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i cant figure this out

https://imgur.com/92m386Z


how to differentiate ?

here is the link to the sample assesment material--https://qualifications.pearson.com/content/dam/pdf/International%20Advanced%20Level/Chemistry/2018/Specification-and-Sample-Assessment/International-A-Level-Chemistry-SAMs.pdf
(edited 3 years ago)
Reply 1
Avatar for Interea
Interea
19
Original post by riamu
https://imgur.com/92m386Z


how to differentiate ?

here is the link to the sample assesment material--https://qualifications.pearson.com/content/dam/pdf/International%20Advanced%20Level/Chemistry/2018/Specification-and-Sample-Assessment/International-A-Level-Chemistry-SAMs.pdf

Since they're mixed in equimolar quantities, you need to find the pair that are different to each other, since then the rotations would "cancel out". Try visualising the second molecule in each pair, and see if you could rotate it to fit perfectly onto the first molecule - for 3 of the answers you should be able to.
Reply 2
Avatar for riamu
riamu
OP
9
Original post by Interea
Since they're mixed in equimolar quantities, you need to find the pair that are different to each other, since then the rotations would "cancel out". Try visualising the second molecule in each pair, and see if you could rotate it to fit perfectly onto the first molecule - for 3 of the answers you should be able to.

the right answer is B but it does not look like its mirror image since the hydrogen which is in the plane of paper in the first molecule is going into the page in the second molecule.please help
Reply 3
Avatar for Interea
Interea
19
Original post by riamu
the right answer is B but it does not look like its mirror image since the hydrogen which is in the plane of paper in the first molecule is going into the page in the second molecule.please help

Imagine them in 3D. If you left the hydrogen where it was and rotated the other 3 so that the bromine is in the same place, you can see that the other 2 have swapped places. If they were not mirror images, you would be able to rotate it to make all of the 4 sit on themselves.
Reply 4
Avatar for riamu
riamu
OP
9
Original post by Interea
Imagine them in 3D. If you left the hydrogen where it was and rotated the other 3 so that the bromine is in the same place, you can see that the other 2 have swapped places. If they were not mirror images, you would be able to rotate it to make all of the 4 sit on themselves.

what structure are you referring to (D?) because you are saying the position of hydrogen does not change (but it does change ) though i tried a 3D model on web but that took me some time to get the groups right but certainly i cant do that during exam
Reply 5
Avatar for Interea
Interea
19
Original post by riamu
what structure are you referring to (D?) because you are saying the position of hydrogen does not change (but it does change ) though i tried a 3D model on web but that took me some time to get the groups right but certainly i cant do that during exam

I'm talking about B since that's the one you referred to. If you line the hydrogen of the second molecule up with the hydrogen of the first molecule, you then have a triangle of the other 3 - if you were to look at it from the same side, can you create the same triangle order just using rotations, or would you have to reflect?

Sorry, it's a little tricky to explain over the internet without being able to gesture to explain what I mean!
Reply 6
Avatar for riamu
riamu
OP
9
Original post by Interea
I'm talking about B since that's the one you referred to. If you line the hydrogen of the second molecule up with the hydrogen of the first molecule, you then have a triangle of the other 3 - if you were to look at it from the same side, can you create the same triangle order just using rotations, or would you have to reflect?

Sorry, it's a little tricky to explain over the internet without being able to gesture to explain what I mean!

could you sketch it,pls with arrows to indicate which side to flip

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