Chemistry

Hydrocarbons

Question:

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

Answer:

The formation of two moles of an aldehyde indicates the presence of identical structural units on both sides of the double bond containing carbon atoms. Hence, the structure of ‘A’ can be represented as:  XC = CX
There are eight C-H σ bonds. Hence, there are 8 hydrogen atoms in ‘A’. Also, there are three C-C bonds. Hence, there are four carbon atoms present in the structure of ‘A’.
The IUPAC name of ‘A’ is But-2-ene.
Ozonolysis of ‘A’ takes place as:
ncert-solutions-class-11th-chemistry-chapter-13-hydrocarbons-55

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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.

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 5.

What happens when ethanol is heated with cone. H2SO4?

Q 6.

What are conformations?

Q 7.

Which is more acidic: ethene or ethyne and why?

Q 8.

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

Q 9.

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 10.

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

Q 11.

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 12.

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

Q 13.

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 14.

How will you distinguish between propene and propane?

Q 15.

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 16.

What are Arenes ?

Q 17.

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

Q 18.

What is polymerization? Give an example.

Q 19.

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

Q 20.

Discuss the shape of methane and ethane.

Q 21.

What happens when benzene is treated with excess of Cl2 in presence of sunlight? Give chemical reaction.

Q 22.

What do you mean by pyrolysis?

Q 23.

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

Q 24.

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

Q 25.

ncert-solutions-class-11th-chemistry-chapter-13-hydrocarbons-34

Q 26.

What is Lindlar’s catalyst? Give its use.

Q 27.

(a) Why are alkenes called unsaturated hydrocarbons?
(b) How will you test the presence of double bond in an alkene?
(c) Name the products formed when propene is subjected to ozonolysis.

Q 28.

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

Q 29.

Suggest a route for the preparation of nitrobenzene starting from acetylene.

Q 30.

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

Q 31.

Write down the products ofozonolysis ofl, 2-dimethylbenzene (o-xylene). How does the result support Kekule structure of benzene?

Q 32.

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

Q 33.

Suggest the name of another Lewis acid instead of anhydrous aluminium chloride which can be used during ethylation of benzene.

Q 34.

What is decarboxylation ? Give an example.

Q 35.

Why are alkanes called paraffins?

Q 36.

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

Q 37.

How will you distinguish between acetylene and ethylene?

Q 38.

What is electrophile in sulphonation?

Q 39.

Classify the following compounds into (i) alkanes (ii) alkenes (iii) alkynes (iv) arenes.  (a) C6H6 (b) C4H8 (C) C8H8 (d) C5H8 (e) C6H14

Q 40.

Which are the correct IUPAC names of the following compound
ncert-exemplar-problems-class-11-chemistry-chapter-13-hydrocarbons-20

(a) 5-(2′,2′-Dimethylpropyl)decane
(b) 4-Butyl-2,2-dimethylnonane
(c) 2,2-Dimethyl-4-pentyloctane
(d) 5-neo-Pentyldecane

Q 41.

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

Q 42.

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

Q 43.

Which type of isomerism is exhibited by but-l-yne and but-2-yne?

Q 44.

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

Q 45.

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 46.

An alkene ‘A’ contains three C—C, eight C—H, a-bonds, and one C—C n-bond. ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write the IUPAC name of’A’.

Q 47.

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

Q 48.

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

Q 49.

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 50.

Arrange the following carbanions in order of their decreasing stability.
(A) H3C-C ≡ C–                                                                                
(B) H-C ≡ C–
(C) H3C – CH–2
(a) A>B>C
(b) B>A>C
(c) C>B>A
(d) C>A>B