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Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

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Original post by jojo1995
Ah idk actually :redface: oops should have checked :tongue:

Thank you :smile:



Do we need to know how to name azo compounds ie the one I've taken a pic of ? image.jpg


Haven't ever seen that, so I have no idea :eek: I'm starting unit 5 again from thursday :frown:



Original post by James A
Guys, I don't get this. This is unit 4 stuff but we have to obviously recognise when a molecule displays optical isomerism.

For the image I uploaded, the book says there are two optical isomers of the molecule, but how do you know if the rotations cancel or not? Cheers

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Each chiral always has 2 enantiomers.... these 2 enantiomers always rotate the plane of polarized light in the opposite direction to eachother by the same amount. I kind of thought of them as like matter & anti-matter :smile:
Reply 1321
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AS01
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Original post by James A
Guys, I don't get this. This is unit 4 stuff but we have to obviously recognise when a molecule displays optical isomerism.

For the image I uploaded, the book says there are two optical isomers of the molecule, but how do you know if the rotations cancel or not? Cheers

Posted from TSR Mobile


rotation cancel what? the extent of rotating plane polarised light?
Original post by posthumus
Haven't ever seen that, so I have no idea :eek: I'm starting unit 5 again from thursday :frown:





Each chiral always has 2 enantiomers.... these 2 enantiomers always rotate the plane of polarized light in the opposite direction to eachother by the same amount. I kind of thought of them as like matter & anti-matter :smile:


Yeah but the book doesn't say that the two isomers cancel each other :/
Original post by James A
Yeah but the book doesn't say that the two isomers cancel each other :/


2 enantiomers formed via the same chiral center will always cancel each other out in that sense, I think they haven't mentioned it in unit 5 because it might have been in the unit 4 bit
Reply 1324
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Original post by James A
Yeah but the book doesn't say that the two isomers cancel each other :/


I know what u are confusing racemic mixture with.
Racemic mixture will have two different optical isomer but here its only one the other one can have CH3 can swap place with COOH so this will be another isomer.
So the one shown there rotates clockwise but the one with swapped places will rotate anti-clockwise hence no optical activity recorded :smile:
Does anybody know why 2-hydroxypropanphenylamine (3 carbon side chain with OH group on middle carbon/2ndary alcohol), reacts with 2,4-DNP?? I thought only carbonlys react with 2,4-DNP? It also doesnt react with felhlings or benedicts??

This is question 14 on multiple choice of Jan 2012
Original post by AtomicMan
Does anybody know why 2-hydroxypropanphenylamine (3 carbon side chain with OH group on middle carbon/2ndary alcohol), reacts with 2,4-DNP?? I thought only carbonlys react with 2,4-DNP? It also doesnt react with felhlings or benedicts??

This is question 14 on multiple choice of Jan 2012

Note that it says oxidation of compound X forms a substance which reacts with Brady's reagent.
When it's oxidised B will do both of the things it's meant to.
Original post by posthumus
2 enantiomers formed via the same chiral center will always cancel each other out in that sense, I think they haven't mentioned it in unit 5 because it might have been in the unit 4 bit




Original post by AS01
I know what u are confusing racemic mixture with.
Racemic mixture will have two different optical isomer but here its only one the other one can have CH3 can swap place with COOH so this will be another isomer.
So the one shown there rotates clockwise but the one with swapped places will rotate anti-clockwise hence no optical activity recorded :smile:



I get it now folkes !
Reply 1328
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Original post by James A
I get it now folkes !


:smile:
Original post by GeorgeL3
Note that it says oxidation of compound X forms a substance which reacts with Brady's reagent.
When it's oxidised B will do both of the things it's meant to.


Ahhhh, thanks :biggrin:
Original post by AS01
umm dont think we should except the one which is in the book. But then again if there are name for those compounds in book I think we might lol
I will go with we dont :tongue:



Original post by posthumus
Haven't ever seen that, so I have no idea :eek: I'm starting unit 5 again from thursday :frown:

Each chiral always has 2 enantiomers.... these 2 enantiomers always rotate the plane of polarized light in the opposite direction to eachother by the same amount. I kind of thought of them as like matter & anti-matter :smile:

Thanks guys, in that case I won't bother learning th :tongue:
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YAH
Original post by James A
I get it now folkes !


the two enantiomers should be equimolar for rotation to cancel, right?? A racemic mixture it is
Reply 1332
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Original post by YAH
the two enantiomers should be equimolar for rotation to cancel, right?? A racemic mixture it is


yes they should :smile:
Wow, the 7 day mark.
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Can I just compliment OP on the excellent poll for this thread.
Going to being joining this thread over the next few days.
why is the bromination of benzene first order with respect to both benzene and bromine??? (rate eqn)
Does anyone know whether ethanol reacts with water or oxygen in the fuel cell brethalyser?
Original post by AtomicMan
Does anyone know whether ethanol reacts with water or oxygen in the fuel cell brethalyser?


Ethanol is oxidized by oxygen
Original post by AtomicMan
Does anyone know whether ethanol reacts with water or oxygen in the fuel cell brethalyser?


The ethanol is oxidised by the oxygen :smile: EDIT: Looks like posthumus beat me to it again!
(edited 10 years ago)
Can anyone explain this bit about proton NMR to me.

butan-2-ol.bmp

This answer was referring to butan-2-ol, but I don't understand how they deduce that the splitting pattern is (2,6,1,5,3) ----- How do they come up with this?

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