Chemistry Reference
In-Depth Information
hydroxyl groups and
electrons of the aromatic rings takes place (Avram
1994
,
Chap. 19). Using the Streitwieser parameters (Table
11.7
) standardized based on ex-
perimental results using computational technique (of the secular determinant and its
diagonalization on the irreducible representations of the symmetry group associated
to the corresponding molecules) results allowing the correlation with their chemical
reactivity have been obtained.
The presence of the (
π
SO
3
H) group does not disturb the electronic state of the
carbon atom to which it is linked and it does not participate in conjugation with the
aromatic ring (Streitwieser
1961
).
The delocalization energy (DE),
−
ε
LUMO
enable the estimation of
aromaticity, reducing or oxidizing character of these compounds (Table
11.12
).
Regarding the absorption bands in visible and ultraviolet domains, the first band
(
λ
max
) corresponds to either the transition between
ε
HOMO
and
ε
HOMO
of the large
conjugated system or the transition from a non participating atomic orbital to
ε
LUMO
and
ε
LUMO
(Simon
1973
, Chap. 2,
1964
).
The internal consistency of the data in Table
11.12
is checked with the following
relationship by determining the resonance integral parameter for each analyzed sys-
tem obtaining the results reported in the last column of Table
11.12
. Their striking
similarity proves the reliability of the used data and the undertaken calculations.
2
πc
h
¯
β
[
eV
]
=
(11.66)
λ
[
ε
LUMO
(
β
)
−
ε
HOMO
(
β
)]
Moreover, the common value
β
55
.
0819 kcal/mol predicts the
localization of this constant for cyclic aromatic systems under the range of linear
polyenes, of approximately
=−
2
.
3877 eV
=−
70 kcal/mol.
The obtained results lead us to the following hierarchy on the chemical reactivity
of the eight hydroxyl arenes:
−
60 kcal/mol,
−
According with
ε
HOMO
and
ε
LUMO
values, the C
10
H
7
OH compounds show superior
tendency to oxidation or reduction processes than the corresponding C
6
H
5
OH
π —
systems. Unlike the more stable phenol, the less aromatic naphthols participate
in some chemical reactions under tautomeric form (Avram
1994
, Chap. 19).
Phenol (I), more reactive than benzene (DE
8
β
) (Simon
1973
, Chap. 2), is
more sensitive against oxidazing agents (FeCl
3
). It easily participates at reactions
with SE mechanisms. In contrast to the (II-VIII) compounds, it does not present
prototropic tautomerism (Nenitzescu
1966
, Part II, Chap. 2).
=
Our calculations are consistent with the physico-chemical behavior of diphenols.
Thus, 1,2-dihydroxy phenol (II) with 1,2-benzoquinone form an electrochemi-
cally reversible redox system. The value of the quinone redox potential is small,
therefore this compound is a strong oxidant and consequently the corresponding
diphenol is a weaker reductant (Avram
1995
, Chap. 25). However, the diphenol
is oxidated by the ammoniacal solution of silver at low temperature and by the
Fehling reagent at high temperature, while 1,3-dihydroxy phenol (III) only reacts
with the Tollens reagent at high temperature (Nenitzescu
1966
, Part II, Chap. 2).
