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Topic: Are these compounds the same product?  (Read 3617 times)

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Offline Montse

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Are these compounds the same product?
« on: March 16, 2015, 06:20:54 AM »
Hi all,

I am a Biologist and I lack organic chemistry knowledge. So it would be nice if some of you could help me with the following compounds. They all have the same Molecular Weight but different structure... The compound I work with is the N'-[(E)-(3,5-Dichloro-2-hydroxyphenyl)methylene]-2-nitrobenzohydrazide. Are the below compounds the same as the previous one??

3,5-dichloro-2-hydroxy-N-[(Z)-(2-nitrophenyl)methylideneamino]benzamide

3,5-dichloro-2-hydroxy-N-[(E)-(2-nitrophenyl)methylideneamino]benzamide

3,5-dichloro-2-hydroxy-N-[(2-nitrophenyl)methylideneamino]benzamide

Thank you in advance! :)

Bests,

Offline Dan

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Re: Are these compounds the same product?
« Reply #1 on: March 16, 2015, 06:40:35 AM »
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Offline mjc123

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Re: Are these compounds the same product?
« Reply #2 on: March 16, 2015, 09:31:25 AM »
It sounds as if your bold compound is HOCl2C6H2C=NNHCOC6H4NO2. The other 3 are geometrical isomers of
HOCl2C6H2CONHN=CHC6H4NO2. So no, they are not the same.

Offline Montse

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Re: Are these compounds the same product?
« Reply #3 on: March 17, 2015, 03:00:20 AM »
Thanks to both of you for the useful info!

So, being different compounds, do you think they can share some properties due to their similarities in the skeleton? Or is it like comparing strawberries and apples?

Thanks again
Bests,

Montse

Offline discodermolide

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Re: Are these compounds the same product?
« Reply #4 on: March 17, 2015, 04:27:10 AM »
It is like comparing "strawberries and apples".
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Offline Arkcon

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Re: Are these compounds the same product?
« Reply #5 on: March 17, 2015, 11:37:58 AM »
So, being different compounds, do you think they can share some properties due to their similarities in the skeleton? Or is it like comparing strawberries and apples?

I don't see how either analogy works better than an actual understanding of the underlying concepts.  Briefly, they have the same atoms, forming the same functional groups, in the same relation to each other.  Chemically, they should be identical.

Their seterochiostry is significantly different.  For a biochemical reaction, only one of them fits properly in an enzyme's catalytic pocket.  Only the correct one will work.

Here's a very simple example:  Glucose has one chiral center.  So it has two forms D- and L-.  Both burn in air in the same way.  Only the D- form is metabolizable by living things on Earth.  The L- form doesn't even fit in the receptor molecules in animal tongues, it tastes vaguely chemically, and slightly salty, not sweet.
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Offline Dan

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Re: Are these compounds the same product?
« Reply #6 on: March 18, 2015, 04:40:47 AM »
Here's a very simple example:  Glucose has one chiral center.  So it has two forms D- and L-.  Both burn in air in the same way.  Only the D- form is metabolizable by living things on Earth.  The L- form doesn't even fit in the receptor molecules in animal tongues, it tastes vaguely chemically, and slightly salty, not sweet.

While I see and agree with the point you are trying to make, there are some errors here, and perhaps this was not the best example. You are correct that that L-glucose is not metabolised, but glucose has 4 chiral centres (not 1) and L-glucose's sweetness is actually virtually indistinguishable from D-glucose.1 It was even investigated as a candidate for artifical sweeteners,2 but was a) too expensive to manufacture3 and b) causes what my PhD supervisor referred to as "fantastic osmotic diarrhea", which actually may have other useful applications.4 Where did you hear that L-glucose tastes salty?

1. Nature, 1969, 221, 555 link
2. Levin and Zehner in Alternative Sweeteners, 2nd ed 1991, chapter 7, p117 Link
3. Though it might be feasible now - the best chemical synthesis of L-glucose: Angew. Chem., Int. Ed. 2014, 1160 link
4. Gastrointestinal Endoscopy 2003, 30 link
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Offline Arkcon

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Re: Are these compounds the same product?
« Reply #7 on: March 18, 2015, 05:14:59 AM »
Thank you for that Dan:, I pretty much learned that the L-form of glucose wasn't metabolizeable in high school, and heard its taste was not sweet, as just the sort of object lesson I gave above -- chirality affects fitting in protein pockets either receptors or enzymes.  I'd never heard that L- form was ever sweet, but its flavor was an anecdote from somewhere else.  Thank you for the source.  And I should have seen there were more than one  chiral center in glucose.

Query:  there are 4 chiral centers in glucose.  Does each behave in the same way?  Only the typical biological one enters glycolosis, but do each of the others taste the same, but have an unfortunate ... non-absorbability?
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Offline Dan

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Re: Are these compounds the same product?
« Reply #8 on: March 18, 2015, 06:01:26 AM »
I don't quite understand the question:

Query:  there are 4 chiral centers in glucose.  Does each behave in the same way? 

Each chiral centre? Behave the same way in what sense?

Quote
Only the typical biological one enters glycolosis, but do each of the others taste the same, but have an unfortunate ... non-absorbability?

I am not aware of any sugars (monosaccharides) that don't taste sweet, but I have not checked for data on every single one so there may be some. In terms of osmotic diarrhea, the extent to which different sugars are absorbed in the gut varies and I don't know the approximate numbers for all of them or have a comprehensive reference. L-glucose is particularly poorly absorbed and so causes diarrhea after ingestion of quite small amounts (12g is enough according to this patent, compare to ~30 g of sucrose in a can of Coca Cola). D-Tagatose, which occurs rarely in nature and is used as a low calorie sweetener, is much more tolerated (and apparently <25% absorbed in pigs). You can see the symptoms experienced  in humans, and lots of poo tables, after a 29 g tagatose breakfast here.

This has to be the funniest table legend I have ever seen: TABLE 2: Distribution in Scores in Texture of the First
Defecation after the Experimental Breakfast.

I think maybe we should split this off as a separate topic Arkcon, we are veering some way from E/Z isomerism....
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