Heteroatomic substitution in aromatic σ biradicals: The six pyridynes

Christopher J. Cramer; Stefan Debbert

doi:10.1016/S0009-2614(98)00192-4

Heteroatomic substitution in aromatic σ biradicals: The six pyridynes

Christopher J. Cramer, Stefan Debbert

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Abstract

Interactions between the nitrogen lone pair and the biradical centers are weak in 3,4- and 3,5-pyridyne, but can be large enough in the remaining pyridynes (where at least one radical site is adjacent to nitrogen) to change singlet-triplet splittings by up to 19.6 kcal/mol compared to the corresponding benzynes. Singlet pyridynes having one dehydro site at the 2-position are stabilized relative to analogous benzynes because of increased contributions from zwitterionic resonance structures; this stabilization is not available to the triplets. Singlet-triplet splittings in the pyridynes and ¹H hyperfine couplings in the pyridyl radicals are well correlated.

Original language	English (US)
Pages (from-to)	320-326
Number of pages	7
Journal	Chemical Physics Letters
Volume	287
Issue number	3-4
DOIs	https://doi.org/10.1016/S0009-2614(98)00192-4
State	Published - May 1 1998

Bibliographical note

Funding Information:
We are grateful for high-performance vector and parallel computing resources made available by the Minnesota Supercomputer Institute and the University of Minnesota-IBM Shared Research Project, respectively. This work was supported in part by the National Science Foundation. Eric Patterson is thanked for research assistance.

Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.

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abstract = "Interactions between the nitrogen lone pair and the biradical centers are weak in 3,4- and 3,5-pyridyne, but can be large enough in the remaining pyridynes (where at least one radical site is adjacent to nitrogen) to change singlet-triplet splittings by up to 19.6 kcal/mol compared to the corresponding benzynes. Singlet pyridynes having one dehydro site at the 2-position are stabilized relative to analogous benzynes because of increased contributions from zwitterionic resonance structures; this stabilization is not available to the triplets. Singlet-triplet splittings in the pyridynes and 1H hyperfine couplings in the pyridyl radicals are well correlated.",

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AU - Debbert, Stefan

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N2 - Interactions between the nitrogen lone pair and the biradical centers are weak in 3,4- and 3,5-pyridyne, but can be large enough in the remaining pyridynes (where at least one radical site is adjacent to nitrogen) to change singlet-triplet splittings by up to 19.6 kcal/mol compared to the corresponding benzynes. Singlet pyridynes having one dehydro site at the 2-position are stabilized relative to analogous benzynes because of increased contributions from zwitterionic resonance structures; this stabilization is not available to the triplets. Singlet-triplet splittings in the pyridynes and 1H hyperfine couplings in the pyridyl radicals are well correlated.

AB - Interactions between the nitrogen lone pair and the biradical centers are weak in 3,4- and 3,5-pyridyne, but can be large enough in the remaining pyridynes (where at least one radical site is adjacent to nitrogen) to change singlet-triplet splittings by up to 19.6 kcal/mol compared to the corresponding benzynes. Singlet pyridynes having one dehydro site at the 2-position are stabilized relative to analogous benzynes because of increased contributions from zwitterionic resonance structures; this stabilization is not available to the triplets. Singlet-triplet splittings in the pyridynes and 1H hyperfine couplings in the pyridyl radicals are well correlated.

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Heteroatomic substitution in aromatic σ biradicals: The six pyridynes

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