A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine

Thais Scott, Reed Nieman, Adam Luxon, Boyi Zhang, Hans Lischka, Laura Gagliardi, Carol A. Parish

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Three diradical pyrazine isomers were characterized using highly correlated, multireference methods. The lowest lying singlet and triplet state geometries of 2,3-didehydropyrazine (ortho), 2,5-didehydropyrazine (para), and 2,6-didehydropyrazine (meta) were determined. Two active reference spaces were utilized. The complete active space (CAS) (8,8) includes the σ and σ∗ orbitals on the dehydrocarbon atoms as well as the valence π and π∗ orbitals. The CAS (12,10) reference space includes two additional orbitals corresponding to the in-phase and out-of-phase nitrogen lone pair orbitals. Adiabatic and vertical gaps between the lowest lying singlet and triplet states, optimized geometries, canonicalized orbital energies, unpaired electron densities, and spin polarization effects were compared. We find that the singlet states of each diradical isomer contain two significantly weighted configurations, and the larger active space is necessary for the proper physical characterization of both the singlet and triplet states. The singlet-triplet splitting is very small for the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers (+1.8 and -1.4 kcal/mol, respectively) and significant for the 2,5-didehydropyrazine (para) isomer (+28.2 kcal/mol). Singlet geometries show through-space interactions between the dehydocarbon atoms in the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers. An analysis of the effectively unpaired electrons suggests that the 2,5-didehydropyrazine (para) isomer also displays through-bond coupling between the diradical electrons.

Original languageEnglish (US)
Pages (from-to)2049-2057
Number of pages9
JournalJournal of Physical Chemistry A
Volume123
Issue number10
DOIs
StatePublished - Mar 14 2019

Fingerprint

Pyrazines
pyrazines
Isomers
isomers
orbitals
atomic energy levels
Geometry
geometry
Atoms
Spin polarization
Electrons
electron spin
Carrier concentration
atoms
electrons
Nitrogen
valence
nitrogen
polarization
configurations

PubMed: MeSH publication types

  • Journal Article

Cite this

Scott, T., Nieman, R., Luxon, A., Zhang, B., Lischka, H., Gagliardi, L., & Parish, C. A. (2019). A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine. Journal of Physical Chemistry A, 123(10), 2049-2057. https://doi.org/10.1021/acs.jpca.8b12440

A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine. / Scott, Thais; Nieman, Reed; Luxon, Adam; Zhang, Boyi; Lischka, Hans; Gagliardi, Laura; Parish, Carol A.

In: Journal of Physical Chemistry A, Vol. 123, No. 10, 14.03.2019, p. 2049-2057.

Research output: Contribution to journalArticle

Scott, T, Nieman, R, Luxon, A, Zhang, B, Lischka, H, Gagliardi, L & Parish, CA 2019, 'A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine', Journal of Physical Chemistry A, vol. 123, no. 10, pp. 2049-2057. https://doi.org/10.1021/acs.jpca.8b12440
Scott, Thais ; Nieman, Reed ; Luxon, Adam ; Zhang, Boyi ; Lischka, Hans ; Gagliardi, Laura ; Parish, Carol A. / A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine. In: Journal of Physical Chemistry A. 2019 ; Vol. 123, No. 10. pp. 2049-2057.
@article{dcfd2bc5a185474399ca8576e2b2de4a,
title = "A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine",
abstract = "Three diradical pyrazine isomers were characterized using highly correlated, multireference methods. The lowest lying singlet and triplet state geometries of 2,3-didehydropyrazine (ortho), 2,5-didehydropyrazine (para), and 2,6-didehydropyrazine (meta) were determined. Two active reference spaces were utilized. The complete active space (CAS) (8,8) includes the σ and σ∗ orbitals on the dehydrocarbon atoms as well as the valence π and π∗ orbitals. The CAS (12,10) reference space includes two additional orbitals corresponding to the in-phase and out-of-phase nitrogen lone pair orbitals. Adiabatic and vertical gaps between the lowest lying singlet and triplet states, optimized geometries, canonicalized orbital energies, unpaired electron densities, and spin polarization effects were compared. We find that the singlet states of each diradical isomer contain two significantly weighted configurations, and the larger active space is necessary for the proper physical characterization of both the singlet and triplet states. The singlet-triplet splitting is very small for the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers (+1.8 and -1.4 kcal/mol, respectively) and significant for the 2,5-didehydropyrazine (para) isomer (+28.2 kcal/mol). Singlet geometries show through-space interactions between the dehydocarbon atoms in the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers. An analysis of the effectively unpaired electrons suggests that the 2,5-didehydropyrazine (para) isomer also displays through-bond coupling between the diradical electrons.",
author = "Thais Scott and Reed Nieman and Adam Luxon and Boyi Zhang and Hans Lischka and Laura Gagliardi and Parish, {Carol A.}",
year = "2019",
month = "3",
day = "14",
doi = "10.1021/acs.jpca.8b12440",
language = "English (US)",
volume = "123",
pages = "2049--2057",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "10",

