Dissociation Reactions of Low-Energy Pentenyl Methyl Ether Radical Cations C ₅ H ₉ OCH ₃ ^•+

The dissociation chemistry of the low-energy C 5 H 9 OCH 3 •+ ions generated from the 13 isomeric pentenyl methyl ethers derived from stable alkenols has been studied. This was done by examining their metastable ion characteristics, in conjunction with 2 H and 13 C-labelling as well as collision-induced dissociation and neutralisation–reionisation experiments. The influence of the position and substitution pattern of the double bond on the chemistry of these C 6 H 12 O •+ species is considered. The closely similar reactions of C 2 H 5 CH=CHCH 2 OCH 3 •+ , 3 •+ , CH 2 =CH–CH(C 2 H 5 )OCH 3 •+ , 4 •+ , and CH 2 =C(C 2 H 5 )CH 2 OCH 3 •+ , 13 •+ , point to a common chemistry, which is rationalised in terms of facile 1,2-H and 1,2-C 2 H 5 shifts via distonic ions. Each of the other isomers displays a distinct, though often related, chemistry. The eight allylic ionised ethers easily lose CH 3 • to produce C 5 H 9 O + oxonium ions, whose structure was established by CID experiments; ions 3 •+ / 4 •+ / 13 •+ also readily expel C 2 H 5 • to give C 4 H 7 O + ions of structure CH 2 =CH–C + (H)OCH 3 . Elimination of CH 3 OH is also significant for 3 •+ / 4 •+ / 13 •+ and for (CH 3 ) 2 C=CHCH 2 OCH 3 •+ , 8 •+ , and CH 3 CH=C(CH 3 )CH 2 OCH 3 •+ , 11 •+ . Besides expelling CH 3 • and/or C 2 H 5 • and CH 3 OH, the three homoallylic isomers undergo dissociations which are (almost) absent for their allylic counterparts: thus, both CH 3 CH=CH(CH 2 ) 2 OCH 3 •+ , 2 •+ , and CH 2 =CH–CH(CH 3 )CH 2 OCH 3 •+ , 10 •+ , lose H • and H 2 O, whereas CH 2 =C(CH 3 )CH 2 CH 2 OCH 3 •+ , 7 •+ , is unique in predominantly losing CH 2 O. For the losses of CH 2 O and H 2 O mechanisms are proposed in which ion–neutral complexes of the type [C 5 H 10 •+ / CH 2 O] and [C 6 H 10 •+ / H 2 O] are key intermediates. The behaviour of the non-(homo)allylic isomer, CH 2 =CH(CH 2 ) 3 OCH 3 •+ , 1 •+ , is similar to that of 2 •+ but the reactions occur in different proportions. A mechanism for the facile loss of an alkyl radical from 1 + is proposed in which 1,4-H shifts and distonic ions as well as communication with ionised cyclopentyl methyl ether, 14 •+ , play an important role.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.