(a) Write the chemical equation for the reaction involved in Cannizzaro reaction.
(b) Draw the structure of the semicarbazone of ethanal.
(c ) Why pKa of `F-CH_(2)`-COOH is lower than that of `Cl-CH_(2)-COOH`?
(d) Write the product in the following reaction :
`CH_(3) - CH = CH - CH_(2) CN underset((ii) H_(2)O)overset((i) DIBAl-H)rarr`
(e) How can you distinguish between propanal and propanone?

Explanation

(a) Aldlhyde which do not contain `alpha` - Hydrogen atom treated with conc. NaOH/KOH undergo self oxidation reduction.

(c ) Due to stronger `(-I)` effect, inductive effect of F over Cl, the `FCH_(2) COO^(-)` ion is much more stable than `ClCH_(2) COO^(-)` ion. Hence, `FCH_(2)COOH` is stronger acid than `ClCH_(2)COOH`. Hence, PKa value of `F-CH_(2)` COOH is lower than that of `Cl-CH_(2)COOH`.
(d) `CH_(3) - CH = CH - CH_(2) CN underset((ii)H_(2)O)overset((i) DIBAl-H)rarrCH_(3)CH=CHCH_(2)CHO`
(e) `underset("Propanal")(CH_(3)CH_(2))CHO and underset("Propanone")overset(O)overset(||)(CH_(3)C-CH_(3))["Iodo form test"]`
`CH_(3)CH_(2)CHO+NAOI rarr` no reaction as there is no methyl group attached to carbonyl group.
Whereas, `CH_(3)-overset(O)overset(||)(C)-CH_(3)+NaOIrarrCH_(3)-overset(O)overset(||)(C)-ONa+CHI_(3)("yellow ppt")`