Molecules 2004, 9(10), 830-841; doi:10.3390/91000830
Article

Electron-Induced (EI) Mass Fragmentation is Directed by Intra- molecular H-Bonding in Two Isomeric Benzodipyran Systems

1 Department of Pharmaceutical Sciences, Texas Tech University Health Sciences Center, School of Pharmacy, Amarillo, TX 79106, USA 2 School of Pharmacy, North West University, Potchefstroom 2520, South Africa 3 Research and Development, Lab Water Division, Millipore, St Quentin-Yvelines, France
* Author to whom correspondence should be addressed.
Received: 30 March 2004; Accepted: 29 July 2004 / Published: 30 September 2004
PDF Full-text Download PDF Full-Text [270 KB, uploaded 20 June 2008 16:51 CEST]
Abstract: The striking differences observed in the electron-induced (EI) mass fragmentationpathways of two isomeric benzodipyrans are attributable to hydrogen bonding in thesemolecules. In the "angular" isomer, 6-butyryl-5-hydroxy-2,2,8,8-tetramethyl-3,4,9,10-tetra-hydro-2H,8H-benzo[1,2-b:3,4-b1]dipyran (2), H-bonding occurs between the aromatic OHgroup and the alpha carbonyl moiety contained in the ortho-phenone group, whereas in the"linear" isomer, 10-butyryl-5-hydroxy-2,2,8,8-tetramethyl-3,4,6,7-tetrahydro-2H,8H-benzo-[1,2-b:5,4-b1]dipyran (3), the aromatic OH group is para to the phenone moiety, effectivelyprecluding any H-bonding. Semi-empirical molecular orbital calculations (AM1) were used tocompare predicted sites of ionization with associated fragmentation patterns. In bothmolecules, the highest occupied molecular orbital (HOMO) was located predominantly on thearomatic moiety. Similarly, in the radical cation species of both compounds, maximum spindensity was located over the aromatic rings. Neither the HOMO nor the spin density mapsprovided a rational explanation for the differences in fragmentation patterns of the twobenzodipyran isomers. The H-bonding favors EI alpha aromatic ring C-O bond cleavage in the"angular" benzodipyran and in 5,7-dihydroxy-2,2-dimethyl-8-butyryl chroman (1), a relatedmonochroman also containing a hydrogen proximal to the aromatic ring C-O bond. In contrast,fragmentation of the "linear" benzodipyran followed a different route, which was exhibited byits base peak resulting from the loss of a propyl group from the butyryl side-chain.
Keywords: benzodipyrans; hydrogen-bond directed mass fragmentation; EIMS.

Article Statistics

Load and display the download statistics.

Citations to this Article

Cite This Article

MDPI and ACS Style

Van der Schyf, C.J.; Mabic, S. Electron-Induced (EI) Mass Fragmentation is Directed by Intra- molecular H-Bonding in Two Isomeric Benzodipyran Systems. Molecules 2004, 9, 830-841.

AMA Style

Van der Schyf CJ, Mabic S. Electron-Induced (EI) Mass Fragmentation is Directed by Intra- molecular H-Bonding in Two Isomeric Benzodipyran Systems. Molecules. 2004; 9(10):830-841.

Chicago/Turabian Style

Van der Schyf, Cornelis J.; Mabic, Stéphane. 2004. "Electron-Induced (EI) Mass Fragmentation is Directed by Intra- molecular H-Bonding in Two Isomeric Benzodipyran Systems." Molecules 9, no. 10: 830-841.

Molecules EISSN 1420-3049 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert