Recent questions tagged ketons

Description : Explain why o-hydroxybenzaldehyde is a liquid at room temperature while p-hydroxybenzaldehyde is a high melting solid.

Last Answer : Due to interamolecular H-bonding ortho-hydroxy benzaldehyde exists as discrete molecule whereas due to intermolecular H-bonding, p-hydroxybenzaldehyde exists as associated molecules. To break these intermolecular ... a liquid at room temperature while p-hydroxy benzaldehyde is a high melting solid. 

Description : Arrange the following carboxyl compounds in increasing order of their reactivity in nucleophilic addition reactions. Explain with proper reasoning : Benzaldehyde. p-tolualdeyde, p-nitrobenzaldehyde, Acetophenone.

Last Answer : Ans. Acetophenone is a ketone while all others are aldehydes, therefore it is least reactive. In p-tolualdehyde, there is methyl group (CH3 ) at para position w.r.t. to the ... overall order of increasing reactivity : acetophenone < p-tolualdehyde < benzaldehyde < p-nitrobenzaldehyde. 

Description : Why does solubility decreases with increasing molecular mass in carboxylic acid ?

Last Answer : Ans. Because of increase in alkyl chain length which is hydrophobic in nature. 

Description : Why does methanal undergoes Cannizaro’s rxn ?

Last Answer : Ans. Because it does not possesses hydrogen atom. Only those aldehydes can undergo  Cannizaro reaction which do not possess hydrogen atoms.

Description : Why does methanal not give aldol condensation while ethanol gives ? 

Last Answer : Ans. This is because only those compounds which have hydrogen atoms can undergo  aldol reaction. Ethanol possesses -hydrogen and undergoes aldol condensation.   Methanal has no hydrogen atoms, hence does not undergo aldol condensation. 

Description : What are Hemiacetal and acetal ? 

Last Answer : Ans. Hemiacetal and acetals are formed by addition of alcohols on carboxyl compounds.  

Description : Would you expect benzaldehyde to be more reactive or less reactive in nucleophlic addition reaction than propanal ? Explain.

Last Answer : C-atom of carbonyl group of benzaldehyde is less electrophilic than C-atom of carbonyl group in propanal. Polarity of carbonyl group is in benzaldehyde reduced due to resonance making it less ... group in it is more than in benzaldehyde. This makes propanal more reactive than benzaldehyde. 

Description : Why pcc cannot oxidise methanol to methane and while KMnO4 can ?

Last Answer : This is because pcc is a mild oxidising agent and can oxide methanol to methanal only. While KMnO4 being strong oxidising agent oxidises it to methanoic acid. 

Description : Give the composition of Fehling A and Fehling B ?

Last Answer : Ans. Fehling A = aq. CuSO4 Fehling B = alkaline sodium potassium tartarate (Rochelle Salt)

Description : Why are aldehydes more reactive than ketones ? 

Last Answer : Ans. It is because of 2 reasons : The carboxyl compounds (both aldehydes & ketones) undergo nucleophilic addition reaction. (i) + I effect : The alkyl group in ketones due to their e- ... its reactivity. (ii) Steric hindrance : Due to steric hindrance in ketones, they are less reactive.

Description : Distinguish between : (i) Acetaldehyde and acetone (ii) Methanoic acid and Ethanoic acid.

Last Answer : (i) Acetaldehyde will give positive tests with Tollen’s reagent and Fehling Solns. whereas acetone will not give these test. (ii) Methanoic acid gives Tollen’s reagent test whereas ethanoic acid does not due to difference in their boiling points.

Description : Arrange the following compounds in increasing order of their acid strength. Benzoic acid, 4-Nitrobenzoic acid, 3, 4-dinitrobenzoic acid, 4-methoxy benzoic acid.

Last Answer : Since electron donating gps. decrease the acid strength therefore 4-methoxybenzoic acid is a weaker acid because methoxy sp. is E. D. G. than benzoic acid. Further since electron withdrawing gps. increase ... : 4-methoxybenzoic acid < benzoic acid < 4-nitrobenzoic acid < 3, 4, dinitrobenzoic acid.

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

Last Answer : Ans. The formation of esters from a carboxylic acid and an alcohol in the presence of acid catalyst in a reversible reaction. To shift the equilibrium in the forward direction, the water or ester formed should be removed as fast as it is formed.

Description : Why HCOOH does not give HVZ (Hell Volhand Zelinsky) reaction but CH3COOH does ?

Last Answer : Ans. CH3 COOH contains hydrogens and hence give HVZ reaction but HCOOH does  not contain -hydrogen and hence does not give HVZ reaction. 

Description : What makes acetic acid a stronger acid than phenol ?

Last Answer : Ans. Greater resonance stabilization of acetate ion over phenoxide ion. 

Description : What type of aldehydes undergo Cannizaro reaction ?

Last Answer : Ans. Aromatic and aliphatic aldehydes which do not contain hydrogens. 

Description : Suggest a reason for the large difference in the boiling points of butanol and butanal, although they have same solubility in water.

Last Answer : The b. pt. of butanol is higher than that of butanal because butanol has strong intermolecular H-bonding while butanal has weak dipole-dipole interaction. However both of them form H-bonds with water and hence are soluble.