Mass Spectrometry question

Are you saying there should be a peak for 15 for ethanol? The 15 peak is more likely to be seen in methoxymethane and that seems like a more sensible answer.

The book contradicts itself, so that can't be trusted :rolleyes:

Reply 2

OP

Original post by EierVonSatan

Are you saying there should be a peak for 15 for ethanol? The 15 peak is more likely to be seen in methoxymethane and that seems like a more sensible answer.

The book contradicts itself, so that can't be trusted :rolleyes:

Yeah, but the figure in the book doesn't show that peak (maybe it's because of low resolution) :s-smilie:

.

Just another point - it may be because of the fact that I'm misreading the question! Does the book mean that which fragment's peak appear on the spectrum of methoxymethane, but not on that of ethanol? It may be just another point that charge to mass of ratios of [CH₃O]⁺ and [CH₂OH]⁺ are same. . . :rolleyes:

Reply 3

Just another point - it may be because of the fact that I'm misreading the question! Does the book mean that which fragment's peak appear on the spectrum of methoxymethane, but not on that of ethanol? It may be just another point that charge to mass of ratios of [CH₃O]⁺ and [CH₂OH]⁺ are same. . . :rolleyes:

I don't think you're interpreting the question wrong, it's looking for a peak that would be on methoxymethane's spectrum but not on ethanol's.

I'm unfamiliar of how much you're expected to cover on this topic. As far as I can see the question is nonsense and I'd move on if I were you :p:

Reply 4

OP

Original post by EierVonSatan

I don't think you're interpreting the question wrong, it's looking for a peak that would be on methoxymethane's spectrum but not on ethanol's.

I'm unfamiliar of how much you're expected to cover on this topic. As far as I can see the question is nonsense and I'd move on if I were you :p:

Many thanks! :tongue:

Reply 5

OP

Hello again, I've got another question. :colondollar:

About the mass spectrum of molecule containing two bromine atoms, the book says, "The M, [M +2] and [M + 4] peaks also occur in dibromomethane but the relative heights are easier to work out. Because the ratio ⁷⁹Br:⁸¹Br is 1 : 1, we get the M : [M + 2] : [M + 4] height ratio as 1 : 2 : 1"

My question is that shouldn't the M : [M + 2] : [M + 4] height ratio be 1 : 1 : 1? Or am I missing a bit of maths? :confused:

-Thanks

Reply 6

Original post by Zishi

Hello again, I've got another question. :colondollar:

About the mass spectrum of molecule containing two bromine atoms, the book says, "The M, [M +2] and [M + 4] peaks also occur in dibromomethane but the relative heights are easier to work out. Because the ratio ⁷⁹Br:⁸¹Br is 1 : 1, we get the M : [M + 2] : [M + 4] height ratio as 1 : 2 : 1"

My question is that shouldn't the M : [M + 2] : [M + 4] height ratio be 1 : 1 : 1? Or am I missing a bit of maths? :confused:

-Thanks

List the combinations:

79 + 79 = M
79 + 81 = M + 2
81 + 79 = M + 2
81 + 81 = M + 4

so there would be a 1 : 2 : 1 ratio (it will follow pascals triangle :smile:

)

Reply 7

OP

Original post by EierVonSatan

List the combinations:

79 + 79 = M
79 + 81 = M + 2
81 + 79 = M + 2
81 + 81 = M + 4

so there would be a 1 : 2 : 1 ratio (it will follow pascals triangle :smile:

)

Wow, things are rarely as simple as they seem to be! Many thanks. :biggrin:

Reply 8

123alpha

1

Hello! The answer is right in the book as the question is asking for a fragment that is possible in methoxymthane but not in ethanol. Remember that different fragments can have the same mass. If we compare the structure of ethanol and methoxymethane then we will find that CH3O+ fragment is only possible in methoxymethane structure.

Reply 9