Formaldehyde reacts with $ HCN $ ($ NaCN + HCl $) to give a compound: · Aldehydes & Ketones MDCAT Past Paper MCQ

Chemistry Aldehydes & Ketones MDCAT 2012

PMDC Verified Question 89 of 94

Formaldehyde reacts with $ HCN $ ($ NaCN + HCl $) to give a compound:

$ CH_3-CH(OH)CN $

$ CH_3-CO-CN $

$ H_2C(OH)CN $

$ H_2C(CN)_2 $

Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:

Option C: $ H_2C(OH)CN $

Concept:

Aldehydes react with hydrogen cyanide ($ HCN $) in a nucleophilic addition reaction to form cyanohydrins.

Formula:

$$ H_2C=O + HCN \longrightarrow H_2C(OH)(CN) $$

Solution:

Formaldehyde ($ HCHO $) has a central carbonyl carbon bonded to two hydrogen atoms.

The cyanide nucleophile ($ CN^- $) attacks the carbonyl carbon, and the oxygen gets protonated.

The resulting product has both an $ -OH $ group and a $ -CN $ group attached to the same $ CH_2 $ carbon, making it formaldehyde cyanohydrin ($ H_2C(OH)CN $).

Why other options are incorrect:

Option A is the cyanohydrin of acetaldehyde. Option B is an acyl cyanide. Option D is a dinitrile, which cannot form via this simple addition.

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