12th Class Chemistry Chapter 10 Short Questions with Answers Solved

Question: 1

Give general mechanism pattern of S_n2 reaction?

Answer: 1

1-25

In nucleophilic substitution bimolecular the reaction of attack of the attaching nucleophile is from the side which is opposite to the leaving group.In order to give the nucleophile enough room to attack the substrate carbons atom changes its state of hybridization from tetrahedral to planner sp².

Question: 2

What is Grignard reagent ?How it is prepared?

Answer: 2

2-25

R-Mg-X known as Grignard reagent ,These are derivatives of alkyl halided belonging to class of organo metallic compounds .Grignard reagent was first prepared by Victor Grignard in 1900. Grignard reagent is so important in organic synthesis that almost all the classes of organic compounds can be prepared from them,Due to their importance and organic compounds can be prepared from them.

Question: 3

What are primary and tertiary Alkyl Halides?

Answer: 3

3-25

In a primary alkyl halide halogen atom is attached with carbon which is further attached to one or more carbon atom.In a tertiary alkyl halide halogen atom is attached with a carbon which is further attached to three carbon atom.

Question: 4

Define Nucleophile.

Answer: 4

4-25

Nucleophile means nucleus loving ,It has an unshared electron paired available for bonding and in most cases it is basic in character,It may have negatively charged or neutral.

Question: 5

Give importance of Grignard reagents?

Answer: 5

5-25

Grignard reagents is so important in organic synthesis that almost almost all the classes of organic compound can be prepared from them.,Due to their importance and application Victor Grignared was awarded Nobel Prize in chemistry.

Question: 6

Write down the main factors on which reactivity of Alkyl halides depends.

Answer: 6

6-25

There are two main factors which govern the reactivity of R-X bond.

C-X bonds: Strength of bond in compound would be the most reactive one while fluro compound will be the least reactive.

C-X bond polarity:The greatest electronegativity difference between carbon and fluorine atoms in alkyl fluorides,If an electrophile is the attaching reagent then this difference suggest that alkyl fluorides would be the most reactive alkyl halides.

Question: 7

What are b-elimination reaction?

Answer: 7

7-25

When nucleophile attacks on hydrogen atom attached to the beta carbon of the alkyl halide,we get an alkene ,such type of reaction are called elimination reaction .In E1 mechanism the first step is the slow ionization of the substrate to give a carbocation.In the second step the nucleophile attacks on hydrogen to give an alkene as a product.

Question: 8

Why does SN₂mechanism give a product with inversion of configuration?

Answer: 8

8-25

In nucleophilic substitution bimolecular the direction of attack of the attaching nucleophile is from the side which is opposite to the leaving group .In order to give the the nucleophile enough room to attack ,the substrate carbon atom changes it state of hybridization from tetrahedral to planner sp².

Question: 9

Give reason for reactivity Grignard reagent?

Answer: 9

9-25

The reactivity of Grignard reagent is due to the nature of C-mg Bond which is highly polar,Magnesium is more electropositive than carbons and the C-mg bond though covalent is highly polar ,giving alkyl carbons the partial negative charge,This negative charge is unusual character which makes the alkyl group highly reactive towards electrophile center. Mostly reaction shown by Grignard reagent are exothermic.

Question: 10

Explain terms Leaving Group and Electrophile.

Answer: 10

10-25

Leaving group:leaving group is nucleophile which leave during substitution reaction of alkyl halide,It departs with an unshared pair of electron If we wish a S_nreaction to proceed in the forward direction the incoming nucleophile must be stronger than the departing one,CI,Br,I are goof nucleophile as well as a goof leaving group.

Electrophile: It is a specie which attracts electrons.The carbon atom of an alkyl group attaches with the halogen atom and bearing a partial positive charged is called an electrophile center,An electrophile may be neutral or positively charged.

Question: 11

What is the natural of C-mg bond in R-mg-X?

Answer: 11

11-25

The reactivity of Grignard reagent is due to the nature of C-mg bond which is highly polar, Magnesium is more electropositive than carbons and the C-mg bond though covalent is highly polar ,giving alkyl carbons the partial negative charge,This negative charge is unusual character which makes the alkyl group highly reactive towards electrophile center.

Question: 12

Why alkyl halides are more reactive than alkanes?

