Abstract
Eighteen pyridine-ring substituted
N
-benzyloxypyridinium cations all dissociate by two alternative pathways to give (A) a cation C
7
H
7
+
and the substituted pyridine 1-oxide, and (B) a cation C
7
H
7
O
+
and the substituted pyridine. Appearance potentials (
E
app
) have been measured for both pathways; they are higher by 3-17 kcal mol
-1
for the dominant pathway (A) than for (B).
The
E
app
values are compared with the Δ
H
f
values calculated by the AM1 method for reactants and products demonstrating extensive rearrangement in a product-like transition state (TS) for pathway (A) but not for (B). Both sets of
E
app
correlate roughly with Σσ for the pyridine ring substituents.
For the 4-dimethylamino derivatives, two additional homolytic pathways are found to give (C) a, cation Me
2
NC
5
H
4
NO
+
&z.rad; and (D) the 4-dimethylaminopyridine radical cation.