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  • iSean's Avatar
    38 posts since Oct '15


    • Hi UltimaOnline :P 
      Mind solving this question for me?
      I'd provided the possible structures for dichorobenzene. 

       

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
  • iSean's Avatar
    38 posts since Oct '15
    • Originally posted by UltimaOnline:


      Edited : my bad, but this is an idiotic qn!

      Not really. I wanna see your opinions haha. 
      Because my answer is 3. 

      Examiner Reports for this paper haven't came out. :P

      Edited by UltimaOnline 13 Mar `17, 1:07AM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
    • Originally posted by iSean:

      Not really. I wanna see your opinions haha. 
      Because my answer is 3. 

      Examiner Reports for this paper haven't came out. :P


      Edited : my bad, but this is an idiotic qn!

      Edited by UltimaOnline 13 Mar `17, 1:07AM
  • iSean's Avatar
    38 posts since Oct '15
    • Originally posted by UltimaOnline:


      Edited : my bad, but this is an idiotic qn!

      Ease of questioning you to explain to me why is not 3. biggrin.png

      Basically this isn't a question that most teachers really touch on, or just my college only. 
      Where most students can answer it either be 4, 5 or 6. 

      Edited by UltimaOnline 13 Mar `17, 1:07AM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
    • Originally posted by iSean:

      Ease of questioning you to explain to me why is not 3. biggrin.png

      Basically this isn't a question that most teachers really touch on, or just my college only. 
      Where most students can answer it either be 4, 5 or 6. 


      Edited : my bad, but this is an idiotic qn!

      Edited by UltimaOnline 13 Mar `17, 1:07AM
  • iSean's Avatar
    38 posts since Oct '15
    • Originally posted by UltimaOnline:


      Edited : my bad, but this is an idiotic qn!

      Well, I'd "solved" it. But not technically the answer wanted by Cambridge, which is B. Hence I seek your wisdom, @UltimaOnline.  
      Apparently they were looking for 4 structures.

      So I only can conclude that Structure 4. Is what they wanted. 
      As 5 and 6 correspond back to 2 and 3. 

      But under the resonant state does really 1 and 4 couldn't consider as one?

      Edited by UltimaOnline 13 Mar `17, 1:08AM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
    • Originally posted by iSean:

      Well, I'd "solved" it. But not technically the answer wanted by Cambridge, which is B. Hence I seek your wisdom, @UltimaOnline.  
      Apparently they were looking for 4 structures.

      So I only can conclude that Structure 4. Is what they wanted. 
      As 5 and 6 correspond back to 2 and 3. 

      But under the resonant state does really 1 and 4 couldn't consider as one?


      Ah yes, you're right. It's my bad, in failing to recognize it's a matter of 'camera angle', why 2 = 5 and 3 = 6.

      But it's also Cambridge's (and all Singapore JCs and Malaysian schools who set such questions) bad, for setting such an idiotic question. It's idiotic because cyclohex-1,3,5-triene doesn't and cannot exist, and so questions shouldn't be set on it. Also, calling it "Kekule structure" is erroneous, even if Mr Kekule himself got it wrong back then. Kekule structure = Lewis structure (originally, slight difference, but these days they're used interchangeably). Cyclohex-1,3,5-triene should be called "resonance contributor" of benzene, not "Kekule structure" of benzene.

      To answer your question, in the real world, ie. resonance hybrid, 1 = 4. But in human minds, ie. resonance contributor, 1 not = 4. Your confusion proves my point, this is an idiotic question.

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    • The Chemical Mystery of the Kim Jong Nam Assassination (and why 2 separate women assassins were required) :

      https://sg.news.yahoo.com/toxic-mystery-behind-kim-jong-nams-assassination-045311729.html

  • Carychidestar's Avatar
    11 posts since Jan '17
    • Hi ultima,could you help me to solve this question?

      I got negative values....

      "0.7g of a hydrocarbon K was burnt completely in excess dry oxygen.2.2g of co2 is formed.100cm3 of K required 600cm of o2 gas,measured at same temp and pressure for complete combustion.Determine the molecular formula of K."

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
    • Originally posted by Carychidestar:

      Hi ultima,could you help me to solve this question?

      I got negative values....

      "0.7g of a hydrocarbon K was burnt completely in excess dry oxygen.2.2g of co2 is formed.100cm3 of K required 600cm of o2 gas,measured at same temp and pressure for complete combustion.Determine the molecular formula of K."


      Hi Carychidestar,

      (x + y/4) = 6

      [ 0.7 / (12x + y) ] x = [ 2.2 / 44 ]

      Solve the simultaneous equations.

  • CKTR's Avatar
    82 posts since Jun '15
    • Hi, I have a question, for N2014/P3/Q2(d),(e) why does the cyclic compound form an aliphatic compound after adding LiAlH4? I understand that the ketone group will be reduced to an alcohol but unsure about the ester functional group.... thanks

      Edited by CKTR 20 Mar `17, 9:19PM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    10,820 posts since May '05
    • Originally posted by CKTR:

      Hi, I have a question, for N2014/P3/Q2(d),(e) why does the cyclic compound form an aliphatic compound after adding LiAlH4? I understand that the ketone group will be reduced to an alcohol but unsure about the ether functional group.... thanks


      LiAlH4 reduces ester group into 2 alcohols, at least one of which will be a primary alcohol (since it was obtained from the carboxylic acid part of the ester).

      No prob.

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