Correct order of decreasing reactivity towards nucleophilic addition reaction is:

A. Acetone

B. Formaldehyde

C. Acetaldehyde

D. Acetophenone

E. Benzophenone

Choose the correct answer from the options given below:

B > C > A > D > E

The correct answer is option 4. B > C > A > D > E.

Let us break down the reasoning behind the reactivity order of the carbonyl compounds towards nucleophilic addition reactions in more detail:

Reactivity of Carbonyl Compounds:

The reactivity of carbonyl compounds towards nucleophilic addition reactions is primarily influenced by two factors:

Electronic Effects: The nature of the substituents attached to the carbonyl carbon can either increase or decrease the partial positive charge on the carbonyl carbon, affecting its electrophilicity

Electron-withdrawing groups increase the electrophilicity of the carbonyl carbon, making it more reactive towards nucleophiles. Electron-donating groups decrease the electrophilicity of the carbonyl carbon, making it less reactive.

Steric Hindrance: The size of the groups attached to the carbonyl carbon can hinder the approach of nucleophiles.

Smaller groups cause less steric hindrance, leading to higher reactivity. Larger groups cause more steric hindrance, leading to lower reactivity.

Analysis of Each Compound:

B. Formaldehyde (HCHO):

Substituents: No alkyl or aryl groups attached; only hydrogen atoms are present.

Electronic Effect: No electron-donating or withdrawing groups.

Steric Hindrance: Minimal steric hindrance due to small hydrogen atoms.

Reactivity: Highest reactivity because the carbonyl carbon is highly electrophilic and easily accessible by nucleophiles.

C. Acetaldehyde (CH₃CHO):

Substituents: One methyl group (\(CH₃\)) attached.

Electronic Effect: The methyl group is slightly electron-donating, which slightly decreases the positive charge on the carbonyl carbon.

Steric Hindrance: Slightly more steric hindrance than formaldehyde due to the presence of the methyl group.

Reactivity: Less reactive than formaldehyde, but still relatively high reactivity due to minimal steric hindrance and only slight electron donation.

A. Acetone (CH₃COCH₃):

Substituents: Two methyl groups (\(CH₃\)) attached.

Electronic Effect: Both methyl groups are electron-donating, reducing the electrophilicity of the carbonyl carbon more than in acetaldehyde.

Steric Hindrance: Increased steric hindrance due to two methyl groups.

Reactivity: Less reactive than acetaldehyde due to greater electron donation and increased steric hindrance.

D. Acetophenone (C₆H₅COCH₃):

Substituents: One phenyl group (\(C₆H₅\)) and one methyl group (\(CH₃\)) attached.

Electronic Effect: The phenyl group has an electron-withdrawing effect through resonance, which would generally increase reactivity. However, it also has an electron-donating effect through induction, which can reduce reactivity.

Steric Hindrance: Significant steric hindrance due to the bulky phenyl group.

Reactivity: Less reactive than acetone because of the increased steric hindrance and the competing electronic effects of the phenyl group.

E. Benzophenone (C₆H₅COC₆H₅):

Substituents: Two phenyl groups (\(C₆H₅\)) attached.

Electronic Effect: The phenyl groups are electron-withdrawing by resonance but electron-donating by induction, leading to a reduced positive charge on the carbonyl carbon.

Steric Hindrance: High steric hindrance due to the presence of two bulky phenyl groups.

Reactivity: Least reactive because of the strong steric hindrance and the electron-donating effect through induction.

Final Order: Formaldehyde (B) > Acetaldehyde (C) > Acetone (A) > Acetophenone (D) > Benzophenone (E)

This order reflects the decreasing reactivity towards nucleophilic addition reactions, where formaldehyde is the most reactive and benzophenone is the least reactive.