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Hei and heii spectra of 3‐halopyridines
Author(s) -
Xue Jing,
Hughes Jason M.,
Von NagyFelsobuki Ellak I.
Publication year - 1996
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570330634
Subject(s) - chemistry , spectral line , bromine , ab initio , molecule , ionization , sequence (biology) , ultraviolet , halogen , simple (philosophy) , computational chemistry , lone pair , crystallography , analytical chemistry (journal) , ion , organic chemistry , physics , alkyl , quantum mechanics , astronomy , philosophy , epistemology , biochemistry
The ultraviolet photoelectron spectra (UPS) of 3‐fluoro‐, 3‐ chloro‐, 3‐bromo‐ and 3‐ iodopyridine were recorded and interpreted using a composite‐molecule model. The sequence of the four lowest ionization energies for 3‐fluoro‐ and 3‐chloropyridine is: π 3 (1a 2 ) < n N (11a 1 )ππ 2 (2b 1 )π∼ pyr (7b 2 ), whereas for 3‐bromo‐ and 3‐iodopyridine the assignment is: π 3 (1a 2 ) ‐ π x πn N (11a 1 )πσ x π 2 (2b 1 ) (where X represents a bromine or iodine lone‐pair). Comparison of the HeI and HeII band intensities and correlations with the UPS assignment of the 2‐halopyridines confirm this sequence. However, ab initio calculations using the STO‐3G*//STO‐3G* and 6–31G**//STO‐3G* models do not agree with either the composite‐molecule model, simple UPS correlations and HeI/HeII cross‐section ratios. For 3‐fluoropyridine, the HAM/3 model was in agreement with the proposed assignment.