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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: AussieKenDoll on August 12, 2020, 09:52:50 AM

Title: Which peak is the Molecular Ion peak in MS?
Post by: AussieKenDoll on August 12, 2020, 09:52:50 AM
Molecular Ion peak has the highest m/z ratio, according to this mass spectrum ,Molecular Ion peak is the 216 or the 219?
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: MOTOBALL on August 12, 2020, 10:20:02 AM
The molecular ion is taken as that composed of the lowest atomic mass of each element.
Thus, 12C, 1H, 16O,14N, 35Cl, 32S etc
For “small” molecules, less than about 1000 amu, the mol. ion will usually be the most intense peak in the mol. ion cluster.
For chloro-benzophenone it is m/z 216.

Regards,
Motoball
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: AussieKenDoll on August 12, 2020, 10:47:58 AM
The molecular ion is taken as that composed of the lowest atomic mass of each element.
Thus, 12C, 1H, 16O,14N, 35Cl, 32S etc
For “small” molecules, less than about 1000 amu, the mol. ion will usually be the most intense peak in the mol. ion cluster.
For chloro-benzophenone it is m/z 216.

Regards,
Motoball
What are the 3 small peaks after 216 peak?
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: Corribus on August 12, 2020, 10:50:18 AM
What do you know about most atoms? Do you have exact masses of those peaks?
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: AussieKenDoll on August 12, 2020, 11:22:08 AM
I understand now that the molecular ion peak is the 216 and other small peaks after 216 are isotopic peaks!
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: Corribus on August 12, 2020, 01:18:50 PM
Correct. In theory, the relative intensities of the isotopic peaks can tell you something about the number of carbons in the molecule.
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: Babcock_Hall on August 12, 2020, 03:13:17 PM
Ken,

I would call your attention to the peak at 218.
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: AussieKenDoll on August 12, 2020, 03:14:47 PM
what is that peak 218? It is a isotope peak right?
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: Babcock_Hall on August 12, 2020, 03:29:28 PM
It is an isotope peak.  Why do you think it is larger than the peak at 217?
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: AussieKenDoll on August 12, 2020, 03:31:46 PM
may be peak at 217 could be branched and peak at 218 is not or less branched!
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: AWK on August 12, 2020, 03:36:37 PM
https://www.lfd.uci.edu/~gohlke/molmass/?q=C13H9ClO
Title: Re: Which peak is the Molecular Ion peak in MS?
Post by: Babcock_Hall on August 12, 2020, 07:59:38 PM
may be peak at 217 could be branched and peak at 218 is not or less branched!
I don't know what you mean by "branched."  In any case there is a simple explanation, as suggested by AWK.