2-chloro-2-methylpentane on reaction with sodium methoxide in methanol yields:

  • Both a and c

  • Only c

  • Both a and b

  • Both a and b


D.

Both a and b

Strong nucleophile  polar solvent (MeOH) gives elimination products Products over substitution products but all products are possible in different yields.

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 A compound 'A' of molecular formula C2H3OCl undergoes a series of reactions as shown below. Write the structures of A, B, C and D in the following reactions:

 

 

(b) Distinguish between the following:

(i) C6H5-COCH3 and C6H5 - CHO

(ii) Benzoic acid and methyl benzoate

(c) Write the structure of 2- methylbutanal.


(a) Using the given molecular formula, compound A is Ethanoyl Chloride CH3COCl, which undergoes reaction with poisoned palladium.
On carrying hydrogenation of A in the presence of poisoned palladium, we get an aldehyde. Hence, B can be Ethanal, CH3CHO.
An aldehyde, on treating with dilute alkali, undergoes aldol condensation reaction. Hence, C can be CH3CH (OH) CH2CHO.
On heating an aldol product, it loses water to produce a double bond and we get CH3CH=CHCHO.
Hence, we have

 

(b)
(i) Acetophenone has methyl group attached to carbonyl carbon while benzaldehyde does not. Therefore, we can use iodoform test to distinguish between the two. Acetophenone will undergo iodoform test and give a yellow precipitate.

C6H5-COCH3    C6H5COOH + CHI3

Acetophenone                           (yellow ppt.)

 

C6H5CHO    No reaction

Benzaldehyde

(ii) Benzoic acid can react with sodium bicarbonate to give brisk effervescence due to the release of CO2, while methyl benzoate does not.

C6H5COOH + NaHCO3----> C6H5COONa + H2O + CO2

Benzoic acid                                               (brisk effervescence)

 

C6H5COOCH3 + NaHCO3---> No reaction

Methyl benzoate

 

(c) The Structure of 2- methylbutanal is:

 

 

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How will you bring about the following conversions?

 (i) Propanone to propane

(ii) Benzoyl chloride to benzaldehyde

(iii) Ethanal to but-2-enal


 (i) Conversion of Propanone to Propane:


 (ii) Conversion of Benzoyl chloride to benzaldehyde:

(iii) On treatment with dilute alkali, ethanol produces 3-hydroxybutanal gives But-2-enal on hheating.

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Give chemical tests to distinguish between 

(i) Propanal and propanone, 

(ii) Benzaldehyde and acetophenone. 

(b) How would you obtain 

(i) But-2-enal from ethanal, 

(ii) Butanoic acid from butanol, 

(iii) Benzoic acid from ethylbenzene? 


(i) Propanal (CH3CH2CHO) can be distinguished from propanone (CH3COCH3) by iodoform test. 

Being a methyl ketone, propanone on treatment with I2/NaOHundergoes iodoform reaction to give a yellow ppt. of iodoform 

 
(ii) Benzaldehyde (C6H5CHO) and acetophenone (C6H5COCH3) can be distinguished by iodoform test. 

 

Acetophenone, being a methyl ketone on treatment with I2 /NaOH undergoes iodoform reaction to give a yellow ppt. of iodoform. On the other hand, benzaldehyde does not give this test. 

 b)
i) 



ii) 


iii)

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(a) Describe the following giving linked chemical equations: 

 (i) Cannizzaro reaction 

 (ii) Decarboxylation 

(b) Complete the following chemical equations: 

 


(i) Cannizaro reaction 

In this reaction, the aldehydes which do not have a -hydrogen atom, undergo self-oxidation and reduction (disproportionation) reaction on treatment with a concentrated alkali. 
Example: 

 

(ii) Decarboxylation 

The decarboxylation reaction can be carried out either by using soda lime or by electrolysis 

Using soda lime: Sodium salts of carboxylic acids when heated with soda lime (NaOH + CaO) in the ratio 3:1)  undergo decarboxylation reaction to yield alkanes. 

 

Electrolytic decarboxylation: Electrolysis of aqueous solutions of sodium or potassium salts of carboxylic acids give alkanes having twice the number of carbon atoms present in the alkyl group of acid. 

 This is known as Kolbe’s decarboxylation. 

 2RCOONa--> 2RCOO- + 2Na+

 H2O-->2OH- + 2H+

 
At Anode:-

2RCOO- - 2e---> CO2 + R - R

At Cathode:-

 2H+ + 2e----> H2


b) 

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