products obtained from
2-methylbutane.

Despite their - I effect, halogens are o- and p-directing in haloarenes. Explain.

The intermediate carbocation formed in the reactions of HI, HBr and HCl with
propene is the same and the bond energy of HCl, HBr and HI is 430.5 kJ mol–1,
363.7 kJ mol–1 and 296.8 kJ mol–1 respectively. What will be the order of
reactivity of these halogen acids?

Rotation around carbon-carbon single bond of ethane is not completely free.
Justify the statement.

2-Butene is capable of showing geometrical isomerism.

Why do alkenes prefer to undergo electrophilic addition reaction while arenes
prefer electrophilic substitution reactions? Explain.

How will you convert benzene to hexachlorobenzene?

Name some carcinogenic hydrocarbons.

How is benzene converted to benzene hexachloride?

p-chloro nitro benzene has less dipole moment (2.4 D) than p-nitro toluene
(4.4 D). Why?

How will you distinguish between Ethene and benzene

What are electrophilic substitution reactions?

How will you convert benzene to iodobenzene? Give chemical equation.

What happens when benzene is oxidized at 770K in presence of V₂O₅? Give

chemical equation.

How will you convert benzene into
(i) p – Nitro bromo benzene
(ii) m – Nitrochloro benzene
(iii) p – Nitro toluene
(iv) Aceto phenone?

What is friedel craft’s reaction? Give an example.

How would you prepare benzene from lime?

Why is benzene extra ordinarily stable though it contains three double
bounds?

How will you convert the following compounds into benzene?
(i) ethene (ii) hexane.

How will you convert the following compounds to benzene?
(i) Acetylene (ii) Benzoic acid
(iii) Cyclohexane (iv) Benzene diazonium chloride.

How would you convert ethanoic acid into benzene?

How is phenol reduced to benzene?

How is benzene prepared from aromatic acids?

How will you account for the structure of benzene?

Give some examples of aromatic compounds.

How is aromaticity of a compound judged?

How is aromaticity of a compound judged?

Although benzene is highly unsaturated; it does not undergo addition
reactions. Give reason.

What do you understated by Resonance energy?

What do you mean by delocalization?

What are benzenoids?

How will you prepare 3-methyl but -1 – yne by starting with ethyne?

How will you convert ethyne to benzene?

Write combustion reaction for hexyne.

Convert 2- butyne to trans – 2- butane.

How will you convert ethyne to ethane?

How will you convert propyne to propanone?

How would you carry out the following conversion propene to ethyne.

Butanone is formed when an alkyne is passed through a dil sol of H₂SO₄ at 330K in

presence of mercuric sulphate. Write the possible structure of the alkyne.

How would you distinguish between butyne – 1 and butyne – 2?

Ethyne is acidic in nature in comparison to ethene and ethane. Why is it so?

Ethyne is acidic in nature in comparison to ethene and ethane. Why is it so?

Write the conversion of ethene to ethyne.

Although acetylene is acidic in nature, it does not react with NaOH or KOH.
Give reason?

How will you distinguish between ethylene and methane?

How is alkyne prepared from vicinal dihalides?

Write structures of different isomers formed by C₆H₁₀. Also write IUPAC

names of the all the isomers.

How is alkyne prepared by Kolbe’s method?

How is alkyne prepared from calcium carbide?

Name the simplest alkyne.

Write the general formula for alkynes.

Give the different isomers formed by C₅H₈ along with their IUPAC name.

Why do alknes not show geometrical isomerism?

What is the number of σ and π bond in
N ≡ C – CH = CH – C ≡ N?

Draw the orbital picture of ethyne showing.
(a) sigma overlaps
(b) pi – overlaps.

State kharasch effect.

Explain the term polymerization with two examples.

How will you distinguish between butene – 1 and butene – 2?

Write IUPAC name of the products obtained by addition reactions of HBr to
hex – 1 – ene.
(i) in the absence of peroxide, and
(ii) in the presence of peroxide.

Write the chemical equations of reactions involved in ozonolysis of alkenes.

Discuss the hybridization of carbon atoms in alkene C3H4 and show the π-
orbital overlaps.

Stale Markownikov’s Rule.

How are cis – alkenes formed by alkynes?

How are trans alkenes formed by alkynes?

How is alkene prepared from alcohol by acidic dehydration?

What is β-elimination reaction?

Arrange the following halogen atom to determine rate of the reaction.
Iodine, chlorine. Bromine.

How is alkene produced by vicinal dihalide?

How is alkene produced by Kolbe’s electrolytic method?

What is a Lindlars’ catalyst?

What are geometrical isomers?

Why will C₆H₅CH =CH – CH₃ show cis – trans isomerism?

Dipole moment of cis – but – 2 – ene is 0.33 D whereas dipole moment of the
trans form is almost zero. Why?

