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chemistry aqa as level isomerism question

Which alkene shows E–Z isomerism?
A 2,3-dimethylbut-2-ene
B 4-methylpent-2-ene
C methylpropene
D pent-1-ene
the answer is B. i get why it's B but i don't get how it can't be C as well since one C is bonded to CH3 and H and the other C is bonded to CH3 and H
Original post by ricecakes1
Which alkene shows E–Z isomerism?
A 2,3-dimethylbut-2-ene
B 4-methylpent-2-ene
C methylpropene
D pent-1-ene
the answer is B. i get why it's B but i don't get how it can't be C as well since one C is bonded to CH3 and H and the other C is bonded to CH3 and H


I think that would be cis-trans
Original post by ricecakes1
Which alkene shows E–Z isomerism?
A 2,3-dimethylbut-2-ene
B 4-methylpent-2-ene
C methylpropene
D pent-1-ene
the answer is B. i get why it's B but i don't get how it can't be C as well since one C is bonded to CH3 and H and the other C is bonded to CH3 and H

Hey! I think it would help if you drew it out :smile:
Methylpropene would have a C=C bond with one carbon attached to two methyl groups and the other carbon attached to two hydrogens. Which means it's symmetrical and therefore can't be C.

Does this make sense?
Reply 3
Original post by aamina.hs
Hey! I think it would help if you drew it out :smile:
Methylpropene would have a C=C bond with one carbon attached to two methyl groups and the other carbon attached to two hydrogens. Which means it's symmetrical and therefore can't be C.

Does this make sense?

hi i drew the methyl group on the first carbon not the 2nd carbon, can u tell me why u assume it's on the 2nd carbon and not the 1st since the question doesn't specify
Original post by ricecakes1
hi i drew the methyl group on the first carbon not the 2nd carbon, can u tell me why u assume it's on the 2nd carbon and not the 1st since the question doesn't specify

Yeah ofc!
If you add the methyl group to the first carbon, that just increases the chain length by one and you end up with a 4-carbon chain. I'm assuming what u drew was something like this:

As you can see here, the highest carbon chain is length 4 so this would be called but-2-ene. This means, in a three carbon chain, the only place u can add a methyl group to is the centre carbon without it becoming a 4-C.

Does that help?
Reply 5
Original post by aamina.hs
Yeah ofc!
If you add the methyl group to the first carbon, that just increases the chain length by one and you end up with a 4-carbon chain. I'm assuming what u drew was something like this:

As you can see here, the highest carbon chain is length 4 so this would be called but-2-ene. This means, in a three carbon chain, the only place u can add a methyl group to is the centre carbon without it becoming a 4-C.
Does that help?

oh that makes sense yeah that's what i drew, thank u sm

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