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Topic: most oxidized molecule  (Read 13318 times)

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Offline a confused chiral girl

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most oxidized molecule
« on: May 18, 2007, 04:02:47 AM »
hi,

I have this question with no answer key...so if anyone can please correct me and tell me the right answers, please help me.

I am looking for the overall system that is most oxidized , least oxidized and 2 that are at the same overall oxidation level.

for A) I have 3 O (since double bond to O counts as 2..) and 7H
B) 4 O and 8 H
C) 4 0 and 4 H
D)  3 O  and 4 H
E)  2 O and 6H

I have attempted this question..so please let me know the correct answers. here are my thoughts - most oxidized is C) because it has the most O and the least H.  least oxidized is E) because it has the fewest O atoms. same oxidation level is A & B or A & E? because when you subtract the # of O from H, you get "4" for all three of them...so how do we know which 2 are at the same level?

thank you!!

Offline alphahydroxy

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Re: most oxidized molecule
« Reply #1 on: May 18, 2007, 04:17:24 AM »
I think your answers are right. As far as the 2 that are at the same oxidation level, think about the number of bonds to oxygen, and the number of double bonds in each molecule.

Offline a confused chiral girl

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Re: most oxidized molecule
« Reply #2 on: May 18, 2007, 04:28:14 AM »
if E) is the least oxidized..then how can A) and E) be at the same oxidation level?


Offline alphahydroxy

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Re: most oxidized molecule
« Reply #3 on: May 18, 2007, 06:10:14 AM »
then how can A) and E) be at the same oxidation level?

Sorry, I didn't mean to imply that this was correct...

Think about the number of bonds to oxygen, and the level of unsaturation in each molecule. It may also help to consider that structure A could be (correctly) drawn in another form...


(incidenatally, notice how my structures look better than yours - paticularly if you click on it and open with a viewer -  because I used a chemical drawing program ;)  )

Offline AWK

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Re: most oxidized molecule
« Reply #4 on: May 18, 2007, 06:49:09 AM »
I undestand that you want to obtain a mean oxidation number for these compounds.
Then use -2 for oxygen and +1 for hydrogen.
A formal six carbon residue will then have -4, -4, 0, -2 and -4 charge for structures A to E, respectively, and the highest oxidation state shows structure C, and the lowest oxidation state show structures A, B and E
AWK

Offline alphahydroxy

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Re: most oxidized molecule
« Reply #5 on: May 18, 2007, 06:56:31 AM »
I undestand that you want to obtain a mean oxidation number for these compounds.
Then use -2 for oxygen and +1 for hydrogen.
A formal six carbon residue will then have -4, -4, 0, -2 and -4 charge for structures A to E, respectively, and the highest oxidation state shows structure C, and the lowest oxidation state show structures A, B and E

I'm not sure I follow you here. Surely the formal oxidation state of all these compounds must be zero, as they are all neutral species...?

Or am I just having a blonde moment ? ;)

Offline AWK

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Re: most oxidized molecule
« Reply #6 on: May 18, 2007, 07:06:01 AM »
I counted formal number of electrons for six carbon atoms. Oxidation states can be obtaned by dividing these numbers by 6, but for comparison (without calculation of ON) you can look at the lowest and the highest numbers above.
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Offline alphahydroxy

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Re: most oxidized molecule
« Reply #7 on: May 18, 2007, 09:14:36 AM »
To be honest, I still don't really follow where those numbers come from - but this is probably my problem as I've never really thought about the oxidation states of wholly organic compounds in terms of numerical values.

I personally find it much easier to think of say, A, B and C as all having 2 carbons at the ketone oxidation level, and then to consider any double bonds present.

Offline AWK

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Re: most oxidized molecule
« Reply #8 on: May 18, 2007, 09:46:03 AM »
OK, may this helps you. My previous explanation is equivalent to this one.
AWK

Offline alphahydroxy

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Re: most oxidized molecule
« Reply #9 on: May 18, 2007, 11:46:54 AM »
Thanks for that! I think I'm getting there...

So, as far as I can see, a single bond to oxygen gives a count of +1 (or -1 going on your original explantion, I guess the "phase" of the number doesn't matter? ), and a bond to hydrogen gives -1. So the double bonds are accounted for implicitly, rather than explicitly.

Am I on track? I do appreciate this is something I really should know, but I haven't thought along these lines in some considerable time...! :$

Offline AWK

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Re: most oxidized molecule
« Reply #10 on: May 18, 2007, 12:36:11 PM »
Forget about any bonds between two atoms of the same kind.
Hence -CO- ON for C=-2
-CHOH- ON for C=0
and so on
AWK

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