}

TY - JOUR

T1 - A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine

AU - Scott, Thais

AU - Nieman, Reed

AU - Luxon, Adam

AU - Zhang, Boyi

AU - Lischka, Hans

AU - Gagliardi, Laura

AU - Parish, Carol A.

PY - 2019/3/14

Y1 - 2019/3/14

N2 - Three diradical pyrazine isomers were characterized using highly correlated, multireference methods. The lowest lying singlet and triplet state geometries of 2,3-didehydropyrazine (ortho), 2,5-didehydropyrazine (para), and 2,6-didehydropyrazine (meta) were determined. Two active reference spaces were utilized. The complete active space (CAS) (8,8) includes the σ and σ∗ orbitals on the dehydrocarbon atoms as well as the valence π and π∗ orbitals. The CAS (12,10) reference space includes two additional orbitals corresponding to the in-phase and out-of-phase nitrogen lone pair orbitals. Adiabatic and vertical gaps between the lowest lying singlet and triplet states, optimized geometries, canonicalized orbital energies, unpaired electron densities, and spin polarization effects were compared. We find that the singlet states of each diradical isomer contain two significantly weighted configurations, and the larger active space is necessary for the proper physical characterization of both the singlet and triplet states. The singlet-triplet splitting is very small for the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers (+1.8 and -1.4 kcal/mol, respectively) and significant for the 2,5-didehydropyrazine (para) isomer (+28.2 kcal/mol). Singlet geometries show through-space interactions between the dehydocarbon atoms in the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers. An analysis of the effectively unpaired electrons suggests that the 2,5-didehydropyrazine (para) isomer also displays through-bond coupling between the diradical electrons.

AB - Three diradical pyrazine isomers were characterized using highly correlated, multireference methods. The lowest lying singlet and triplet state geometries of 2,3-didehydropyrazine (ortho), 2,5-didehydropyrazine (para), and 2,6-didehydropyrazine (meta) were determined. Two active reference spaces were utilized. The complete active space (CAS) (8,8) includes the σ and σ∗ orbitals on the dehydrocarbon atoms as well as the valence π and π∗ orbitals. The CAS (12,10) reference space includes two additional orbitals corresponding to the in-phase and out-of-phase nitrogen lone pair orbitals. Adiabatic and vertical gaps between the lowest lying singlet and triplet states, optimized geometries, canonicalized orbital energies, unpaired electron densities, and spin polarization effects were compared. We find that the singlet states of each diradical isomer contain two significantly weighted configurations, and the larger active space is necessary for the proper physical characterization of both the singlet and triplet states. The singlet-triplet splitting is very small for the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers (+1.8 and -1.4 kcal/mol, respectively) and significant for the 2,5-didehydropyrazine (para) isomer (+28.2 kcal/mol). Singlet geometries show through-space interactions between the dehydocarbon atoms in the 2,3-didehydropyrazine (ortho) and 2,6-didehydropyrazine (meta) isomers. An analysis of the effectively unpaired electrons suggests that the 2,5-didehydropyrazine (para) isomer also displays through-bond coupling between the diradical electrons.

UR - http://www.scopus.com/inward/record.url?scp=85062882619&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85062882619&partnerID=8YFLogxK

U2 - 10.1021/acs.jpca.8b12440

DO - 10.1021/acs.jpca.8b12440

M3 - Article

VL - 123

SP - 2049

EP - 2057

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 10

ER -