Q.What happens when -

NH2-NHCONH2 is semicarbazide, a hydrazine derivative widely used to form solid, characterisable semicarbazone derivatives of aldehydes and ketones.

The structure NH2-NH-CO-NH2 consists of a hydrazine unit (H2N-NH-) attached to a urea-like carbonyl (-CO-NH2); this compound is called semicarbazide. …

Formaldehyde reacts with ammonia to form hexamethylenetetramine (urotropine).

6 HCHO + 4 NH3 -> (CH2)6N4 + 6 H2O

The product, hexamethylenetetramine (also called urotropine), is a cage-like compound used as a urinary antiseptic and in the manufacture of the explosive RDX.

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An oxime forms when a ketone's C=O reacts with hydroxylamine (NH₂OH) to give C=N–OH. Cyclopropanone oxime is this applied to the three-membered ring ketone cyclopropanone.

Cyclopropanone is the smallest cyclic ketone: a three-membered carbocyclic ring, $(CH_2)_2C=O$, i.e. two –CH₂– groups and one carbonyl carbon closing the ring.

An oxime is formed by the condensation of a ketone (or aldehyde) with hydroxylamine, with loss of water:

$R_2C=O + H_2N-OH \rightarrow R_2C=N-OH + H_2O$

Applying this to cyclopropanone: the ring carbonyl carbon's C=O is converted to C=N–OH, while the ring itself (the two –CH₂– groups completing the three-membered ring) is retained.

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Urotropine (hexamethylenetetramine) is the cage-like condensation product of formaldehyde and ammonia, formula (CH2)6N4.

Urotropine, also called hexamethylenetetramine or methenamine, is formed by the condensation of six molecules of formaldehyde (an aldehyde) with four molecules of ammonia:

$6HCHO + 4NH_3 \rightarrow (CH_2)_6N_4 + 6H_2O$

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