Question

The increasing order of the following compounds towards $\mathrm{HCN}$ addition is:

• A. $\left(\mathrm{iii}\right)<\left(\mathrm{i}\right)<\left(\mathrm{iv}\right)<\left(\mathrm{ii}\right)$
• B. $\left(\mathrm{iii}\right)<\left(\mathrm{iv}\right)<\left(\mathrm{i}\right)<\left(\mathrm{ii}\right)$
• C. $\left(\mathrm{i}\right)<\left(\mathrm{iii}\right)<\left(\mathrm{iv}\right)<\left(\mathrm{ii}\right)$
• D. $\left(\mathrm{iii}\right)<\left(\mathrm{iv}\right)<\left(\mathrm{ii}\right)<\left(\mathrm{i}\right)$

Answer 1

The correct option is A

$\left(\mathrm{iii}\right)<\left(\mathrm{i}\right)<\left(\mathrm{iv}\right)<\left(\mathrm{ii}\right)$

The correct options are (a)

The Explanation for the correct options:

(a)

• Explanation: sequence of increasing reactivity to HCN addition The reactivity in nucleophilic addition increases with group electrophilicity.
• Formaldehyde is most reactive towards the addition reaction of hydrogen cyanide to form the corresponding cyanohydrin.
• The reactivity in nucleophilic addition increases with group electrophilicitygreater.
• Diagram:

The Explanation for the incorrect options:

(b)

• Explanation: Intermolecular hydrogen bonds exist in all of the compounds listed.
• ${\mathrm{O}}_2\mathrm{N}$ has a lower concentration than ${\mathrm{H}}_3\mathrm{CO}$, and${\mathrm{H}}_3\mathrm{CO}$ has a lower concentration than${\mathrm{NO}}_2$.
• Because the$\mathrm{O}$is more electron negative than the${\mathrm{NO}}_2$in other compounds, it has the strongest hydrogen bonding.

(c)

• Explanation:
• ${\mathrm{OCH}}_3$ has a lower concentration than${\mathrm{O}}_2\mathrm{N}$,.
• Because this$\mathrm{O}$more electron negative than the$\mathrm{CHO}$in other compounds, it has the strongest hydrogen bonding.

(d)

• Explanation: All of the compounds listed have intermolecular hydrogen bonds.
• The density ${\mathrm{O}}_2\mathrm{N}$is lower than that of${\mathrm{NO}}_2$, and,${\mathrm{NO}}_2$the density of is lower than that of${\mathrm{H}}_3\mathrm{CO}$.
• $\mathrm{CHO}$has the strongest hydrogen bonding because the $\mathrm{O}$is more electron negative than the $\mathrm{NO}$ other compounds.

The correct option is (c): As a nucleophile, CN- attacks the -CHO group with the highest positive charge first. The -M and -I group boosts the (+ve) charge's strength. Consequently, the following is the order of reactivity