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A-level chemistry queries

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  • hoay's Avatar
    189 posts since Jul '11
    • Simple molecular structures have intermolceualr forces.

      what about Giant covalent sturtucres. Do they have intermolecular forces? they have lots of strong covalent bonds which need very high eenrgy to be broken down.

      Except graphite which has VDW forces, in diamond if there are two units of diamond won't they have VDW forces bewteen them?  

       

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    15,023 posts since May '05
    • Originally posted by hoay:

      Simple molecular structures have intermolceualr forces.

      what about Giant covalent sturtucres. Do they have intermolecular forces? they have lots of strong covalent bonds which need very high eenrgy to be broken down.

      Except graphite which has VDW forces, in diamond if there are two units of diamond won't they have VDW forces bewteen them?  

       


      Yes, there are always van der Waals forces between molecules in close proximity, even giant ones. But such forces would exist only if you place 2 diamonds next to each other, touching. And even then, the van der Waals forces would be ridiculously weak (ie. just blowing onto 2 little diamonds can easily separate them), while the tetrahedral covalent lattice within each diamond (ie. that's one giant molecule for you, so gigantic that the diamond molecule is visible to your naked eye (otherwise your girlfriend would certainly dump you) and (if you're really rich) the diamond molecule might even be larger than your belly button) is so ridiculously strong, it's basically the hardest natural material known to man.

  • Alvinaash873's Avatar
    1 post since Feb '18
  • Heiskylhere1978's Avatar
    1 post since Mar '18
  • surveyUON's Avatar
    6 posts since Apr '18
  • Ngwengsamowo's Avatar
    1 post since Apr '18
    • Structural isomerism and stereoisomerism should be considered when answering this question. If a molecule contains two non-identical chiral carbon atoms, four optical isomers exist. How many isomers are there with

      ● molecular formula C7H14O and

      ● a five-membered ring and

      ● a tertiary alcohol group?

      A)4 B)5 C)9 D)13 

      Answer is C)9, WHY?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    15,023 posts since May '05
    • Originally posted by Ngwengsamowo:

      Structural isomerism and stereoisomerism should be considered when answering this question. If a molecule contains two non-identical chiral carbon atoms, four optical isomers exist. How many isomers are there with

      ● molecular formula C7H14O and

      ● a five-membered ring and

      ● a tertiary alcohol group?

      A)4 B)5 C)9 D)13 

      Answer is C)9, WHY?


      Structural isomers are (ethyl side-chain) + (1,2-dimethyl side-chains) + (1,3-dimethyl side-chains). The 2nd and 3rd structural isomers each have 2 chiral C atoms, hence 4 stereoisomers (eg. 1R,2R + 1R,2S + 1S,2R + 1S,2S). Hence total isomers = 1 + 4 + 4 = 9.

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