FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY AND THEORETICAL-STUDIES OF GAS-PHASE S(N)2 NUCLEOPHILIC-SUBSTITUTION REACTIONS AT SP(3)-CARBON ATOMS

Gas phase S(N)2 intramolecular displacements are reported in which neu tral nucleophiles displace neutral leaving groups within cationic subs trates. In the intramolecular S(N)2 reaction of N-(2-piperidinoethyl)- 2,4,6-triphenylpyridinium cation (11), the cationic product 12 was det ected directly, Intramolecular reactions of -5,6,8,9-tetrahydro-7-phen yldibenzo[c,h]acridinium salts 13a-c, -5,6,8,9-tetrahydro-7-phenyldibe nzo[c,h]acridinium salt 14 and N-(omega-aminoalkyl)-2,4,6-triphenylpyr idinium salts 20a,b afforded the corresponding protonated acridinium c ation (15) or pyridinium cation (21) and, presumably, a neutral hetero cycle. This interpretation is supported by isotopic labeling control e xperiments. No evidence has been obtained for any intermolecular gas p hase S(N)2 reaction with a pyridine as leaving group; theoretical calc ulations suggest an explanation for these experimental results.