Question

Which is the major organic product that results from the reaction of propanal with hydrogen cyanide HCN? A) B) CNCN CH CH" CH CH, D) CH,CH, C) HO CH,CH, CN CH HON CH2CH. CH

Answer 1

Option C is correct ans.

Oxygen is far more electronegative than carbon and so has a strong tendency to pull electrons in a carbon-oxygen bond towards itself. One of the two pairs of electrons that make up a carbon-oxygen double bond is even more easily pulled towards the oxygen. That makes the carbon-oxygen double bond very highly polar.

The cyanide ion comes from hydrogen cyanide, which is a covalent molecule. Hydrogen cyanide is very weakly acidic, which means that it can lose a hydrogen ion - although not very easily.

H:CEN loss of a hydrogen . CEN ion to give CN-

Notice that when the hydrogen is lost, it leaves its electron behind on the carbon. That leaves a lone pair of electrons on that carbon, together with a negative charge. It's essential to realise that in the cyanide ion the active lone pair and the charge are on the carbon atom and not the Nitrogen.  

Step1.

as the cyanide ion approaches the slightly positive carbon atom, the lone pair of electrons is attracted towards the carbon and forms a bond with it. At the same time the two electrons in one of the bonds joining the carbon to the oxygen are repelled until they end up entirely on the oxygen - giving it a negative charge.

Step 2.

The negative ion formed then picks up a hydrogen ion from somewhere - for example, from a hydrogen cyanide molecule.

Sep 1 - си - си, с — сня — СН3-С-н (2 Step 2 - ОН CH CH2 - с ч CH₃ - CH₂