Give plausible explanation for each of the following:

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

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

(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.

1. Cyclohexanone forms cyanohydrin in good yield because the ketonic group has very less steric hindrance at both the ortho position but 2,2,6 tri methyl cyclohexanone have high steric hindrance which reduces the attack from CN nucleophile.

2. Only one Amino group is involved in the resonance structure of semicarbazide hence e^- density on NH₂ group decreases & it can't act as a nucleophile. But another NH₂ group can attack as a nucleophile to form semicarbazones.

3. It is the reversible reaction hence if we don't remove the water or ester the reaction may proceed in backward direction, for that It is essential the water or

...more

1. Cyclohexanone forms cyanohydrin in good yield because the ketonic group has very less steric hindrance at both the ortho position but 2,2,6 tri methyl cyclohexanone have high steric hindrance which reduces the attack from CN nucleophile.

2. Only one Amino group is involved in the resonance structure of semicarbazide hence e^- density on NH₂ group decreases & it can't act as a nucleophile. But another NH₂ group can attack as a nucleophile to form semicarbazones.

3. It is the reversible reaction hence if we don't remove the water or ester the reaction may proceed in backward direction, for that It is essential the water or ester as soon as formed

 

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<p><strong>1. </strong>Cyclohexanone forms cyanohydrin in good yield because the ketonic group has very less steric hindrance at both the ortho position but 2,2,6 tri methyl cyclohexanone have high steric hindrance which reduces the attack from CN nucleophile.</p><div class="photo-widget-full"><div class="figure"><picture><source srcset="" media=" (max-width: 500px)"><img src="https://images.shiksha.com/mediadata/images/1749809636phpn8n0lo.jpeg" alt="" width="290" height="237" loading="lazy"></picture></div><div class="figure"><picture>2. Only one Amino group is involved in the resonance structure of semicarbazide hence e</picture>^-<picture>&nbsp;density on NH</picture>₂<picture>&nbsp;group decreases &amp; it can't act as a nucleophile. But another NH</picture>₂<picture>&nbsp;group can attack as a nucleophile to form semicarbazones.</picture></div></div><div class="photo-widget-full"><div class="figure"><picture><source srcset="" media=" (max-width: 500px)"><img src="https://images.shiksha.com/mediadata/images/1749809682php3QE72b.jpeg" alt="" width="690" height="109" loading="lazy"></picture></div><div class="figure"><strong>3. </strong>It is the reversible reaction hence if we don't remove the water or ester the reaction may proceed in backward direction, for that It is essential the water or ester as soon as formed</div></div><div class="photo-widget-full"><div class="figure"><picture><source srcset="" media=" (max-width: 500px)"><img src="https://images.shiksha.com/mediadata/images/1749809728phpwP7Och.jpeg" alt="" width="487" height="82" loading="lazy"></picture></div></div><p>&nbsp;</p>

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