ISSN:
0894-3230
Schlagwort(e):
Organic Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
Zusätzliches Material:
2 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/poc.610030207
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