First slide
Cannizaro reaction
Question

Which of the following molecule gives positive 2,4-DNP test, positive Tollen's test, negative Fehling's test, negative Iodoform test and also can undergo Cannizzaro reaction

Moderate
Solution

HCHO…….no α-hydrogen……undergoes Cannizzaro reaction……cannot undergo aldol condensation…positive 2,4-DNP test….positive Tollen's test……..positive Fehling's test…….negative Iodoform test ;

CH3CHO…….contains α-hydrogen……cannot undergo Cannizzaro reaction…. undergoes aldol condensation…positive 2,4-DNP test….positive Tollen's test……positive Fehling's test…….positive Iodoform test ;

CH3-CO-CH3…….contains α-hydrogen……cannot undergo Cannizzaro reaction…. undergoes aldol condensation…positive 2,4-DNP test….negative Tollen's test……negative Fehling's test…….positive Iodoform test ;

C6H5-CHO…….no α-hydrogen……undergoes Cannizzaro reaction……cannot undergo aldol condensation…positive 2,4-DNP test….positive Tollen's test……..negative Fehling's test…….negative Iodoform test ;

Aromatic aldehydes are less reactive than aliphatic aldehydes……cannot reduce Fehling's and Benedict’s test ;

Aldehydes and Ketones containing -COCH3 group give yellow crystals of CHI3(positive haloform test) with Alkali (NaOH, KOH, Ca(OH)2, Na2CO3)+Halogen(X2…generally iodine)  (or) NaOX, CaOCl2;

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