QUANTUM COMPUTATIONAL STUDIES ON PORPHYCENE - Theoretical and Computational Research in the 21st Century - page 189

computed result supports the presence of two double bonds in pyrrol. The
π charge density at the P(1,5) is maximum, this observation clearly indi-
cates the presence of more electronegative element (nitrogen) in pyrrol.
Table 9.2(A) further reveals that the pair C-2 and C-3 has greater electron
density than other C pair.
The computed results in Tables 9.2(B) and (C) support the presence of
two double bonds in pyrrol.
The computed Fukui functions and local softnesses on the basis of
HMO calculation are presented in Table 9.6. An observation on the Table
9.6 reveals that the C-1 and C-4 are almost equal in their f + ( r ) and f − ( r )
values, the C-2 and C-3 centers are almost equal in their f + ( r ) and f − ( r )
value, the C-2 and C-3 have the lowest, and C-1andC-4 have the highest
f + ( r ) value, the N-5 has the lowest f − ( r ) value, and the pair C-1 and C-4 has
the highest f − ( r ) value.
It is also distinct from Table9.6 that the local softnesses of each atomic
sites of pyrrol follow the similar trend of variation as Fukui functions.
We are in a venture to study the Fukui function in the AM1 method
we have optimized in the planner structure of pyrrol in Argus lab software
to generate the eigen functions for the atomic sites of the molecule. The
computed results are presented in Table 9.8.
A deeper scrutiny of the Table 9.8 reveals that the f + (r) and f − ( r ) values
at the centers C-1 and C-5, C-2 and C-4 are almost the same. The centers
C-1 and C-5 have the lowest and the centers C-2 and C-4 have the highest
f + ( r ) value, and the centers C-2 and C-4 have the highest f − ( r ) value. The
center N-3 has the lowest f − ( r ) value.
It is distinct from Table 9.8 that the local softnesses of each atomic
sites of pyrrol follow the similar trend of variation like Fukui function.
We have computed the ZDO and Mulliken charge of the pyrrol mol-
ecule using the AM1 procedure and the computed results are presented in
Table 9.10.
An observation on Tables 9.6 and 9.8 reveals that on the basis of AM1
calculation, the Fukui function and local softness on the N atom is not the
maximum but from Table9.10 it is distinct that the charges on the N atom
are maximum in both ZDO and Mulliken method. The same observations
are also found (Table 9.2(a)) in case of HMO calculation where the Fukui
functions and local softness are not the maximum on the N atom, but on
some C atom that contradict the experimental observations. Thus, we may
point out that the Fukui function fails to predict the donor site of pyr-