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OCR Chemistry - mass spectroscopy

This is for the exam tomorrow so any help would be much appreciated!!! :eek:

It's just a general question - in the mark schemes, with mass spectroscopy questions, the molecular ion peak is often described as that furthest to the right or that with the highest m/e value but surely it is the second to last peak which will be the second fuirthest from the right with the second highest m/e value? Can anyone help explain this? If I write "the molecular ion peak - i.e. that with the second highest m/e value" in the exam, will I lose marks for it?

Thanks.
Yes, you'll lose3 marks because it isn't!

It's the highest m/e ratio peak - don't confuse yourself, just stick to that.
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dob-bo
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Hi...I've done the exam now so I guess it doesn't matter any more but I am still curious...I thought the last peak was due to the M + 1 ion? (the possible presence of C13 in some isomers) so won't this be the last peak and have the highest m/e value?
This is still the molecular ion only with different isotopes! Clearly the heaviest isotope mix will give the peak with the highest m/e ratio.

The highest peak is due to [M]+

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