plz help with these ochem questions!

[skim1988]

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1. All of the following are routinely used in the lab to test for the presence of an aldehyde of a ketone functional group except:

a. tollen's test
b. schiffs test
c. iodoform test
d. bisulfite test
e. KMnO4 test

answer is E, KMnO4 test. But why cant KMnO4 be used to determine presence of aldehyde of ketone? Wouldn't the KMnO4 test be essentially the same as tollen's test because they both oxidize the aldehyde into carboxylic acid but does nothing to the ketone remains?

2. I attached a word doc for this problem. The answer is A but i thought D was the answer because it has fewer axial groups, and therefore, more stable. Also, D still has the methyl groups trans to each other.

 

[JustwantDDS]

for #2 it isnt asking for the most stable its telling you to interconvert what they gave you- everything moves down one and axial stays axial , eq stays eq

 

[skim1988]

o yea. lol you're right. wow i hope i dont make a stupid mistake like this on the real test.

 

[Demps]

1. All of the following are routinely used in the lab to test for the presence of an aldehyde of a ketone functional group except:

a. tollen's test
b. schiffs test
c. iodoform test
d. bisulfite test
e. KMnO4 test

answer is E, KMnO4 test. But why cant KMnO4 be used to determine presence of aldehyde of ketone? Wouldn't the KMnO4 test be essentially the same as tollen's test because they both oxidize the aldehyde into carboxylic acid but does nothing to the ketone remains?

2. I attached a word doc for this problem. The answer is A but i thought D was the answer because it has fewer axial groups, and therefore, more stable. Also, D still has the methyl groups trans to each other.

I'm not sure what bisulfite test is, based on the text I guess it tests for the aldehyde and ketone group.

KMnO4 is used to test the presence of alkene or alkyne I believe

 

[needzmoar]

answer is E, KMnO4 test. But why cant KMnO4 be used to determine presence of aldehyde of ketone? Wouldn't the KMnO4 test be essentially the same as tollen's test because they both oxidize the aldehyde into carboxylic acid but does nothing to the ketone remains?

Yes, KMnO4 is very oxidizing and will oxidize aldehydes. They also oxidize alkenes and alkynes as the previous poster mentioned. This is exactly why you wouldn't want to use KMnO4 to test for aldehydes because it could lead to false positives if alkenes or alkynes are present. The other reagents that are listed are mostly mild so their scope of reactivity is limited, therefore, ideal for a qualitative test of aldehydes.

 

[rah08e]

for #2 it isnt asking for the most stable its telling you to interconvert what they gave you- everything moves down one and axial stays axial , eq stays eq

for this all you need to do is change axial to equatorial and equatorial to axial, while keeping Stereochemistry the same.

 

[Demps]

Yes, KMnO4 is very oxidizing and will oxidize aldehydes. They also oxidize alkenes and alkynes as the previous poster mentioned. This is exactly why you wouldn't want to use KMnO4 to test for aldehydes because it could lead to false positives if alkenes or alkynes are present. The other reagents that are listed are mostly mild so their scope of reactivity is limited, therefore, ideal for a qualitative test of aldehydes.

good point. I almost forgot KMnO4 could oxidize aldehyde to carboxylic acids. Thanks~