Studies in Organic Mass Spectrometry III 1, 3‐Cyclohexanediones

Abstract

The mass spectra of 1,3-cyclohexanedione and its 2, 4 and 5 substituted derivatives are discussed.Most fragmentation patterns can be rationalised starting from the diketo form, through initial 1.2 and 1.6 bond cleavages. Evidence is advanced that ionised enol-molecules mainly yield retro Diels-Alder type degradations. Ring bond cleavage processes are strongly dependent on the position and size of the substituents.The mass-spectral behaviour of acyclic 1,3-diketones has been discussed recently (293). We have now studied the fragmentation upon electron impact of 1,3-cyclohexanediones.The only mass spectra of the latter class of compounds which have been discussed are those of dimedone (IX) and 2-ethyldimedone ( 5, (XI).For the interpretation of the mass spectra, the two different initial a cleavages (1,2 and 1,6 bonds) have to be taken in account; each leading to two distinct groups of fragmentation patterns. The relative importance of the two different cleavages is dependent on additional substitution in the 2-or 6-positions, resulting in variation in stability of the two bonds involved. However, like in 1,3 acylic diketones (3) enol-forms give a different fragmentation than the diketo-forms, although this influence of keto-enol tautomerism is less straightforward for the cyclic 1,3-diketones under

The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products

“…In both tables, the first column refers to the designation used in the fragmentation schemes. As already mentioned by Vandewalle et al (15,16), relative abundances of the signals in the EI spectra of 2,5-dialkylcyclohexan-1,3-diones strongly depend on the substituents, and spectra may be different after excitation of either the diketo or the enol structures. According to our investigations, some signals observed in low resolution represent fragments of at least two different atomic compositions.…”

“…Basic investigations have been carried out by Vandewalle et al (15,16), whereas Goto et al (17) and Maquestiau and Lejeune (18) focused on spectra of dimedone derivatives. Therefore, it appeared highly desirable to better understand the mass spectrometric fragmentation pattern of chiloglottone1 and its analogs to identify respective diagnostic ions and, thus, facilitate structure elucidation of other volatiles representing this new type of compound in nature.…”

Tautomerism: Introduction, History, and Recent Developments in Experimental and Theoretical Methods

“…According to Kol'tsov and Kheifets [55], the first study in which NMR was employed to investigate tautomerism was published in 1953 [56]. Although mass spectrometry is not related to solution, we have to recognize the first attempts (in 1967) devoted to its application in the structural study of tautomeric compounds [57].…”

Studies in organic mass spectrometry. XVII The fragmentation of methyl enol ethers of 1,3‐cyclohexanediones and 1,3‐cyclopentanediones

“…153 (9) 153 ( 4 ) ----125 (6) 125 (3) 125 ( Relative intensities between brackets. Table 2 : 2-butyl-3-methoxy-2-cyclohexenone and its deuterated homologues…”