[NewtoAtoms]

Hello Organic Chemists

The behaviors of acyl chlorides and aldehydes in a reaction with a nucleophile are different because:

a.  the carbonyl carbon of the aldehyde is more positive   (THIS IS TRUE)
b.  The bulky chlorine sterically hinders nucleophilic attack at the carbonyl group (This is false because sp2 less sterically hindered)
c.  The acyl chloride cannot form a tetrahedral intermediate (FALSE)
d.  there is a good leaving group in acyl chloride (EEek.. this is true I think???  there is a good leaving chloride ion)
e.  the aldehyde has a readily oxidizable hydrogen (well hydrogen becomes bonded to the negatively polarized carbonyl oxygen)

I am thinking a is the correct answer, does anyone agree with me?
Thank you for your time!

Newtoatoms

[azmanam]

a is wrong.

[azmanam]

allow me to expand.  the possible answers, imho, are poorly worded.  You can't have comparative statements without comparing it to something.  So reword each answer in your head to complete the comparison.  Then evaluate.

a.  the carbonyl carbon of the aldehyde is more positive than the carbonyl carbon of the acid chloride. 
         ->The only difference is -H vs -Cl.  Chloride is more electronegative than a proton.  Chloride pulls more electron density away from the carbonyl carbon, thus the carbonyl carbon of the acid chloride 'is more positive' - i.e. has more partial positive charge - than the carbonyl carbon of the aldehyde.  A is false, and not the right answer.

etc...

[NewtoAtoms]

Hello azmanam,

Thank you for that explanation, I understand and realize my mistake. 
However I must then turn my attention to either d or e.  because both b and c are FALSE.

I will first reword the questions:

d.  There is a good leaving group in acyl chloride than in an aldehyde

     -->  An acyl chloride does have a leaving chloride ion, however when examining the mechanism of hydration of an aldehyde in a basic solution, there is not 'leaving group' other than a hydroxide ion. But unlike the acyl chloride there isn't really a leaving group.

e.  The aldehyde has a readily oxidizable hydrogen and an acyl chloride does not

     -->  to be honest I don't even really understand what this is saying.  I have wikipedia'd this and am realizing that perhaps it's trying to say that the H readily accept an O???  But this isn't the case, because generally it is the O of the aldehyde that accepts H (which is what I believe to be opposite to what the questions is saying?)

Would you be so kind to shed some further light azmanam.

I am grateful for your time.

Newtoatoms

[azmanam]

I dont' really know what e is asking either.  In organic reactions, you don't usually think about changing the oxidation state of hydrogen.  You usually only change the oxidation state of carbon.  You can ask your instructor exactly what was meant, but I can tell you e's not the correct answer.

[sjb]

b.  The bulky chlorine sterically hinders nucleophilic attack at the carbonyl group (This is false because sp2 less sterically hindered)
c.  The acyl chloride cannot form a tetrahedral intermediate (FALSE)

I'd actually think these are both true.

b. The chlorine is larger than hydrogen, so must hinder with some respect relative to the hydrogen. It may be that it's a better leaving group, so that the reaction and displacement occurs more readily when it occurs, but I don't see that as a steric issue.

c. Why do you feel that this is false? The steric bulk of the R group clearly prevents direct S_N2 attack and displacement of the chlorine "around the back side" of the carbonyl ...?

[azmanam]

re: b

but that's not what the question is asking.  the question is asking why acid chlorides react differently than aldehydes.  Acid chlorides react orders of magnitude faster than aldehydes.  The acid chloride is not going to react faster because the carbonyl carbon is more sterically hindered.   b may, technically, be true, but not within the confines of the question.

[NewtoAtoms]

RE: c

The acyl chloride CAN form a tetrahedral intermediate via this mechanism
 
           O                              R                                  R
           ll                               l                                   l
H2O + RCCl   <---slow---> H20-C-O- ----fast------> HO-C-OH
                                           l                                  l
                                           Cl                               Cl
                                                                        This is the tetrahedral intermediate.

[sjb]

Point taken, I misread part c, I'll have a think about b