10.1021/acs.joc.5b02499.s001
Milovan Stojanović
Milovan
Stojanović
Marija Baranac-Stojanović
Marija
Baranac-Stojanović
Aromaticity of Diazaborines
and Their Protonated Forms
American Chemical Society
2016
azaborine
BN
protonation change aromaticity
CH ortho
HOMA
diazaborine
CH group
cyclic delocalization
PDI
ECRE
NICS
Aromaticity
2016-01-04 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Aromaticity_of_Diazaborines_and_Their_Protonated_Forms/2092729
Substitution of a CH group in benzene
with nitrogen has a little
effect on its aromaticity (Wang et al., <i>Org. Lett.</i> <b>2010</b>, <i>12</i>, 4824). How does the same
type of substitution affect aromatic character of the three isomeric
azaborines? Does further protonation change aromaticity of diazaborines?
This work is aimed at answering these questions. Such a knowledge
should be of interest for further exploration and application of BN/CC
isosterism. Aromaticity of diazaborines and their protonated forms
is studied with the aid of four aromaticity indices, HOMA, NICS(0)<sub>πzz</sub>, PDI and ECRE. Generally, NICS(0)<sub>πzz</sub> and PDI point to similar aromaticity of diazaborines and their parent
azaborines, while HOMA and ECRE indicate some changes. Thus, aromaticity
of 1,2-azaborine slightly decreases/increases when CH <i>meta</i>/<i>ortho</i>,<i>para</i> to B is substituted
with nitrogen. Aromaticity of the most aromatic 1,3-azaborine remains
almost unchanged when CH <i>meta</i> to B and N is replaced
with nitrogen, and becomes slightly weaker when any other CH group
is substituted with nitrogen. Replacement of the CH <i>ortho</i> to N in 1,4-azaborine does not change much its cyclic delocalization,
while replacement of the CH <i>ortho</i> to B leads to smaller
cyclic delocalization. Protonated forms are either of similar or decreased
aromaticity compared with neutral molecules.