EPOC
Table 1. Differences between the energies (in kcal mol-1) of H2S=NH2+ and +H3S=NH
calculated at selected semiempirical and ab initio levels
Level
-E a
Semiempirical
Level
-E a
MP2/6-311+G**//6-31G**
69.2
AM1
71.9
MP2/6-311+G(3df,2p)//6-31G**
56.8
PM3
34.7
DFT(B3LYP)/6-31G**//6-31G**
68.4
DFT(B3LYP)/6-311+G**//6-31G**
68.6
Ab initio
6-31G*//6-31G*
78.1
DFT(B3LYP)/6-311+G(3df,2p)//6-31G**
58.1
6-31G**//6-31G**
78.0
G1
67.4
MP2/6-31G*//6-31G*
70.2
G2
65.0
MP2/6-31G**//6-31G**
69.6
G2(MP2)
64.3
a E=E(H2S=NH2+)E(+H3S=NH) at 0 K calculated for the most stable structures: 3Hb and
3aH, except AM1 (3Ha and 3bH), and G (3Hd and 3aH); ZPE/6-31G* 0.6 kcal mol-1 and
ZPE/6-31G** 0.8 kcal mol-1 are included.
Table 2. Atomic properties of neutral and protonated moieties of thio derivative a
Structure
Property
3a
3b
3Hb
3aH
Total charge
N
q
V(rho)
Dipole
0
0
+1
+1
-1.535
523.2
0.538
-1.533
525.5
0.470
-1.318
390.8
0.171
-1.644
563.8
0.751
Energy
S
q
V(rho)
-54.959
-54.938
-54.899
-55.162
1.540
608.2
1.519
623.7
1.167
680.3
1.924
205.5
Dipole
Energy
H1 at S
q
V(rho)
1.539
-396.776
1.686
-396.786
1.210
-397.125
1.127
-396.555
-0.181
382.7
-0.176
375.8
0.069
333.1
0.041
369.8
Dipole
Energy
H2 at S
q
V(rho)
Dipole
Energy
H3 at N
q
V(rho)
0.036
-0.686
0.025
-0.692
0.028
-0.575
0.045
-0.593
-0.181
382.7
0.036
-0.686
-0.176
375.8
0.025
-0.692
0.069
333.1
0.028
-0.575
0.041
369.8
0.045
-0.593
0.359
223.5
0.366
214.0
0.506
177.5
0.536
176.9
Dipole
0.194
Energy
-0.483
H4
q
V(rho)
Dipole
Energy
a All values in atomic units.
0.193
-0.481
0.153
-0.401
at N
0.506
177.5
0.153
-0.401
0.148
-0.379
at S
0.103
335.4
0.028
-0.569
Table 3. Properties of bond critical points (BCP) in thio derivative moieties a
BPC
Property
S-H or N-H b
S-N
S-H
S-H
N-H
RHO
0.266
0.227
0.227
0.352
LAP
-0.052
-0.744
-0.744
-1.860
ellip
0.092
0.119
0.119
0.038
RHO
0.264
0.233
0.233
0.353
LAP
-0.131
-0.788
-0.788
-1.859
ellip
0.110
0.116
0.116
0.048
RHO
0.226
0.241
0.241
0.352
0.352
LAP
-0.515
-0.827
-0.827
-1.983
-1.983
ellip
0.164
0.053
0.053
0.044
0.044
RHO
0.293
0.246
0.246
0.341
0.254
LAP
0.356
-0.879
-0.879
-1.898
-0.948
ellip
0.212
0.027
0.027
0.017
0.038
3a
3b
3Hb
3aH
a All values in atomic units.
b In protonated structures.
Protonation of a given atom dramatically decreases its volume (Table 2). In the case of the S
atom its volume changes from more than 600 Bohr3 to ca. 205 Bohr3 (1 Bohr=0.52918 Å).
Similarly for the N atom, its volume on protonation decreases from ca. 525 Bohr3 to 390
Bohr3. In the cations, also all H atoms have a bit smaller volumes – usually the difference
amounts from a few Bohr(s)3 to more than 30 Bohr3.
There are also interesting changes of atomic dipoles. Protonation at S increases the
dipole moment at N atom and decreases the dipole moment of S. It does not influence much
the dipole moments of hydrogens. For the N-protonation both dipoles at the heteroatoms are
decreased. This is due to more symmetric distribution of electron density in this case.
