Among the following compounds, which will react with acetone to give a product containing \(>\mathrm{C}=\mathrm{N}-?\) 1\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) 2\. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) 3\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHC}_{6} \mathrm{H}_{5}\) 4\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHNH}_{2}\) (a) 3,4 (b) \(1,3,4\) (c) 1,3 (d) 1,4

The process of creating a Schiff base involves the reaction between a primary amine and a carbonyl compound. This type of reaction is significant in organic chemistry because it facilitates the formation of a double bond between carbon and nitrogen, denoted as >C=N-. The reaction proceeds through a nucleophilic addition of the primary amine to the carbonyl carbon, followed by the elimination of water to form the imine or Schiff base. This reaction is strategically important in the synthesis of various organic compounds and in certain biochemical processes such as enzyme reactions.
For instance, aniline (C6H5NH2) when reacted with a carbonyl compound, such as acetone, yields a Schiff base as a result of its primary amine group. Schiff bases often feature prominently in the design of pharmaceuticals, dyes, and polymers because of their versatile reactivity and structural properties.

The reactivity of primary amines in organic chemistry is a pivotal concept to grasp. Molecules that contain a primary amine group, designated by the NH2 attached to an organic moiety, are particularly reactive towards carbonyl compounds. The nitrogen atom in a primary amine is nucleophilic, meaning it donates a pair of electrons to form a new chemical bond.
During the reaction with a carbonyl compound, the nucleophilic nitrogen of the primary amine initiates the process by attacking the electrophilic carbonyl carbon. After the formation of a carbinolamine intermediate, a molecule of water is removed, leading to the creation of an imine. This characteristic reactivity underlies the fundamental role that primary amines play in synthesizing imines and several other functional groups in organic synthesis.

Carbonyl compounds, characterized by the presence of a carbon-oxygen double bond, are highly reactive and participate in a plethora of chemical reactions. One of the most common reactions is with primary amines to form imines, as seen in Schiff base formation. The carbonyl carbon is electrophilic due to the polarity of the carbon-oxygen double bond, which makes it a prime target for nucleophilic attack by compounds such as primary amines.
Apart from imine formation, carbonyl compounds undergo various other reactions such as aldol condensations, acetal formation, and reductions to form alcohols. These reactions are fundamental to organic chemistry and are used extensively in the synthesis of complex organic molecules in medicinal chemistry and materials science.

Phenylhydrazine (C6H5NHNH2) is an organic compound with a primary amine group within its hydrazine segment. It exhibits remarkable reactivity with carbonyl compounds, akin to the behavior of primary amines. Phenylhydrazine reacts with carbonyl compounds to yield hydrazones, which feature a >C=N-N group. This reaction is akin to the formation of imines but involves nitrogen-nitrogen bond formation in addition to the carbon-nitrogen double bond.
Hydrazones are noteworthy intermediates in organic synthesis and can be used as precursors to other functional groups through further chemical transformations. Phenylhydrazine's reactivity aligns it with valuable reagents in the preparation of pharmaceuticals, agrochemicals, and many other nitrogen-containing organic compounds.