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AQA CHEM4 - 13th June 2012

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Could somebody explain 4)c)ii) to me please? I don't understand the mechanism they are using to get the product?!

http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM4-W-QP-JAN11.PDF
http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM4-W-MS-JAN11.PDF

I think it's because Y is made up of a hydroxy OH group and a COOH group, elimination always involves the formation of a C=C, this happens as the oh group is removed and the lone pairs on the O attack a H on the middle carbon forming a water molecule and C=C. It's an AS mechanism I think, I hope that helped :smile:

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(edited 11 years ago)

Reply 561

Baraa3

Original post by nmudz_009

Can somebody explain why a racemic mixture is NOT made wen propanone reacts with HCN? It does with Ethanal

I think its because when it propanone reacts with HCN it doesn't form an optical isomer, it doesn't have a chiral centre carbon hence it will not rotate a plane of plane polarised light, whereas ethanal does form an optical isomer as it has a carbon chiral centre where it is able to rotate when passed through a plane of plane polarised light forming a racemic mixture. hope this helps :smile:

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Reply 562

Casshern1456

Original post by nmudz_009

Can somebody explain why a racemic mixture is NOT made wen propanone reacts with HCN? It does with Ethanal

Draw the reaction of propanone with KCN it is not a racemate because it does not have 4 different groups on the central Carbon.

With ethanal it forms 4 different groups.

Reply 563

CollateralElement

Original post by Parle à ma main

Yeah, that's right, you use moles = mV/ 1000
the V = the original volume + however much water has been added

Is there any specific question from a paper you're thinking of? :smile:

Many of the papers refer to questions like this in the pH calculation section. I just always get stuck.

For example: 2aiii Jan 2011 paper: Calculate the pH of the solution formed when 10.0cm³ of 0.154moldm^-3 HCl are added to 990cm³ water.

I mean... What d'you do? It's only two marks and I feel like an idiot for not knowing...

I can figure that the overall cm³ is 1000 and that it is 1dm³ but using the concentration x volume = moles equation, I can't get 1.54x10^-3 .... What am I doing wrong?

Reply 564

CollateralElement

Anyone got any notes or easy tips for the whole organic synthesis topic? .....We've only recently finished and my A3 poster is far too confusing.

Reply 565

Baraa3

Original post by CollateralElement

Anyone got any notes or easy tips for the whole organic synthesis topic? .....We've only recently finished and my A3 poster is far too confusing.

I just memorised everything, like I'd look at all the reactions that involve a haloalkane and memorise them and then once I've got that I'd do all the reactions of an alkene, I'd love to know if there was an easier less memorising way but everyone I've asked did the same, good luck with it try covering the sections your focusing on and draw what you can remember, don't focus on a lot at a time though.

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Reply 566

Doctor.

Original post by nmudz_009

Can somebody explain why a racemic mixture is NOT made wen propanone reacts with HCN? It does with Ethanal

I would have thought they both do.

Well anyway, its due to the moecule being planer. So the CN Nucleophile can attack from above and below the plane, equally.

Reply 567

Doctor.

Original post by CollateralElement

Hey well firstly, convert that "10.0cm³ of 0.154moldm^-3 HCl"
In to moles. Then just throw it Into the n= MV/1000 formula! See what you get :smile:

rather mean for 2 marks tbh

Reply 568

Glacier

Original post by Doctor.

I would have thought they both do.

Well anyway, its due to the moecule being planer. So the CN Nucleophile can attack from above and below the plane, equally.