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    I had a question to write the structural formula of 2-methylbutanoic acid. My answer was CH_3CH_2CH(CH_3)COOH, however the actual answer is CH_3CH(CH_3)COOH.

    Can someone explain why?
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    you are right. Answer given is wrong
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    The 'actual' answer is wrong, yours is correct. When you add substituents to a main chain, whether it be methyl, chloride, phenyl, thiol or whatever, you don't count those atoms in the main-chain name. So what you did was right.

    Where is the 'actual' answer from? What they have is 2-methylpropanoic acid
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    What. Isn't that right? o.o
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    Mhmm, that's my understanding of it, however their answer only has three carbons in the longest chain, as the methyl group is a side chain?
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    Ahh okay, thanks .

    It's from the heinneman OCR revision guide.
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      (Original post by ViralRiver)
      Ahh okay, thanks .

      It's from the heinneman OCR revision guide.
      Clearly they need to revise the topic themselves then.
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      (Original post by mathew551)
      What. Isn't that right? o.o
      The answer has that second carbon bonding only 3 times I think....and obviously carbon has a valency of 4 so its gotta be CH2 not CH

      actually i'm now too lol.
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      (Original post by ViralRiver)
      Ahh okay, thanks .

      It's from the heinneman OCR revision guide.
      I wouldn't worry, there are mistakes in guides like this. I once saw a GRE Chemistry prep book that had a mistake on every other page, almost. I just ran those structures through ChemDraw to double check and it's indeed correct. If you're in doubt, imagine there being a chloride or something in which case you would say 2-chlorobutanoic acid. It would only change the name if there was an C-chain longer than the other chain (which you would have spotted in the first place)
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      (Original post by Wilzyy)
      The answer has that second carbon bonding only 3 times I think....and obviously carbon has a valency of 4 so its gotta be CH2 not CH
      The second carbon is bonded to 4 other groups:
      1) the carboxyl group
      2) a methyl
      3) an ethyl
      4) a hydrogen.

      tetravalency maintained
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      You are correct
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      Okay thanks a lot ^_^ . I have another question now ><

      Complete this equation: CH_3CH(CH_3)COOH+Mg\rightarrow

      Okay, so I read through the book etc, and was given examples on how carboxylic acids react with metals, and using sodium, I get the following: C_6H_5COOH+Na\rightarrow C_6H_5COO^-Na^++\frac{1}{2}H_2, however I can't do the same method for the above question.

      Their answer is 2CH_3CH(CH_3)COOH+Mg\rightarrow (CH_3CH(CH_3)COO^-)_2Mg+H_2

      Can someone explain why it doesn't work for Mg as well?
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      I know they're in different groups, but the book says that my method applies for reactive metals. As far as I know, group 2 metals are reactive.
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      (Original post by ViralRiver)
      Okay thanks a lot ^_^ . I have another question now ><

      Complete this equation: CH_3CH(CH_3)COOH+Mg\rightarrow

      Okay, so I read through the book etc, and was given examples on how carboxylic acids react with metals, and using sodium, I get the following: C_6H_5COOH+Na\rightarrow C_6H_5COO^-Na^++\frac{1}{2}H_2, however I can't do the same method for the above question.

      Their answer is 2CH_3CH(CH_3)COOH+Mg\rightarrow (CH_3CH(CH_3)COO^-)_2Mg+H_2

      Can someone explain why it doesn't work for Mg as well?
      It's the same reaction, just involving 2 electrons in the case of magnesium as opposed to 1 in the case of Na. Basically, Mg goes to Mg2+, being a second group element. Radical Mg1+ would be very unstable and immediately react to form Mg and Mg2+. Mg2+ is a dication and formally needs 2 charges to create a salt, hence 2 acid anions in the equation. H+ going to H is a 1-electron reduction, that's why you need 2 of those as well. Makes sense?
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      (Original post by =gabriel=)
      It's the same reaction, just involving 2 electrons in the case of magnesium as opposed to 1 in the case of Na. Basically, Mg goes to Mg2+, being a second group element. Radical Mg1+ would be very unstable and immediately react to form Mg and Mg2+. Mg2+ is a dication and formally needs 2 charges to create a salt, hence 2 acid anions in the equation. H+ going to H is a 1-electron reduction, that's why you need 2 of those as well. Makes sense?
      Ahh perfect, thanks ^_^ .
     
     
     
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