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Electron impact (El), metastable ion (MI), and field ionization mass spectra of isomeric linear alkenes (C4-C8) are reported. In contrast to the identical MI and similar El spectra of these compounds, the FI spectra show pronounced differences in the fragmentation pattern. They are dominated by fragments due to allylic cleavage which allows an unequivocal location of the double bond. In general, allylic cleavage leads also to the most abundant fragment in branched double bond isomers although a few exceptions are observed with these compounds.

"he very complex isomerization patterns of methoxy and carbomethoxy substituted cydoalkanes (3-to 7-membered rings) have been investigated using coWmnal acíivation, metastable ion characterktics and ñeld ionization betics. Tlie extent of isomerization depends on both the ring size and the subtituent. Irrespective of the electronic properties of the substihient, ring opening involves exdusively the C-1-C-2 bond whereby linear dkene radical cations are formed. In the case of OCH, and COOCHJ substituents the position of the resuiting double bond (terminai or cu,B-onsaturated) is detennined more by the ring size of the precursor molecules and less by the electronic properties of the substituents. Contrary to these hdings auryi substituted cydoaikanes (3-to 5-membered h g s ) rearrange exdusively to tennmal dkene radical cations. The b d e r for double bond isomerization seems to be substantiaUiy intluenced by substihients.Unter Benutzung mehrerer Techniken, wie StoBaktivierung, Charaktenstik metastabiler Ionen und Feldionisationskinetik, wird das auBerst komplexe Isomerisierungsverhalten von methoxy-und carbomethoxysubstituierten Cycloalkanen (drei-bis siebengliedrige Ringe) analysiert. Das Ausmafj der Isomerisierung hangt sowohl von der Ringgrooe als auch vom Substituenten ab, wahrend die Ringoffnung unabhangig von den elektronischen Eigenschaften der Substituenten immer die C-1-C-2-Bindung betrifi. Hierbei werden ausschiiefjlich lineare Alken-Radikalkationen erzeugt. Bei OCH3-und COOCH,-Substituenten wird die Lage der resultierenden Doppelbindung (terminal oder a$-ungesattigt) hauptsachlich durch die RinggroBe des Cycloalkan-Molekülions und weniger durch den Substituenten beeinflufjt. Alkylsubstituierte Cycloalkane (drei-bis fünfgliedrige Ringe) lagern sich allerdings nur zu terminalen Alken-Radikalkationen um. Die Barriere der Doppelbindungswanderung scheint vom Substituenten abhangig zu sein.