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The electronic structure and nonplanarity of cyanamide
Journal of Molecular
Structure
285
Elsevier Publishing Company, Amsterdam. Printed in the Netherlands
THE ELECTRONIC CYANAMIDE II. CND0/2
J. B. MOFFAT Department
STRUCTURE
AND NONPLANARITY
OF
CALCULATIONS
AND
K. F. TANG
of Chemistry,
Unicersity
of Waterloo,
Waterloo,
Ontario
(Canada)
(Received April 27th, 1971)
ABSTRACT
calculations on various nuclear configurations provide evidence for the nonplanar geometry of cyanamide. The out-of-plane angle is calculated to be 56” and a barrier to inversion of 0.0120 hartree is found. CNDO/:!
INTRODUCTION
The results of some ab initio calculations1 on cyanamide using a basis set of 26 Gaussian functions indicate that the nonplanar is more stable than the planar configuration. A review’ of the experimental work on cyanamide showed that data
exist supporting
both configurations.
Recently Jones and Sheppard2 estimated
the out-of-plane angle to be 43” f 1.5’ and the inversion barrier as 467+30 cm-’
from their vapour phase spectroscopic study of cyanamide. It seemed interesting and valuable to employ one of the many available semi-empirical methods of calculation to examine a variety of nuclear configurations of cyanamide in an attempt to find further theoretical support for the nonplanar geometry.
METHOD
were performed for various out-of-plane angles. using the internuclear separations (Table 1) of Millen, Topping and Lide3 and also those of Macdonald, Taylor, Tyler and Sheridan4. The Pople and Segal’ CNDO/~programme was modified for our purposes. The out-of-plane angle is defitied here as the angle between the bisector of the HN,H angle and the C-N- bond extetided. CNDO/~
calculations
J. Mol. Structure, 10 (1971) 285-289
J. B. MOFFAT,
286 TABLE
K. F. TANG
1
INTERNUCLEAR
SEPARATIONS
FOR CYANAMIDE
(Bohr)
Configuration
A
B
WY=
(Ref. 4)
3)
N1-Nz= N,C N,-H
4.7357 2.5096 1.7744
4.7357 2.5436 1.8917
LHN~H
120”
113”31’
a Amino nitrogen is N1 ; cyanide nitrogen is N+.
RESULTS
AND
DISCUSSION
The total energies calculated with both sets of internuclear separations and for various out-of-plane angles are shown in Fig. 1. The corresponding barriers to inversion (Fig. 1) are approximately two and six times the value of 0.0021 hat-tree estimated by Jones and Sheppard. The out-of-plane angles corresponding to configurations having the lowest total energies are approximately 46” and 56” for the internuclear distances of TABLE 2 RESULTS
OF THE CALCULATIONS
ENERGIES
ON THE NUCLEAR
CONFIGURATIONS
FOR CYANAMIDE=
Configfiration Out-of-plane
A angle
B 56O
46O
Orbital energies
-
1st unoccupied
1.5998 1.3838 0.9341 0.8738 0.7880 0.6358 0.5732 0.5070 0.2379
-
1.5711 1.3898 0.9052 0.8673 0.7867 0.6359 0.5797 0.5228 0.2331
Electronic energy
-63.8199
-63.5013
Total energy
-31.5829
-31.6346
Ionization energy
0.5070
0.5228
Dipole.moment
3.825
3.074
p Eneigies J: Mol.
(D)
are in hartrees.
Stiuctwe,
10.(1971) 28S289
YIELDING
THE LOWEST
TOTAL
ELECTRONIC
STRUCTURE
AND
NONPLANARITY
OF CYANAMIDE.
II.
287
-31.575
c -31.580
-
-31.5n2r : f -31.620
-
TOTAL ENERGY WbClmSe) c-
-31.62s
T 0.01196
-31.430
-
_j\_I -31.635
0
20 OUT-OF-PLANE
80
40 ANGLE
Fig. 1. Total energy of cyanamide as a function of out-of-plane angle.
Millen and of Macdonald, respectively. It is of interest to note that the latter configuration produces a total energy at 56” which is lower than that of the former configuration at 46”. However, the internuclear distances of Millen and an out-ofplane angle of 46” agrees more closely with the Jones and Sheppard estimate of 43” f 1.5” for the out-of-plane angle. Table 2 lists the results of the calculations on the nuclear configurations of
cyanamide given in Table 1 which, with the out-of-plane angles previously mentioned gave the lowest total energies. No experimental value for the ionization energy is available for cyanamide, however, Tyler6 found a value of 4.3 D for the dipole moment. It may be seen that the calculated value for the dipole moment given in Table 2 differs considerably from the experimental value. J. Mol. Sirucr~e, 10 (1971) 285-1289
288
J.
