Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Robin97 on December 09, 2017, 11:37:14 AM

Title: Mass Spectrum of Hexanoic Acid
Post by: Robin97 on December 09, 2017, 11:37:14 AM

I have to explain the fragmentation patterns of Hexanoic Acid, but i fail to do so.
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwebbook.nist.gov%2Fcgi%2Fcbook.cgi%3FSpec%3DC142621%26amp%3BIndex%3D0%26amp%3BType%3DMass&hash=4206aa596cd9b4e39cdcb8ec00c18960a80e0bdb), i found this Mass Spectrum of Hexanoic Acid online.
I know the peak at m/z=60 is due to a McLafferty fragmentation, but i can't really explain the peaks of m/z=87 and m/z=73.
Could someone please explain this to me?

Title: Re: Mass Spectrum of Hexanoic Acid
Post by: Babcock_Hall on December 09, 2017, 11:54:04 AM

A good place to start is to determine how much mass M^+• lost to make the those two fragments.

Title: Re: Mass Spectrum of Hexanoic Acid
Post by: Robin97 on December 10, 2017, 08:30:07 AM

Well according to the loss of the mass I would suggest a ethyl group is lost first (116-29=87) en then a methylene group is lost (87-14=73).
The problem is i can't really understand why that would happen, and what the mechanism is.
I always thought α-cleavages were more important if there is a carbonyl group present.

Title: Re: Mass Spectrum of Hexanoic Acid
Post by: Babcock_Hall on December 11, 2017, 08:53:36 AM

I was a little surprised also, but I consulted Silverstein et al, 4th ed., and they briefly discuss hexanoic acid on page 27.