The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

Mass spectrum of pentan-3-one



In the above example, the molecular ion has fragmented into the cation [CH3CH2CO]+ (because the Mr of this is 57)..

Would it be correct if you wrote [CH3CH2CO]+ as [C3H5O]+?

Also could the molecular ion fragment into the below (instead of the above):

[C4H9]+; since the Mr of this is also 57..

Thanks
Original post by sabre2th1
x


Yes, you can write it like that, but the structural formula is better as it's more detailed.

No it couldn't, as [CH3CH2CH2CH2]+ cannot be formed from CH3CH2COCH2CH3 (in terms of fragmentation), as in pentan-3-one, the oxygen is on the 3rd carbon, but there's no oxygen in [CH3CH2CH2CH2]+.
(edited 11 years ago)
Reply 2
Avatar for sabre2th1
sabre2th1
OP
12
Original post by thegodofgod
Yes, you can write it like that, but the structural formula is better as it's more detailed.

No it couldn't, as [CH3CH2CH2CH2]+ cannot be formed from CH3CH2COCH2CH3 (in terms of fragmentation), as in pentan-3-one, the oxygen is on the 3rd carbon, but there's no oxygen in [CH3CH2CH2CH2]+.


So each element (from the molecular ion) has to be present in the cation? And the number of atoms of each element present doesn't matter (as long as there is at least 1 atom of each, and overall it adds up to the peak's M/Z value)?
(edited 11 years ago)
Original post by sabre2th1
So each element (from the molecular ion) has to be present in the cation? And the number of atoms of each element present doesn't matter (as long as there is at least 1 atom of each, and overall it adds up to the peak's M/Z value)?


No, sorry, what I wanted to express was that if you split [CH3CH2COCH2CH3]+ in any way, there is no way you can get [CH3CH2CH2CH2]+.

What you've written above isn't correct :no:
Reply 4
Avatar for sabre2th1
sabre2th1
OP
12
Original post by thegodofgod
No, sorry, what I wanted to express was that if you split [CH3CH2COCH2CH3]+ in any way, there is no way you can get [CH3CH2CH2CH2]+.

What you've written above isn't correct :no:


Oh I see. So in an exam question, if you were asked to write down the structural formula for a cation, how would you know if its right?

Cheers
Original post by sabre2th1
Oh I see. So in an exam question, if you were asked to write down the structural formula for a cation, how would you know if its right?

Cheers


You can normally work the structural formula out :smile:
Reply 6
Avatar for sabre2th1
sabre2th1
OP
12
Original post by thegodofgod
You can normally work the structural formula out :smile:


Oh okay, thank you :smile:

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you