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Organic Chemistry

Blazing goIITian

Joined:	2 Jan 2008
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4 Apr 2008 20:40:23 IST

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647

aldol

None

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

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rohit

Blazing goIITian

Joined: 24 Jan 2008

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4 Apr 2008 20:46:59 IST

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

hence they show cross aldol condensation

chemicaltester

Scorching goIITian

Joined: 12 Mar 2008

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4 Apr 2008 21:44:28 IST

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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

SHYAM

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Joined: 2 Apr 2008

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4 Apr 2008 23:00:34 IST

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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.

maga ishwarya

Cool goIITian

Joined: 24 Apr 2007

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6 Apr 2008 19:31:03 IST

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because there no alpha hydrogen in HCHO and C6H5CHO

varsha valli g.

Blazing goIITian

Joined: 31 Jan 2007

Posts: 515

6 Apr 2008 21:31:44 IST

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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.
!!!!!!!!!!!!!!!!!!!!

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