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Q 12.20     Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why?

In carboxylate ion the electron is delocalised between oxygen, which is electronegative in nature. But in case of phenoxide ion, the electron are delocalise between less electronegative atom and also phenoxide ion has non-equivalent resonance structure. Therefore, carboxylate ion is more resonance stable than phenoxide ion and we know that more stable the conjugate base of an acid,  high strong...

Q 12.19     An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollens’ reagent but forms an addition compound with sodium hydrogen sulphite and give a positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible structure of the compound.

In the question, it is given that, % of carbon = 69.77 % of Hydrogen = 11.63 % of Oxygen = (100-69.77-11.63) = 18.6 Now, the no. of moles of the components are- Thus ration of C:H:O = 5.81:11.63:1.16 To get empirical formula we need to divide them by 1.16 .So, C:H:O= 5:10:1 So, the empirical formula is  The molecular mass of the compound =  Since the compound does not give tollens...

Q 12.18     Give plausible explanation for each of the following:

        (iii)     During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed.

If either water or the ester is not removed immediately then ester can react with water and again and give back the reactants. Thus to shift the reaction in forward direction we need to produce more ester or remove either of the two. 

Q 12.18     Give plausible explanation for each of the following:

         (ii)     There are two –NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones. 

In Semicarbazide, One of the  group is involved in resonance with the carbonyl group, which is directly attached. Therefore, it cannot act as a nucleophile (its electrons are less available or less electron density at that group). But the other  group is not participating in resonance, so it can act as nucleophile and attack on the carbonyl carbon of ketone and aldehyde.

Q 12.18     Give plausible explanation for each of the following:

          (i)     Cyclohexanone forms cyanohydrin in good yield but 2,2,6-trimethylcyclohexanone does not. 

Structure of 2,2,6-trimethylcyclo hexanone Cyclohexanone forms cyanohydrin when the nucleophile () attack on cyclohexanone. In this case, there is less hindrance around the CO group so the nucleophile can attack easily. But in case of 2,2,6-trimethylcyclo hexanone at the alpha () position, there is a hindrance because of the methyl groups. Thus the nucleophile cannot attack effectively.

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

        (xi)      \xrightarrow[ii. Zn - H_{2}O]{i. O_{3}} 

The above reaction is ozonolysis reaction in which ozone molecule breaks the double bond of the alkene and formed a ketone or aldehyde as a product.

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

        (x)     

Diborane reacts with alkene to give trialkyl boranes (addition product) and this is oxidised to alcohol by using hydrogen peroxide. After then pyridinium chlorochromate (PCC) is reacts with alcohol to convert it into Aldehyde group.


reacts 
 

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Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

         (ix)     \overset{CrO_{2}}{\rightarrow}

oxidises the OH(alcohol) group into keto-group (-CO) and finally the product produced is cyclohexanone

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

      (viii)      CH_{2}COCH_{2}COOC_{2}H_{5}\xrightarrow[ii. H^{+}]{i. NaBH_{4}}  

In this reaction  is a reducing agent, which reduces the CO group of the compound.      

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

        (vii)      C_{6}H_{3}CHO + CH_{3}CH_{2}CHO \xrightarrow[\Delta ]{dil NaOH}

The given eaction is cross aldol reaction between benzaldehyde and propanal in presence of dil. sodium hydroxide

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

         (vi)     \overset{NaCN / HCl}{\rightarrow}

In this reaction, the nucleophile CN attacks on -CHO group because it has more reactivity towards . So the reaction gives

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

         (v)      \overset{\left [ Ag\left ( NH_{3} \right )_{2} \right ]^{+}}{\rightarrow}  

SInce, the give reactant is a aldehyde compound, So it give positive tollen's test by reducing the tollens reagent.

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

          (iv)     

Benzene reacts with benzoyl chloride in presence of anhydrous aluminium chloride () to give benzophenone and also HCl as a by-product.

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products

        (iii)      C_{6}H_{5}CHO\overset{H_{2}NCONHNH_{2}}{\rightarrow}

In this reaction, the  group which not directly attached with the carbonyl group act as a nucleophile and attack on -CO group of benzaldehyde and water molecule is also produced as a by-product. So, the final product is-

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

         (ii)        \xrightarrow[heat]{SoCl_{2}}

The -OH groups of both carboxylic acid is replaced by the chlorine  So, the overall reaction is

Q 12.17     Complete each synthesis by giving missing starting material, reagent or products.

          (i)      \xrightarrow[KOH, heat ]{KMnO_{4}}

Potassium permanganate oxidise the substituted ethyl group to group and due to presence of KOH, formed carboxylic acid salts (potassium benzoate)

Q 12.16     Describe the following.

        (iv)     Decarboxylation

Decarboxylation- The reaction in which the carboxylic acid loses carbon dioxide to hydrocarbon, in the presence of sodalime( and in the ratio of 3:1). This reaction is known as decarboxylation.

Q 12.16     Describe the following.

        (iii)     Cross aldol condensation 

Cross aldol condensation- In aldol condensation, if the reactants are two different aldehyde or ketone, then it is called cross-aldol condensation. If both of the reactants contains alpha-hydrogen atoms then it gives a mixture of four products. If the reactants contain alpha-hydrogen atoms then,  

Q 12.15     Describe the following.

        (ii)      Cannizzaro reaction 

Cannizzaro reaction- Aldehyde which do not have any alpha- hydrogen, undergo self oxidation as well as reduction reaction on treating with concentrated alkalies. In this reaction, one molecule gets reduced and other is oxidised to carboxylic acid salt.

Q 12.16     Describe the following.

         (i)      Acetylation 

Acetylation- The addition of acetyl functional group () in an organic compound is called acetylation. Acetic anhydride() and acetyl chloride              () are mostly used as acetylating agents. This reaction is happens in presence of a base such as pyridine etc.
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