INDO theoretical studies of 4-aminopyridine and protonated 4-aminopyridine
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 15,p. 1776-1778
- https://doi.org/10.1039/p29750001776
Abstract
Geometry optimized INDO calculations have been performed on 4-aminopyridine (2) and protonated 4-aminopyridine (1) in order to compare their optimized geometries, π-bond orders, C(4)–NH2 rotational barriers, charge densities, and π-electron distributions. It had previously been shown that 4-aminopyridine falls far off a linear correlation of ΔG° and ΔS° for the protonation equilibria of a series of 4-substituted pyridines. The calculations support the concept that a very high rotational barrier in (1) could cause this deviation. The contribution of a quinonoid resonance hybrid (1b) to (1) was greater than (2b) to (2). The π-cloud in (1) is polarized toward the ring nitrogen, relative to (2), and the C(4)–NH2 rotational barrier in (1)(27.3 kcal mol–1) is larger than in (2)(14.7 kcal mol–1).Keywords
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