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Spectroscopy of Proton Coordination with Ethylenediamine.
- Source :
-
Journal of Physical Chemistry A . 6/14/2018, Vol. 122 Issue 23, p5168-5176. 9p. - Publication Year :
- 2018
-
Abstract
- Protonated ethylenediamine monomer, dimer, and trimer were produced in the gas phase by an electrical discharge/supersonic expansion of argon seeded with ethylenediamine (C2H8N2, en) vapor. Infrared spectra of these ions were measured in the region from 1000 to 4000 cm-1 using laser photodissociation and argon tagging. Computations at the CBS-QB3 level were performed to explore possible isomers and understand the infrared spectra. The protonated monomer exhibits a gauche conformation and an intramolecular hydrogen bond. Its parallel shared proton vibration occurs as a broad band around 2785 cm-1, despite the formally equivalent proton affinities of the two amino groups involved, which usually leads to low frequency bands. The barrier to intramolecular proton transfer is 2.2 kcal mol-1 and does not vanish upon addition of the zero-point energy, unlike the related protonated ammonia dimer. The structure of the dimer is formed by chelation of the monomer's NH3+ group, thereby localizing the excess proton and increasing the frequency of the intramolecular shared proton vibration to 3157 cm-1. Other highly fluxional dimer structures with facile intermolecular proton transfer and concomitant structural reorganization were computed to lie within 2 kcal mol-1 of the experimentally observed structure. The spectrum of the trimer is rather diffuse, and a clear assignment is not possible. However, an isomer with an intramolecular proton transfer like that of the monomer is most consistent with the experimental spectrum. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 10895639
- Volume :
- 122
- Issue :
- 23
- Database :
- Academic Search Index
- Journal :
- Journal of Physical Chemistry A
- Publication Type :
- Academic Journal
- Accession number :
- 139002883
- Full Text :
- https://doi.org/10.1021/acs.jpca.8b03592