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Magnetic Properties and Aromaticity of o ‐, m ‐, and p ‐Benzyne
Author(s) -
De Proft Frank,
von Ragué Schleyer Paul,
van Lenthe Joop H.,
Stahl Frank,
Geerlings Paul
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020802)8:15<3402::aid-chem3402>3.0.co;2-6
Subject(s) - aromaticity , aryne , chemistry , chemical shift , benzene , computational chemistry , antiaromaticity , molecule , medicinal chemistry , organic chemistry
The relative aromaticities of the three singlet benzyne isomers, 1,2‐, 1,3‐, and 1,4‐didehydrobenzenes have been evaluated with a series of aromaticity indicators, including magnetic susceptibility anisotropies and exaltations, nucleus‐independent chemical shifts (NICS), and aromatic stabilization energies (all evaluated at the DFT level), as well as valence‐bond Pauling resonance energies. Most of the criteria point to the o ‐benzyne< m ‐benzyne< p ‐benzyne aromaticity order, whereas the relative aromaticity of each isomer with respect to benzene depends on the aromaticity criterion. An additional aromaticity evaluation involved the transition state of the Bergman cyclization of ( Z )‐hexa‐1,5‐diyn‐3‐ene which yields p ‐benzyne. Dissected NICS calculations reveal an aromatic transition state with a larger total NICS but a smaller NICS(π) component and thus lower aromaticity than benzene.