13482-26-3Relevant academic research and scientific papers
Direct evidence for anchimeric assistance in alcohol elimination from gas-phase MH+ ions of 1,4-dialkoxycyclohexanes under chemical ionisation. Experiment and theory
Shvily, Ronit,Mueller, Thomas,Apeloig, Yitzhak,Mandelbaum, Asher
, p. 1221 - 1234 (2007/10/03)
trans-1,4-Dialkoxycyclohexanes afford very abundant [MH - ROH]+ ions upon chemical ionisation (CI), in contrast to the cis-isomers, suggesting anchimeric assistance in the alcohol elimination from the MH+ ions of the trans-diethers. Collision induced dissociation (CID) measurements of the [MH - ROH]+ ions, obtained from various suitably deuterium labelled stereoisomeric 1-ethoxy-4-methoxycyclohexanes, indicated fromation of symmetrical bicyclic ethyl and methyl oxonium ions by an anchimerically assisted alcohol elimination from the trans-diethers. On the other hand these measurements suggest that the cis-isomers afford isomeric monocyclic O-protonated 4-alkoxycyclohexene cations, in which the hydrogens at positions 2 and 3 (as well as those at positions 5 and 6, and 1 and 4) are not equivalent. The two results, namely the symmetrical bicyclic structure and the high abundance of the [MH - ROH]+ ions in the CI mass spectra of the trans-diethers, in contrast to the non-symmetrical monocyclic structure and low abundance of these ions in the cis-isomers, are suggested to be direct evidence for anchimeric assistance in a gas-phase ion dissociation process. Ab initio calculations at the MP3/6-31G*//6-31G* level support the anchimerically assisted elimination mechanism observed in trans-1-ethoxy-4-methoxycyclohexane, but also show that the energy difference between the anchimerically assisted and non-assisted elimination mechanisms is small (ca. 2-3 kcal mol-1)(1 cal = 4.184 J).
The mechanism of methanol loss from the (M-H) ions of cis- And trans-4-methoxycyclohexanol. the application of experiment and theory in concert
Dua, Suresh,Buntine, Mark A.,Raftery, Mark J.,Eichinger, Peter C. H.,Bowie, John H.
, p. 2489 - 2496 (2007/10/03)
Deprotonation of cis- and trans-4-methoxycyclohexanol by HO- in the ion source of a mass spectrometer yields the (M - H)- alkoxide ions exclusively. Both of these ions, on collisional activation, form MeO-, MeO-(H2O) and eliminate MeOH. The loss of methanol forms the base peak of the spectrum, and the structure of this daughter anion is shown to be the alkoxide ion from cyclohex-3-enol for both isomers. Evidence (based on product ion, deuterium labelling and AMI semiempirical computational studies) indicates that the loss of methanol from the trans isomer proceeds by an internal SN2 cyclisation of O- at the four position (through a 1,4-epoxycyclohexane species) followed by 3,4 elimination. A similar sequence may occur for the cis-isomer, but in this case the process is not as energetically favourable as that for the trans isomer.
