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प्रश्न
What is meant by the following term? Give an example of the reaction in the following case.
Hemiacetal
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उत्तर
Gem-alkoxyalcohols are called hemiacetals. These are produced when a molecule of monohydric alcohol combines with an aldehyde in the presence of dry HCl gas.
\[\begin{array}{cc}
\ce{H3C}\phantom{.........................}\ce{CH3}\phantom{....}\ce{OH}\\
\backslash\phantom{...........................}\backslash\phantom{...}/\\
\ce{C = O + H - OCH3 <=>[Dry HCl_{(g)}] C}\\
/\phantom{...........................}/\phantom{...}\backslash\\
\phantom{....}\ce{H}\phantom{...........................}\ce{\underset{Hemiacetal}{H\phantom{....}OCH3}}\
\end{array}\]
APPEARS IN
संबंधित प्रश्न
Predict the products of the following reactions:
Write the products formed when CH3CHO reacts with the following reagents : HCN
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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) |  |
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