Destroyer #10

[Mit Lu]

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I have the 2006 version so I don't know if its the same on newer revisions. It says, Which of these compounds will not undergo an Aldol Condensation?
a) Acetone
b) Benzaldehyde
c) Formaldehyde
d) Pentanal
e) Neither B or C

The solution says that only if the aldehyde or ketone has an alpha hydrogen could an Aldol occur. It says that benzaldehyde and formaldehyde lack alpha hydrogens thus will not undergo the Aldol condensation, so the correct answer is E. I see that formaldehyde does not have an alpha hydrogen but don't see how benzaldehyde does not have one. Looking at the structure it looks like it has an alpha hydrogen. What am I not getting here? Anyone know?

Also, the O-chem destroyer is kicking my butt... is the real DAT a little easier than destroyer?

 

[prsndwg]

benzaldehyde doesnt have alpha hydrogen b/c when it is connceted to the carbonyl, there is no place left for hydrogen on benzene ring(too many bonds).
hope this makes sense..

 

[nze82]

I have the 2006 version so I don't know if its the same on newer revisions. It says, Which of these compounds will not undergo an Aldol Condensation?
a) Acetone
b) Benzaldehyde
c) Formaldehyde
d) Pentanal
e) Neither B or C

The solution says that only if the aldehyde or ketone has an alpha hydrogen could an Aldol occur. It says that benzaldehyde and formaldehyde lack alpha hydrogens thus will not undergo the Aldol condensation, so the correct answer is E. I see that formaldehyde does not have an alpha hydrogen but don't see how benzaldehyde does not have one. Looking at the structure it looks like it has an alpha hydrogen. What am I not getting here? Anyone know?

Also, the O-chem destroyer is kicking my butt... is the real DAT a little easier than destroyer?

Do you see an alpha hydrogen here?
The alpha carbon already has 4 bonds, so it can't have an alpha hydrogen.
The other Hydrogen (the one to the right) isn't considered an alpha hydrogen, because it's not connected to an alpha carbon.

 

[Mit Lu]

nze82, got it. I was an idiot and didnt count the bonds that the C had (4), hence no H. Thanks