Chemistry

Hydrocarbons

Question:

What will be the product obtained as a result of the following reaction and why?

ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-32

Answer:

ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-33

Propyl chloride forms CH3 – CH2 – CH+2 with anhydrous A1C13 which is less stable. This rearranges to a more stable carbocation as:
ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-34

 

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Hydrocarbons

Q 1.

In the alkane, CH3CH2—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.

Q 2.

Convert ethylene to ethane.

Q 3.

What is the hybridisation of central carbon in 1,2-propadiene (CH2=C=CH2)?

Q 4.

How will you distinguish between propene and propane?

Q 5.

Nucleophiles and electrophiles are reaction intermediates having electron rich and electron deficient centres respectively. Hence, they tend to attack electron deficient and electron rich centres respectively. Classify the following species as electrophiles and nucleophiles.
ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-46

Q 6.

What happens when ethanol is heated with cone. H2SO4?

Q 7.

Arrange the following: HCl, HBr, HI, HF in order of decreasing reactivity towards alkenes.

Q 8.

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

Q 9.

Which of the following are correct?
(a) CH3 – O – CH+2 is more stable than CH3 – CH+2
(b) (CH3)2CH+ is less stable than CH3 – CH2 – CH+2
(c) CH2 = CH – CH+2 is more stable than CH3 – CH2 – CH+2
(d) CH2 = CH+ is more stable than CH3 – CH+2
 

Q 10.

What happens when benzene is treated with acetyl chloride in presence of AlCl3?

Q 11.

What will be the product obtained as a result of the following reaction and why?

ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-32

Q 12.

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)

Q 13.

Define resonance energy. What is resonance energy of benzene?

Q 14.

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

Q 15.

What is polymerization? Give an example.

Q 16.

How will you demonstrate that double bonds of benzene are somewhat different from that of olefins?

Q 17.

Arrange the following alkyl halides in decreasing order of the rate of β -elimination reaction with alcoholic KOH.

ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-10

Q 18.

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will butene formed on the reduction of but-2-yne show geometrical isomerism?

Q 19.

Despite their -I effect, halogens are o- andp-direction in haloarenes. Explain.

Q 20.

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.

Q 21.

What are conformations?

Q 22.

Discuss the preparation of alkanes by Wurtz reaction. What is the limitaHon of the reaction?

Q 23.

The molecules having dipole moment are________ .
(a) 2,2-Dimethylpropane                                            
(b) trans-Pent-2-ene
(c) cw-Hex-3-ene            
(d) 2,2,3,3-Tetramethylbutane

Q 24.

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

Q 25.

Write chemical equations for the combustion reaction of the following hydrocarbons,  (i) Butane (ii) Pentene (iii) Hexyne (iv) Toluene

Q 26.

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

Q 27.

What is Lindlar’s catalyst? Give its use.

Q 28.

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

Q 29.

Which of the following reactions of methane is incomplete combustion?
ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-13

Q 30.

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

Q 31.

Why are alkanes called paraffins?

Q 32.

Although benzene is highly unsaturated it does not undergo addition reactions. Why?

Q 33.

Explain the following with examples:
(i) Wurtz reaction
(ii) Hydrogenation.

Q 34.

Explain the term aromaticity. What are the necessary conditions for any compound to show aromaticity?

Q 35.

Arrange the following carbanions in order of their decreasing stability.
(A) H3C-C ≡ C                                                                                
(B) H-C ≡ C
(C) H3C – CH2
(a) A>B>C
(b) B>A>C
(c) C>B>A
(d) C>A>B

Q 36.

The intermediate carbocation formed in the reactions of HI, HBr and HC1 with propene is the same and the bond energy of HCl, HBr and HI is 430.5 kJ mol-1,363.7 kJ mol1 and 296.8 kJ mol-1 What will be the other of reactivity of these halogen acids?

Q 37.

What is decarboxylation ? Give an example.

Q 38.

Which is more acidic: ethene or ethyne and why?

Q 39.

How will you distinguish between acetylene and ethylene?

Q 40.

What is electrophile in sulphonation?

Q 41.

Write the IUPAC names of the following compounds.
(i) (CH3)CCH2C(CH3)3    (ii) (CH3)2C(C2H5)2

Q 42.

(a) What effect the branching of an alkane has on its melting point?
(b) Which of the following has highest boiling point?
(i) 2-methyl pentane
(ii) 2, 3-diethyl butane
(iii) 2, 2-dimethyl butane

Q 43.

How will you separate propene from propyne?

Q 44.

Draw Newman and Sawhorse projections for the eclipsed and staggered conformations of ethane. Which of these conformations is more stable and why? .

Q 45.

Why does the presence of a nitro group-make the benzene ring less reactive in comparison to the unsubstituted benzene ring? Explain.

Q 46.

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

Q 47.

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

Q 48.

Explain why the following systems are not aromatic?
ncert-solutions-class-11th-chemistry-chapter-13-hydrocarbons-17

Q 49.

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

Q 50.

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