# as chem stereoisomers

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#1
How would you determine which of the substituent groups has highest priority. I originally thought it would be the group with the highest mr but I think thats wrong
Last edited by idk__21; 4 months ago
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4 months ago
#2
(Original post by idk__21)
How would you determine which of the substituent groups has highest priority. I originally thought it would be the group with the highest mr but I think thats wrong
In normal cases, you look at the highest priority by seeing the atomic number of the atom, not the entire group. So for example, on the right side of the bond, you would look at C and H, not CH2OH and H.

Next, you see for whichever has the higher atomic number. Between C&H, C has a higher atomic number so that means that CH2OH would be the highest priority on the right side.

Now, coming to the left side. Both atoms are C & C, so their atomic number is same. This puts us in a pickle We then look at the next highest priority atoms adjacent to each of these carbons.

For the carbon atom in CH3CH2, the priority (in decreased order) is CHHH. For the carbon atom in CH3, the priority (in decreasing order) is HHH.

Since CH3CH2's adjacent atom (carbon in bold above) has a higher priority than the adjacent hydrogen atom in CH3 (in bold above), it follows that CH3CH2 will be of higher priority than CH3.

It's difficult to explain it in words, I suggest you visit this link once: https://www.chemguide.co.uk/basicorg/isomerism/ez.html and scroll down to the section "Extending the rules to more complicated molecules"
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#3
(Original post by qwert7890)
In normal cases, you look at the highest priority by seeing the atomic number of the atom, not the entire group. So for example, on the right side of the bond, you would look at C and H, not CH2OH and H.

Next, you see for whichever has the higher atomic number. Between C&H, C has a higher atomic number so that means that CH2OH would be the highest priority on the right side.

Now, coming to the left side. Both atoms are C & C, so their atomic number is same. This puts us in a pickle We then look at the next highest priority atoms adjacent to each of these carbons.

For the carbon atom in CH3CH2, the priority (in decreased order) is CHHH. For the carbon atom in CH3, the priority (in decreasing order) is HHH.

Since CH3CH2's adjacent atom (carbon in bold above) has a higher priority than the adjacent hydrogen atom in CH3 (in bold above), it follows that CH3CH2 will be of higher priority than CH3.

It's difficult to explain it in words, I suggest you visit this link once: https://www.chemguide.co.uk/basicorg/isomerism/ez.html and scroll down to the section "Extending the rules to more complicated molecules"
For the carbon on the left hand side of the carbon double bond I understand the bit where we look at the first atom but since that is both CC you said we look at the next highest priority. So does that means that for CH3CH2 other than the first Carbon, we look at the atom with the next highest atomic no ie the the next highest priority which would be C.? And for the CH3 other than the first C which already also appears in the CH3CH2 does that mean because there are only 3 H's the only highest priority can be H as that is the atom with highest atomic number left in the molecule?
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4 months ago
#4
(Original post by idk__21)
For the carbon on the left hand side of the carbon double bond I understand the bit where we look at the first atom but since that is both CC you said we look at the next highest priority. So does that means that for CH3CH2 other than the first Carbon, we look at the atom with the next highest atomic no ie the the next highest priority which would be C.? And for the CH3 other than the first C which already also appears in the CH3CH2 does that mean because there are only 3 H's the only highest priority can be H as that is the atom with highest atomic number left in the molecule?
Yes.

But remember that on the left since both are CC, we look at the next highest priority of the atoms attached to these carbon. In CH3CH2, the carbon is attached to 1 C and 2 H, whereas in CH3, the carbon is attached to 3 H.

Since CH3CH2’s next high priority atom C has higher atomic number than CH3’s next high priority atom, CH3CH2 becomes the higher priority
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4 months ago
#5
(Original post by idk__21)
How would you determine which of the substituent groups has highest priority. I originally thought it would be the group with the highest mr but I think thats wrong

it is the one with the highest mr but you take it atom by atom if that makes sense so for example in this one this is clearly a cis isomer (z) since if we take the left hand side the top group is the priority one as it has the highest mr and on the tight hand side the top is the priority group again
hope this makes sense🥰
it is the one with the highest mr but you take it atom by atom if that makes sense so for example in this one this is clearly a cis isomer (z) since if we take the left hand side the top group is the priority one as it has the highest mr and on the tight hand side the top is the priority group again
hope this makes sense🥰
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