The reagent which is used for the conversion of allyl alcohol into propenal is ${\mathrm{C}}_5{\mathrm{H}}_5{\mathrm{NH}}^{+}{\mathrm{CrO}}_3{\mathrm{Cl}}^{-}$ [$\mathrm{PCC}$ (pyridinium chlorochromate)].

$\underset{\mathrm{Allyl} \mathrm{alcohol}}{{\mathrm{CH}}_2=\mathrm{CH}-{\mathrm{CH}}_2-\mathrm{OH}}\stackrel{\mathrm{PCC}}{\to }\underset{\mathrm{Propenal}}{{\mathrm{CH}}_2=\mathrm{CH}-\mathrm{CHO}}$

Here, the reagent used should convert $-{\mathrm{CH}}_2-\mathrm{OH}$ into $-\mathrm{CHO}$ (oxidation) without affecting the double bonds.

$\mathrm{PCC}$: