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A Level Chemistry

Is it 3-chloropropene or 3-chloroprop-1-ene?
Reply 1
Avatar for liam.ro
liam.ro
11
It's 3-chloropropene.

Since there are three carbons in propene, there are only two places where you can have a C=C double bond. However, both C=C bonds will include a terminal carbon bond, so will both be 3-chloroprop-1-ene. (Another way to think about it is, the two possibilities are identical because flipping one molecule sideways will result in the other.) Hence, because both variations are essentially the same positional isomer, we call it propene without the need to specify carbon number.
Reply 2
Avatar for mani93786
mani93786
OP
11
Original post by liam.ro
It's 3-chloropropene.

Since there are three carbons in propene, there are only two places where you can have a C=C double bond. However, both C=C bonds will include a terminal carbon bond, so will both be 3-chloroprop-1-ene. (Another way to think about it is, the two possibilities are identical because flipping one molecule sideways will result in the other.) Hence, because both variations are essentially the same positional isomer, we call it propene without the need to specify carbon number.

Thanks! But would you then have to specify where the double bond is if there is a functional group of a higher priority, i.e. O-H or C=O? For example prop-1-en-1-ol or prop-2-en-1-ol.
Reply 3
Avatar for liam.ro
liam.ro
11
Original post by mani93786
Thanks! But would you then have to specify where the double bond is if there is a functional group of a higher priority, i.e. O-H or C=O? For example prop-1-en-1-ol or prop-2-en-1-ol.


Nope, you wouldn't have to because prop-2-ene doesn't exist. So because prop-1-ene is the only possibility, you only ever need to refer to it as propene.
Reply 4
Avatar for mani93786
mani93786
OP
11
Original post by liam.ro
Nope, you wouldn't have to because prop-2-ene doesn't exist. So because prop-1-ene is the only possibility, you only ever need to refer to it as propene.


You didn’t answer my question. I’m asking what if there’s an alcohol group attached to it? The alcohol would get the priority and hence the carbon attached to the O-H group would be C1. So then wouldn’t you have to number the position of the double bond? If on C1 or C2.
Reply 5
Avatar for liam.ro
liam.ro
11
Original post by mani93786
You didn’t answer my question. I’m asking what if there’s an alcohol group attached to it? The alcohol would get the priority and hence the carbon attached to the O-H group would be C1. So then wouldn’t you have to number the position of the double bond? If on C1 or C2.


My bad. In that case, yes, its exactly the way you just put it. Since the prioritised alcohol group is given a carbon number, you must also specify the position of the C=C bond; C1, C2 or C3.

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