Similar trends are also observed for atomic energy. On protonation, the energy of the S
atom (protonation site) increases ca. 0.22 Hartree compared to the energy of the same atom in
neutral 3a or 3b and ca. 0.55 Hartree compared to the energy of S in the other protonated
species. Similar situation happens for the N and H atoms with the largest changes at the
hydrogens attached to the sulphur atom (ca. 0.1 Hartree). The amount of charge at the bond
CP’s is in the range from ca. 0.22 for S-H bonds to 0.35 for N-H (Table 3). For the SN bond,
one gets almost ionic situation for 3aH (with CP in the region of a positive laplacian) as a
result of the S-protonation and more covalent bond (with negative laplacian) for the Nprotonation (rho equal to 0.29 and 0.22 for 3aH and 3Hb, respectively). And again in the case
of neutral molecules the charge and laplacian at the bond CPs are in-between the values for
the S- and N-protonations. The SN bond has a significant double character in 3aH and is more
symmetric – more singular - in 3Hb and the most symmetric in the neutral isomers.
Ellipticities characterize degree of double character of bonds. They are quite small for all
bonds. The largest ellipticity is for the SN bond in 3aH. It is accompanied by smaller
ellipticities of the singular bonds in this compound. Quite a reverse situation is for the other
molecules (3a, 3b, 3Hb).
Table 4. Energies of protonation (in kcal mol-1) calculated at selected ab initio levels for the
most stable structures of HiX=NH (X=C, N, S or P, i=1, 2 or 3)
-Eprot a
HN=NH b
H2C=NH c
H2S=NH d
H3P=NH e
6-31G*//6-31G*
6-31G**//6-31G**
MP2/6-31G*//6-31G*
186.1
189.2
182.1
213.1
215.8
207.0
231.5
234.1
224.7
238.2
241.0
230.6
MP2/6-31G**//6-31G**
MP2/6-311+G**//6-31G**
MP2/6-311+G(3df,2p)//6-31G**
DFT(B3LYP)/6-31G**//6-31G**
186.7
181.8
180.6
186.6
211.0
205.4
204.0
210.3
228.7
225.1
214.2
227.0
234.7
231.0
223.2
232.6
Level
DFT(B3LYP)/6-311+G**//6-31G**
181.8
205.7
221.6
229.0
DFT/6-311+G(3df,2p)//6-31G**
182.5
205.6
215.8
225.1
G1
182.7
205.5
224.6
227.0
a Eprot=E(BH+)-E(B) at 0 K; ZPE=ZPE(BH+)-ZPE(B) is included.
b For 2b+H+2H; ZPE at both the HF/6-31G* and HF/6-31G** levels is 9.2 kcal mol-1.
c For 1+H+1H; ZPE at both the HF/6-31G* and HF/6-31G** levels is 9.5 kcal mol-1.
d For 3a+H+3Hb; ZPE at the HF/6-31G* level is 8.6 kcal mol-1, and at the HF/6-31G**
level is 8.5 kcal mol-1.
e For 4a+H+4Hb; ZPE at both the HF/6-31G* and HF/6-31G** levels is 8.7 kcal mol-1.
Table 5. Differences in Eprot as a fuction of calculational procedure and of basis set applied
and replacement of X-atom in nitrogen bases HiX=NH (in kcal mol-1)
-Eprot a
Level
HN=NH
H2S=NH
H3P=NH
Semiempirical
AM1
PM3
-28.9
-21.3
14.8
18.4
26.1
48.0
Ab initio
6-31G*//6-31G*
6-31G**//6-31G**
MP2/6-31G*//6-31G*
-27.0
-26.6
-24.9
18.4
18.3
17.7
25.1
25.6
24.0
MP2/6-31G**//6-31G**
MP2/6-311+G**//6-31G**
MP2/6-311+G(3df,2p)//6-31G**
DFT(B3LYP)/6-31G**//6-31G**
DFT(B3LYP)/6-311+G**//6-31G**
-24.3
-23.6
-23.4
-23.7
-23.9
17.7
19.7
10.2
14.7
15.9
24.1
26.0
19.6
22.7
23.7
DFT(B3LYP)/6-311+G(3df,2p)//6-31G**
G1
a Eprot=Eprot(HiX=NH)-Eprot(H2C=NH).
-23.1
-22.8
10.2
19.1
19.9
21.5