12th Class Chemistry Chapter 9 Short Questions with Answers Solved

Question: 1

What are monocyclic and polycyclic aromatic Hydrocarbons?

Answer: 1

1-22

Monocyclic: Aromatic hydrocarbons containing one benzene ring in their molecules are called monocyclic aromatic hydrocarbons e.g benzene,toluene phenol,aniline benzoic acid,benzaldehyde and benzene sulphonic acid.

Question: 2

What information are obtained about structure of benzene from X-ray studies?

Answer: 2

2-22

The X-ray studies of benzene have confirmed the hexagonal structure of it.These studies have also revealed that all the carbon and hydrogen atoms are in the same plane.All the angles are of 120^o.All C-C and C-H bonds lengths are 1.397 A^oand 1.09A^orespectively.

Question: 3

What are aromatic hydrocarbons?Give two example.

Answer: 3

3-22

The carbocyclic compounds containing at least one benzene ring,six carbon atoms with three alternate double and single bonds are called aromatic hydrocarbons.These bonds are usually shown in the form of a circle.
Examples: Toluene,Phenol and Nitrobenzene.

Question: 4

What is Wurtz -Fritting reaction?

Answer: 4

4-22

The Wurtz reaction for the synthesis of alkanes was extended by Fitting in 1864 to the synthesis of alyl aromatic hydrocarbons.

Question: 5

Why benzene is less reactive than alkenes although it has three pi bonds in it?

Answer: 5

5-22

Benzene is extraordinary stable molecule,This stability is due to the extensive delocalization of pi electron.The unhybridized orbital partially overlap to form a continue sheath of electron cloud,enveloping above and below the six carbon carbon sigma bonds of the ring,

Question: 6

What are the major product when chlorine reacts with Toluene in the presence of sunlight?

Answer: 6

6-22

When alkyl benzene are treated with chlorine or bromine in the presence of sunlight ,only the alkyl groups are submitted.

Question: 7

Define resonance energy?What is the resonance energy of benzene?

Answer: 7

7-22

Benzene is more stable than the hypothetical 1,3,5-cyclohexatriene by 150.5 kj/mole.This difference between amount of heat is actually released and that calculated on the basis of the Kekule structure is called Resonance Energy Benzene shows the phenomenon of resonance which makes it more stable than others.In benzene electrons are delocalized making it a very stable molecule.The resonance energy of benzene is 150.5 kj/mole

Question: 8

What is resonance?

Answer: 8

8-22

The possibility of different pairing schemes of valence electrons of atom is called resonance and the different thus arranged are called "Resonance Structure.".

Question: 9

What objective were raised on Kekule formula of Benzene?

Answer: 9

9-22

Kekula formula with three double bonds demands of high degree of unsaturation from benzene while usually it exhibits a saturated character,This benzene yields substitution products readily and from addition products .Benzene is also very stable compound.

Question: 10

Define two reaction which show that Benzene is an unsaturated hydrocarbons?

Answer: 10

10-22

Benzene is reduced to cyclohexane on heating at high temperature with hydrocarbons in the presence if Pt in an acidic solvent or Ni at 200 Degree as a catalyst,This reaction show that benzene is Un-saturated compound.

Halogenation: Benzene reacts with chlorine and bromine in the presence of sunlight to give addition products ,hexechlorobenezene or hexebromobenzene.

Question: 11

What is the general pattern of reactivity of benzene towards electrophone?

Answer: 11

11-22

The highly stable delocalized electron of benzene ring not radley available for the nucleophilic attack like the electrons of alkenes.Therefore the electron of benzene ring do not assist in the attack of weal electrophiles,It means that more powerful electrophiles are required to penetrate and break the continuous sheath of electron cloud in benzene.

Question: 12

What is meant by the terms:i) Aromatic ii) Oxidation

Answer: 12

12-22

Aromatic:The term aromatic was derived from the Greek word aroma meaning fragrant and was used in organic chemistry for s special class of compounds.These compounds have low hydrogen to carbon ratio in their molecular formula and have a characteristic odour. These often produced by benzene or derivatives of benzene.

Question: 13

How benzene is converted into malic acid by catalytic oxidation?

Answer: 13

13-22

Benzene ring is determine when it is strongly heated with air in the presence of V₂O₅as a catalyst and maleic acid is obtained.

Question: 14

What happens when Acidified KMnO₄is added to Methyl Benzene and Ethylbenzene?

Answer: 14

14-22

Alkyl benzenes re readily oxidized by acidified KMnO_{4.In these reaction alkyl groups are oxidizedkeeping the benzenering intact.}

Question: 15

Write down nitration and sulphonation of benzene?

Answer: 15

15-22

The introduction of NO₂group in benzene ring is called Nitration,.The nitration of benzene takes place when it is heated with a 1:1 mixture of conc.HNO₃and conc.Sulphuric at 50-55 degree acid reacts with nitrir acid to generate nitronium ion.

Question: 16

Justify that Ethene is more reactive than C₆H_6.

Answer: 16

16-22

The highly sable ,delocalized electron of benzene ring not readily available for the nucleophilic attack like the electron of alkenes,therefore the electrons of benzune ring do not assist in the attack of weak electrophiles.

Question: 17

What is meant by directive influence of substituent?

Answer: 17

17-22

When an electrophile substitution reaction take place on the benzene ring,we get only one monosubstituted benzene all the six position in the ring are equivalent .However introduction of second group into the ring may give three isomeric distributed products ,ortho,meta and para.

Question: 18

Predict major product of bromination of nitrobenzene.

Answer: 18

18-22

m-bromonitrobenzene is the major product of bromination of nitrobenzene because nitro group on benzene is meta directing .

Question: 19

What is meant by directing group?

Answer: 19

19-22

The groups which withdraw the electrons of the benzene ring towards themselves and reduce the availability to the electrophiles are called meta directing groups.The result is the decrease chemical reactivity of benzene,In their presence incoming electrophiles will prefer to attack on meta position nrather than orho and para position.

Question: 20

Why hydroxyl group in ortho and para directing?

Answer: 20

20-22

Hydroxyl group release electron to the benzene ring .there by facilities the availability of electron to the electrophiles at ortho and para position.This result in the increase chemical reactivity of benzene ring towards electrophiles,The benzene ring can offer more than one position the new incoming group.

Question: 21

How will you prepare the following compound from benzene in two steps?m-chloronitrobenzene.

Answer: 21

21-22

The introduction of NO group in benzene ring is called Nitration,The nitration of benzene takes place when it is heated with a 1:1 mixture of concat 50-55 degree.

Question: 22

Define two reaction which confirm presence of three double bonds in benzene ring.

Answer: 22

22-22

1.Benzene is reduced to cyclohexane on heating at high temperature which hydrogen in the presence of Pt in an acidic solvent or Ni at 200 degree as a catalyst.

2.Benzene reacts with chlorine and bromine in the presence of sunlight to give addition products ,hexachlorobenzene or hexabromobenzene.

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12th Class Chapter 9 Chemistry Short Questions

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