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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: ying63 on July 30, 2021, 02:18:10 AM

Title: Mass Spectrometry
Post by: ying63 on July 30, 2021, 02:18:10 AM

Today at class we are asked to find the most common fragment of 1-Butanol from the Mass Spec graph. It has a base peak of 56, and while attempting to split the butanol, the closest molar mass that I could get was 57 (from removing the hydroxyl group). I tried to look for an explanation on the internet but couldn’t find any. What mistake have I made?

Thank you

Title: Re: Mass Spectrometry
Post by: Orcio_87 on July 30, 2021, 03:21:41 AM

What mistake ? Probably in calculations as 74 - 56 = 18, so the leaving group must have the molar mass equal 18.

Title: Re: Mass Spectrometry
Post by: ying63 on July 30, 2021, 03:33:16 AM

I removed the OH which only has a molar mass of 17 from CH3CH2CH2CH2OH, however I don't think I could further remove an extra Hydrogen, since the Hydrogen is bonded with the carbon, not the OH group

Title: Re: Mass Spectrometry
Post by: Orcio_87 on July 30, 2021, 05:43:16 AM

How then you explain mass of the main peak (56 u)?

Maybe it is that OH radical takes H from adjacent molecule?

After all HO-H is a stronger bond than aliphatic C-H.

Title: Re: Mass Spectrometry
Post by: ying63 on July 30, 2021, 06:43:43 AM

I think I understand now. Thanks :)