Chemistry: Post your doubts here!

nehaoscar

nehaoscar

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princess Anu said:
http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf

Q29 ( ans is B)
30 (C) nd 20 (C) pleasee
Click to expand...

O29 : X is wrong as if you chose any one carbon atom and draw a 3D structure around it, you can see that all the 4 different substituents are in different planes. So since the C has another C as one of the 4 substituents, they are in different planes.
Y is wrong because for cis-trans, you need 2 same substituents on the 2 carbons, in this case there are not.
 
qwertypoiu

qwertypoiu

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princess Anu said:
http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf

Q29 ( ans is B)
30 (C) nd 20 (C) pleasee
Click to expand...
29 -All the carbon atoms bonded in the ring have tetrahedral structure, and are sp3 hybridised. this is because every carbon is attached to four groups. So like when you draw optical isomers, in fact, every carbon with 4 substituents have a 3 dimensional tetrahedral structure. Therefore, they cannot be on the same plane. Also, there is no Cis trans isomerism for a cycloalkene made up of less than 8 carbon atoms, since the ring constricts bond rotation. So neither students are correct.

30: the compound already given is:
CH3CH2CH2CO2CH3
Now just play around:
  1. CH3CH2CH2CO2CH3
  2. CH3CH(CH3)CO2CH3
  3. CH3CH2CO2CH2CH3
  4. CH3CO2CH2CH2CH3
  5. CH3CO2CH(CH3)CH3
  6. HCO2CH2CH2CH2CH3
  7. HCO2CH(CH3)CH2CH3
  8. HCO2CH2CH(CH3)CH3
  9. HCO2C(CH3)3

20. Again just play around

  1. CH3CH2CH2CH2CHO
  2. CH3CH2C*H(CH3)CHO
  3. OPTICAL ISOMER OF ABOVE
  4. CH3CH(CH3)CH2CHO
  5. C(CH3)3CHO
 
Mathemagical

Mathemagical

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Abdul Hanan said:
Thanks i do understand 27 and 29 now but can you please explain 22 a bit more? thanks again :)
Click to expand...
The keyword in Question 22 is "followed by". Take Option B, for example. After polymerising it, the alkene becomes saturated and therefore cannot undergo a reaction with cold, dilute KMnO4. Similarly, alkanes, which are also saturated, cannot undergo that reaction.
 
Metanoia

Metanoia

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nehaoscar said:
Q20:
View attachment 54222
The green line shows the main carbon chain. These are the 5 isomers
Click to expand...

Your bottom two isomers are identical.

Instead, find the chiral carbon in the 2nd isomer (top row), indicating that there is an extra optical isomer.

The question has hinted to look for optical isomers, so likely there will be at least one.
 
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