Halogen bonding properties of 4-iodopyrazole and 4-bromopyrazole explored by rotational spectroscopy and ab initio calculations

Graham A. Cooper, Chris Medcraft, Josh D. Littlefair, Thomas J. Penfold, Nicholas R. Walker*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The combination of halogen- and hydrogen-bonding capabilities possessed by 4-bromopyrazole and 4-iodopyrazole has led to them being described as "magic bullets" for biochemical structure determination. Laser vaporisation was used to introduce each of these 4-halopyrazoles into an argon gas sample undergoing supersonic expansion prior to the recording of the rotational spectra of these molecules by chirped-pulse Fourier transform microwave spectroscopy. Data were obtained for four isotopologues of 4-bromopyrazole and two isotopologues of 4-iodopyrazole. Isotopic substitutions were achieved at the hydrogens attached to the pyrrolic nitrogen atoms of both 4-halopyrazoles and at the bromine atom of 4-bromopyrazole. The experimentally determined nuclear quadrupole coupling constants, χaa(X) and χbb (X)-χcc (X), of the halogen atoms (where X is the halogen atom) of each molecule are compared with the results of the ab initio calculations and those for a range of other halogen-containing molecules. It is concluded that each of 4-bromopyrazole and 4-iodopyrazole will form halogen bonds that are broadly comparable in strength to those formed by CH3X and CF3X.

Original languageEnglish
Article number214303
JournalJournal of Chemical Physics
Volume147
Issue number21
DOIs
Publication statusPublished - 7 Dec 2017

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