Answer: 12

12-25

An alkyl halides molecule consists of two parts,an alkyl group with a partial positive charge on the carbon atom attached to halogen atom and the halide atom with partial negative charge,While alkanes have no partial position or negative charged sites in their molecules.Halogens atom attached to alkyl groups is more electronegative which makes the alkyl and halide weak bonds.

Question: 13

What are elimination reaction?

Answer: 13

13-25

When nucleophile attacks on hydrogen atom attached to the b carbon of the alkyl halide,we get an alkene such type of reaction are called elimination reaction.

Question: 14

During S_n1 reaction,What is the significance of first step?

Answer: 14

14-25

The first step involved the breakage of a covalent bond so it is slow step as compared to the second step which involve the energetically favourable combination of ions,the first step is therefore called the rate determining step.The mechanism step is called unimolecular because only one molecule take part in the rate determining step.

Question: 15

Write down any two method for the preparation of Alkyl halides?

Answer: 15

15-25

1.Alchol may be converted to the corrosponding alkyl halide by the action of halogen acid in the presence of ZnCI₂ which acts as catslyst.

2.Alcholo reacts with th;onyl chloride in pyrindine as a solvent to give alkyl chlorides which escape leaving behind the pure product.

Question: 16

Write a note on R-Mg-X.

Answer: 16

16-25

R-Mg-X are known are Grignard reagent,These are derivatives of alkyl halides belonging to class of organo metallic compounds,Grignard reagent is so important in organic synthesis that almost all the classes of organic compounds can be prepared from them,Due to their importance and application Victor Grignard was awarded Noble Prize in Chemistry.

Question: 17

Why the reactivity of Alkyl halides depend upon Bind Energy.

Answer: 17

17-25

The strength of bond shows that iodo compound with the weakest bonds would be the most reactive one whlefluor compound will be the leat reactive i.e the order of reactivity of alkyl halid should be R-I>R-Br>R-CI>R-F

Question: 18

Give mechanism of E1 elimination reaction in two steps.

Answer: 18

18-25

.In E1 mechanism the first step is the slow ionization of the substrate to give a carbocation.In the second step the nucleophile attacks on hydrogen to give an alkene as a product.

Question: 19

How will you prepare Ethyl chloride using thionylchloride.

Answer: 19

19-25

Alcholos reacts with thinoyl chloride in pyridine as a solving to give alkyl chlorides This method is especially useful since the by production are gases which escape leaving behind the pure product.

Question: 20

Define Primary Alkyl Halides and secondary alkyl Halides.

Answer: 20

20-25

The alkyl halides in which halogen atom halogen atom is attached with carbon which is further atached to one or no carbon atom is called primary alkyl halide.

Secondry alkyl Halide:The alkyl halides in which halogen atom is attached with a carbon which is durther attached to two carbon atom is called secondry alkyl halide.

Question: 21

Reaction of ethyl bromide with OH nucleophile is S_n2 justify?

Answer: 21

21-25

In nucleophilic substitution bimolecular the direction of attack of OH^-,the attaching nucleophile is from the side which is opposite to the leaving group ,in order to give to the nucleophile enough room to attack on ethyl bromide the substrate carbon atom changes its state of hybridization from tetrahedral.

Question: 22

What is the role of stability of carbonium ion in deciding the Mechanism of substitution reaction.

Answer: 22

22-25

The first step involve the breakage of covalent bond so it is slow step as compared to the second step which involves the energetically favourable combination of ions.The first step is therefore called the rate determining step.The mechanism is called unimolecular because one molecule takes part in the rate determining step.

Question: 23

Discuss E2 mechanism.

Answer: 23

23-25

In E2 mechanism the nucleophile attacks and the leaving group leaves at the same time with formation of carbon carbon double bond.

Question: 24

Inversion of configuration is 50% in S_n1.Explain?

Answer: 24

24-25

In S_n1 mechanism the nucleophile attacks when the leaving group had already gone,carbocation is a planner specie allowing the nucleophile to attack on it from both the direction with equal ease,We therefore observe 50% inversion of configuration and 50% reternation of configuration.

Question: 25

Convert C₂H₅CI to T.E.L.

Answer: 25

25-25

Ethyl chloride react with sodium lead alloy giving tetraethyl lead ,This compound is important anti knock agent and used in gasoline.

C₂H₅CI + Na₄Pb ----(C₂H₅)₄PB + 4 NaCI

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12th Class Chapter 10 Chemistry Short Questions

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