Advertisements
Advertisements
Question
Give plausible explanation for the following:
There are two −NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.
Advertisements
Solution
Semicarbazide only has one of the two −NH2 groups resonance and this group is directly attached to the carbonyl-carbon atom.
Therefore, the electron density on −NH2 group involved in the resonance also decreases. As a result, it cannot act as a nucleophile. Since the other −NH2 group is not involved in resonance, it can act as a nucleophile and attack carbonyl-carbon atoms of aldehydes and ketones to produce semicarbazones.
APPEARS IN
RELATED QUESTIONS
How are the following compounds prepared?
benzaldehyde from benzene
Write the products formed when CH3CHO reacts with the following reagents : H2N – OH
Predict the product of the following reaction:
Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN)
Explain the mechanism of alkaline hydrolysis of tert-butyl bromide with energy profile diagram.
Write balanced chemical equations for action of ammonia on - acetaldehyde
Write balanced chemical equations for action of ammonia on - acetone
Acetone, Acetaldehyde, Benzaldehyde, Acetophenone – reactivity towards addition of HCN.
Which of the following has the most acidic hydrogen?
Which among the following is most reactive to give nucleophilic addition?
Arrange the following in the increasing order of their property indicated:
Ethanal, Propanone, Propanal, Butanone (reactivity towards nucleophilic addition)
What happens when ethanal is treated with excess ethanol and acid?
The product of following reaction is
\[\ce{CH3 - CH = CH - CH2 - CHO ->[i) LiAlH4][ii) H3O+]}\] ______?
The following questions are case-based questions. Read the passage carefully and answer the questions that follow:
| The carbon-oxygen double bond is polarised in aldehydes and ketones due to higher electronegativity of oxygen relative to carbon. Therefore, they undergo nucleophilic addition reactions with a number of nucleophiles such as HCN, NaHSO3, alcohols, ammonia derivatives and Grignard reagents. Aldehydes are easily oxidised by mild oxidising agents as compared to ketones. The carbonyl group of carboxylic acid does not give reactions of aldehydes and ketones. Carboxylic acids are considerably more acidic than alcohols and most of simple phenols. |
Answer the following:
(a) Write the name of the product when an aldehyde reacts with excess alcohol in the presence of dry HCl. (1)
(b) Why carboxylic acid is a stronger acid than phenol? (1)
(c) (i) Arrange the following compounds in increasing order of their reactivity towards CH3MgBr: (1)
CH3CHO, \[\begin{array}{cc}
\ce{(CH3)3C-C-CH3}\\
\phantom{....}||\\
\phantom{....}\ce{O}
\end{array}\], \[\begin{array}{cc}
\ce{CH3-C-CH3}\\
||\\
\ce{O}
\end{array}\]
(ii) Write a chemical test to distinguish between propanal and propanone. (1)
OR
(c) Write the main product in the following: (2)
| (i) |  |
| (ii) |  |
Aldehydes and ketones react with hydroxylamine to form ______.
Draw structures of the given derivatives.
The ethylene ketal of hexan-3-one
Draw structures of the given derivatives.
The ethylene ketal of hexan-3-one
Give an example of the reaction in the following case.
Imine
The major product of the following reaction is:
