difference between hemiactal/hemiketal formation and aldol reaction

[mindblowing]

can someone explain difference between hemiactal/hemiketal formation and aldol reaction ...in both cases starting material is alchol and aldehyde/ketone?

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[TexasDent]

I might be wrong but I don't think the aldol reaction forms hemiketals or hemiacetals; it is the aldehyde/ketone protecting reaction that does. Anyways looking at this sequence here: C-O-C-O-C is a ketal or acetal because the last carbon is there, here: C-O-C-O-H is a hemi ketal/acetyl because the element after the second O is an H. Now you look at the second C: C-O-C-O-C to see if it is a ketal or acetal. If this C has two C's coming off it is a ketal, if it only has one C coming off it is an acetal. This has to do with the protecting of an aldehyde or ketone reaction by reacting the ald/ket with 2 equivalents of an alcohol.

I hope this helps, I attached a picture for a visual aid to go along with the explanation.

 

[mindblowing]

i understand that aldol do not form hemiactal and hemiketal.. they are two different reaction... my question is that in both reaction(#1aldol and #2hemiketal formation)...reactant are same alchol and aldehyde so how should i know which one is which???

 

[TexasDent]

1. I think you are confused about the aldol reaction it occurs with reactants: aldehyde,aldehyde ; ketone,aldehyde ; and ketone,ketone - reacted with a base like NaOEt over heat to form an alpha,beta unsaturated aldehyde or ketone.
2. Where a hemiacetal/ketal reaction is with an aldehyde/ketone and 2 equivalents of the alcohol or 1 equivalent of something like ethane-1,2-diol which contains two alcohol groups on one molecule.
Hope that clears it up, sorry I didn't understand your initial question.

 

[mindblowing]

thanks now i got it