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    QP
    http://www.ocr.org.uk/Images/131292-...-resources.pdf
    MS
    http://www.ocr.org.uk/Images/135168-...urces-june.pdf

    On 1b I can't understand how there are 22 hydrogens in the molecule, but I do undestand how there are 15 carbon. I've counted like 4 times . I get 26 hydrogens

    On 1cii I can't understand how you know that exactly 2 molecules of Br2 react. Since there is just one C=C bond in the molecule, surely just one Br2 molecule reacts.

    Thank you so much!
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    (Original post by krisshP)
    QP
    http://www.ocr.org.uk/Images/131292-...-resources.pdf
    MS
    http://www.ocr.org.uk/Images/135168-...urces-june.pdf

    On 1b I can't understand how there are 22 hydrogens in the molecule, but I do undestand how there are 15 carbon. I've counted like 4 times . I get 26 hydrogens

    On 1cii I can't understand how you know that exactly 2 molecules of Br2 react. Since there is just one C=C bond in the molecule, surely just one Br2 molecule reacts.

    Thank you so much!
    Maybe the attached images could help you visualize the reason why you have to get those two answers.

    This is what I always draw in my exams :P
    The purple lines represent "H-" bond.
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    Make sure that for each C atom, there are 4 bonds attached to it. You may be adding too many Hydrogens to some C atoms. Especially the ones with the double bonds in the 1st example - they wouldn't have any H atoms attached to them.

    For the c)ii) just remember - when the Bromine is added, the C=C opens up to form single bonds with a Br atom. So since there's 2 C=C bonds in rotundone, then that's 4 single bonds that can be formed. Therefore, it's 2 Br_{2}!
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    (Original post by freetown)
    Maybe the attached images could help you visualize the reason why you have to get those two answers.

    This is what I always draw in my exams :P
    The purple lines represent "H-" bond.
    For the diagram with the purple lines, look on the far RHS. With the two horizontal lines very close to one another, does that mean 2 C-C bonds or a single C=C? I thought it meant two C-C bond. I think this is my mistake since I recounted with the two close horizontal lines on the far RHS representing a single C=C bond and I ended up with the MS answer.
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    (Original post by freetown)
    Maybe the attached images could help you visualize the reason why you have to get those two answers.

    This is what I always draw in my exams :P
    The purple lines represent "H-" bond.

    (Original post by xfallingstar)
    Make sure that for each C atom, there are 4 bonds attached to it. You may be adding too many Hydrogens to some C atoms. Especially the ones with the double bonds in the 1st example - they wouldn't have any H atoms attached to them.

    For the c)ii) just remember - when the Bromine is added, the C=C opens up to form single bonds with a Br atom. So since there's 2 C=C bonds in rotundone, then that's 4 single bonds that can be formed. Therefore, it's 2 Br_{2}!
    Thanks so much for the nice help
 
 
 
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