IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

bhartibhanushali

formaldehyde and benzaldehyde do not show aldol condnsation due to lack of alpha hydrogen
then why do they show cross aldol condenstion

also it is given in my book formaldehyde undergoes series of aldol condensation to form sugar .please explain this

dream

the need for cross aldol conddensation is that atleast one of the reactant must have alpha hydrogen

hence they show cross aldol condensation

chemicaltester

i dunno know why but that does happen

formaldehyde and benzeldehyde both which do naot have alpha hydrogen undergoes series to form 3 phenyl pro2enal

(C6H5)CHO + CH3CHo = (C6H5) CH(OH) -CH2-CHO = (C6H5)-CH=CH-CHO

the reason might some reasonance and all that

also formaldehyde IN PRESENCE OF DILUTE ALKALI forms fromose

i think the proton of water attaches with oxygen

Agni2

The imp step in aldol condensation is the formation of carbanion. carbanion is formed only if there is a

-hydrogen. In acataldehyde we've alpha hydrogen hence it forms carbanion which then reacts with benzaldehyde to give you the product.

magaishwarya

because there no alpha hydrogen in HCHO and C6H5CHO

varshavallig

aldol condensation requires only the 2nd aldehyde to have an alpha H not necessarily the 1st also.so HCHO and benzaldehyde can b used as the 1st aldehyde in cross aldol condensation,only thing is that they cannot form their self products.
!!!!!!!!!!!!!!!!!!!!

Ask & Discuss Questions with Community & Experts