Undergraduate Research Journal

The Audier-Stevenson Rule: 2,6-dimethyl-2-heptene
Howard Park 1 , Thomas H. Morton 2
1
Department of Biology
2
Department of Chemistry
University of California, Riverside
ABSTRACT
In electron ionization mass spectrometry a gaseous molecule is fragmented by the introduction
of a high energy electron. According to the Audier-Stevenson Rule it is expected that the
fragmentation species of highest stability produces a higher intensity peak on a mass spectrum.
However, there is an apparent violation of the Audier-Stevenson Rule when comparing the m/z
69 and m/z 57 fragmentations for 2,6-dimethyl-2-heptene. The lowest energy fragments for an
m/z 57 split are more stable than the fragments for the m/z 69 split; yet the mass spectrum shows
the m/z 69 peak to be more intense. Herein, we propose an explanation, which takes into account
the preferred conformation of the 2,6-dimethyl-2-heptene starting material. In conclusion, the
Audier-Stevenson Rule was not contradicted.
FACULTY Mentor
Thomas H. Morton
Department of Chemistry
Tom Morton has been on UCR’s chemistry faculty for more than 30 years. He teaches large lecture
courses of undergraduate chemistry; and in 2006, initiated University Honors discussion sections
for organic chemistry. In these discussion sections each student performs an original computational
investigation. While all the CHEM122H students in Fall 2011 discovered important aspects of
thermodynamic versus kinetic control in mass spectrometric decompositions, Howard Park took the
opportunity to investigate more deeply the branching between two competing pathways for breaking
a single C-C bond, consulting the chemical research literature to propose an explanation as to why
the favored fragmentation yields an allylic cation. His effort presents a new insight into unimolecular
dissociation and puts forth a hypothesis that can be tested experimentally. This work was supported
in part by NSF grant CHE0848517.
A U T H O R
Howard Park
Biology
Howard Park is a second year University
Honors student majoring in Biology. With
plans to attend medical school, Howard
participates in the Critical Care Volunteer
Program at Riverside Community
Hospital in order to gain experience with
patient care and help out within the local
community. He strives to excel in all of
his science classes; and with this article,
his first published academic paper, furthered
his understanding of Organic
Chemistry. Howard extends many thanks
to Professor Thomas Morton for his mentorship
and Lisa Sarigiani for her writing
consultation.
U C R U n d e r g r a d u a t e R e s e a r c h J o u r n a l 1 9