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The structures of liquid pyridine and naphthalene: the effects of heteroatoms and core size on aromatic interactions

Headen, TF; Cullen, PL; Patel, R; Taylor, A; Skipper, NT; (2018) The structures of liquid pyridine and naphthalene: the effects of heteroatoms and core size on aromatic interactions. Physical Chemistry Chemical Physics , 20 pp. 2704-2715. 10.1039/c7cp06689a. Green open access

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Abstract

Total neutron scattering has been used in conjunction with H/D and *N/15N isotopic substitution to determine the detailed liquid-state structures of pyridine and naphthalene. Analysis of the data via an empirical potential-based structure refinement method has allowed us to interrogate the full six-dimensional spatial and orientational correlation surfaces in these systems, and thereby to deduce the fundamental effects of a heteroatom and aromatic core-size on intermolecular π-π interactions. We find that the presence of a nitrogen heteroatom, and concomitant dipole moment, in pyridine induces surprisingly subtle departures from the structural correlations observed in liquid benzene: in both cases the most probable local motif is based on perpendicular (edge-to-face) intermolecular contacts, while parallel-displaced configurations give rise to a clear shoulder in the correlation surface. However, the effect of the heteroatom is revealed through detailed analysis of the intermolecular orientational correlations. This analysis shows a tendency for neighbouring pyridine molecules to direct one meta- and one para-hydrogen towards the neighbouring aromatic π-orbitals in edge-to-face configurations, while head-to-tail alignment of adjacent nitrogen atoms is favoured in face-to-face configurations. In contrast to this, increasing aromatic core size from one to only two rings has a clear and profound effect on the π-π interactions and liquid structure. Our experiments show that naphthalene-naphthalene contacts are dominated by parallel-displaced configurations, akin to those found in graphite. This marks a fundamental difference with the structure of liquid benzene, in which perpendicular geometries are favoured. Furthermore, it is remarkable to note that in the systems studied, the most favoured spatio-orientational configurations observed in the liquid state are not predicted from ab initio calculations and/or solid state crystallographic studies. This highlights the need for caution when extrapolating the results of crystallographic and computational studies to aromatic interactions in liquids and disordered systems.

Type: Article
Title: The structures of liquid pyridine and naphthalene: the effects of heteroatoms and core size on aromatic interactions
Location: England
Open access status: An open access version is available from UCL Discovery
DOI: 10.1039/c7cp06689a
Publisher version: http://doi.org/10.1039/c7cp06689a
Language: English
Additional information: Copyright © the Owner Societies 2017. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Cardiovascular Science
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Cardiovascular Science > Childrens Cardiovascular Disease
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10041796
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