The physical properties of geometrical isomers are different while those
optical isomers are same. Why?

What is the shape of CH₂ = CH₂?

Which of the two exhibit geometrical isomerism? 2-Butene or 1Butene

What is the origin of geometrical isomerism in alkenes?

Draw orbital picture of ethane depicting σ-bond only.

Why is alkene considered a weaken molecule than alkane?

How is iso-butane prepared?

How would you convert cyclohexane to benzene?

Explain wurtz reaction with an example.

When alkanes are heated, the C-C bonds rather than the C-H bonds break. Give
reason.

All the four C-H bonds in methane are identical. Give reasons.

The dipole moment of trans 1,2-dichloroethane is less than the cis – isomer.
Explain.

Draw the New man’s projection formula of the staggered form of 1,2-dichloro
ethane.

Which conformation of ethane is more stable?

Pentane has three isomers i.e; pentane, 2-methyl butane and 2,2-dimethyl
propane . The b.p of pentane is 309.1K whereas 2,2-dimethyl propane shows a
b.p of 282.5k. Why?

The boiling point of alkanes shows a steady increase with increase in
molecular mass. Why?

N – pentane has higher boiling point than neopentane but the melting point
of neopentane is higher than that of n – pentane.

How will you prepare isobutane?

Cyclobutane is less reactive than cyclopropane. Justify.

Sodium salt of which acid will be needed for the preparation of propane?
Write chemical equation for the reaction.

Methane does not react with chlorine in dark. Why?

Give the IUPAC name of the lowest molecular weight alkane that contains a
quaternary carbon.

How would you convert ethene to ethane molecule?

What is hydrogenation section?

Write IVPAC names of the following

CH₃ (CH₂)₄ CH (CH₂)₃ CH₃

CH₂ – CH (CH₃)₂.

Draw all the possible structural isomers with the molecular formula C₆H₁₄,

Name them.

Draw the structure of the following compounds all showing C and H atoms.
(a) 2-methyl -3-iso propyl heptanes
(b) Dicyclopropyl methane.

Draw the structure of the following compounds all showing C and H atoms.
(a) 2-methyl -3-iso propyl heptanes
(b) Dicyclopropyl methane.

To which category of compounds does cyclohexane belong?

Why carbon does have a larger tendency of catenation than silicon although
they have same number of electrons?

Unsaturated compounds undergo addition reactions. Why?

The boiling point of hydrocarbons decreases with increase in branching. Give
reason.

What are cycloalkanes?

Classify the hydrocarbons according to the carbon – carbon bond

Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example.

Suggest the name of a Lewis acid other than anhydrous aluminium chloride which can be used during ethylation of benzene.

Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?

Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E⁺

(a) Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene

(b) Toluene, p-H₃C-C₆H₄-NO₂, p-O₂N-C₆H₄-NO₂.

Write structures of all the alkenes which on hydrogenation give 2-methylbutane.

How would you convert the following compounds into benzene?

(i) Ethyne (ii) Ethene (iii) Hexane

Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?

Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.

Write down the products of ozonolysis of 1, 2-dimethylbenzene (o-xylene). How does the result support Kekulé structure for benzene?

Addition of HBr to propene yields 2-bromopropane, while in the presence of benzoyl peroxide, the same reaction yields 1-bromopropane. Explain and give mechanism.

What effect does branching of an alkane chain has on its boiling point?

In the alkane H₃C-CH₂-C(CH₃)₂-CH₂-CH(CH₃)₂, identify 1°,2°,3° carbon atoms and give the number of H atoms bonded to each one of these.

Explain why the following systems are not aromatic?

(i)

(ii)

(iii)

What are the necessary conditions for any system to be aromatic?

Why is benzene extra ordinarily stable though it contains three doublebonds?

Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?

Write chemical equations for combustion reaction of the following hydrocarbons:

(i) Butane  (ii) Pentene (iii) Hexyne (iv) Toluene

Propanal and pentan-3-one are the ozonolysis products of an alkene? What is the structural formula of the alkene?

An alkene 'A' contains three C - C, eight C - H ÃÆ’ bonds and one C - C Ã€ bond. 'A' on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of 'A'.

An alkene 'A' on ozonolysis gives a mixture of ethanal and pentan-3-one. Write structure and IUPAC name of 'A'.

Write IUPAC names of the products obtained by the ozonolysis of the following compounds:

(i) Pent-2-ene (ii) 3,4-Dimethyl-hept-3-ene

(iii) 2-Ethylbut-1-ene (iv) 1-Phenylbut-1-ene

For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated:

(a) C₄H₈ (one double bond)

(b) C₅H₈ (one triple bond)

Write IUPAC names of the following compounds:

a. 

b. 

c. 

d. 

e. 

f.

g.

How do you account for the formation of ethane during chlorination of methane?