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    My question is how do I know which functional groups/group of molecules am I meant to apply the E and Z stereo-isomerism drawing to?


    For example for the molecule 3-methylpent-2-ene

    CH3CH2=C(CH3)CH2CH3

    it has 2 CH3s on either side of the double bond and then a CH2CH3 and a H.

    So how am i meant to know which two should be on the same side for Z-stereoisomer?
    Is it meant to be the two CH3s or one CH3 and one CH3CH2 :confused:

    Also how am I meant to know for other molecules? Such as any question other than my example


    Thanks in advance
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    (Original post by user1-4)
    My question is how do I know which functional groups/group of molecules am I meant to apply the E and Z stereo-isomerism drawing to?


    For example for the molecule 3-methylpent-2-ene

    CH3CH2=C(CH3)CH2CH3

    it has 2 CH3s on either side of the double bond and then a CH2CH3 and a H.

    So how am i meant to know which two should be on the same side for Z-stereoisomer?
    Is it meant to be the two CH3s or one CH3 and one CH3CH2 :confused:

    Also how am I meant to know for other molecules? Such as any question other than my example


    Thanks in advance
    You apply the Cahn, Ingold, Prelog priorities rules

    Take a look at this interactive. Hover over each of the structures and it shows you the priority. It explains how you decide which groups have priority, but fundamentally it's the relative molecular mass of each atom in turn...
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    you need two different groups on each side of the double bond. if both the heavier groups or either side are on the same side (up down, not left right) then it's Z (think zimilar) if one is top side other bottom then its E
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    (Original post by Goods)
    you need two different groups on each side of the double bond. if both the heavier groups or either side are on the same side (up down, not left right) then it's Z (think zimilar) if one is top side other bottom then its E
    Thanks. I think I understand it. Do I just work out the Mr for each of the 4 corners?

    (Original post by charco)
    You apply the Cahn, Ingold, Prelog priorities rules

    Take a look at this interactive. Hover over each of the structures and it shows you the priority. It explains how you decide which groups have priority, but fundamentally it's the relative molecular mass of each atom in turn...

    Hi on the interactive, on the last page, doesn't the carboxylic acid have a greater priority (61) than the COH (29)?
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    (Original post by user1-4)
    Thanks. I think I understand it. Do I just work out the Mr for each of the 4 corners?




    Hi on the interactive, on the last page, doesn't the carboxylic acid have a greater priority (61) than the COH (29)?
    No, you take each atom in turn and compare them.

    The OH group has priority 16 .... 1

    While the COOH group has priority 12 ... 16 ...16 ....16 ....1

    So comparing the first atom the OH group takes priority.
 
 
 
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