B. MOFFAT,
K. F. TANG
The total atomic electron densities are given in Table 3 for both cotigurations A and B. Table 4 records numerical values of the data given in Fig. 1. While the present results do not, of course, prove that the cyanamide.molecule has a nonpIanar structure, they are in quite reasonable agreement with the most recent experimental data. Further, the present work appears to lend further support to the usefulness of the semi-empirical CNDO method in calculations of chemical interest. TABLE 3 TOTAL
ELECTRON
DENSITIES
Configuration Atom Out-of-plane
ON ATOMS
A
B
Nl
C
H
0”
5.222
3.826
5.230
0.860
8”
5.219
3.830
5.230
0.860
NZ
H
c
NZ
5.219
3.816
5.222
0.871
5.217
3.818
5.221.
0.871
Nl
0ngIe
16O
5.226
3.823
5.225
0.862
5.212
3.823
5.219
0.873
24O
5.224
3.826
5.222
0.863
5.206
3.829
5.214
0.875
32”
5.209
3.839
5.222
0.864
5.221
3.819
5.203
0.878
5.212
3.828
5.198
0.880
40”
5.220
3.831
5.215
0.866
46”
*5.220
3.832
5.212
0.867
48O
5.230
3.825
5.209
0.868
56O
5.236
3.820
5.206
0.868
64”
5.222
3.834
5.211
0.866
72’
5.240
3.820
5.210
0.865
5.197
3.843
5.197
0.882
3.836
5.190
0.883
5.214
3.832
5.187
0.883
5.202
3.845
5.192
0.880
*X207
Lowest total energies.
l
TABLE TOTAL
4 ENERGY
Out-of-plane (degrees)
OF CYANAMIDE
angle
FOR VARIOUS
OUT-OF-PLANE
Configuration A
B
0
-31.57899
-31.62267
8
-31.57896
-31.62279
16
-31.57965
-31.62462
24
-31.58058
-31.62697
32
-31.58231
-31.62968
40
-31.58295
-31.63211
48
-31.58334
-31.63411
.56
-31.58241
-31.63463
64
-31.57957
-31.63399
72
-31:57594
-31.63138
J. .MoI. Structtiri.
-10mC1971> 2851289
ANGLES
ELECTRONIC
STRUCTURE
AND
NONPLANARITY
OF
CYANAMIDE.
II.
289
ACKNOWLEDGEMJZNTS
Financial support of the National Research Council of Canada in the form of an operating grant (LB-M.) and a bursary (K.F.T.) is gratefully acknowledged. The cooperation and assistance of the University of Waterloo Computer Centre is much appreciated. The kindness of the Quantum Chemistry Program Exchange for provision of a copy of the Pople-Segal programme is appr&iated.
REFERENCES 1 J. B. MOFFAT AND C. VOGT, J. Mol. Spectrosc., 33 (1970) 494. 2 T. R. JONESAND N. SHEPPARD, Chem. Cornmun.. (197Oj il5. 3 D. J. MILLEN- G. TOPPING AND D. R. LIDE, JR., J. Mol. Spectrosc.. 8 (1962) 153. 4 f. N. MACDONALD, D. TAYLOR,J. K.TYLER AND J. SHERIDAN,J. hf~l~Specrm.w.,26 (1968) 285.. 5 J. A. POPLE AND G. A. SEGAL. i. Chem. Phys., 43 (1965) SI 36_ 6 J. K. TYLER, L. F. THOMAS AND J. SHERIDAN, Pmt. Chem. Sm., London, (1959) 155. J. Mol. Strrrcture, 10 (1971)
285-289
Structure
285
Elsevier Publishing Company, Amsterdam. Printed in the Netherlands
THE ELECTRONIC CYANAMIDE II. CND0/2
J. B. MOFFAT Department
STRUCTURE
AND NONPLANARITY
OF
CALCULATIONS
AND
K. F. TANG
of Chemistry,
Unicersity
of Waterloo,
Waterloo,
Ontario
(Canada)
(Received April 27th, 1971)
ABSTRACT
calculations on various nuclear configurations provide evidence for the nonplanar geometry of cyanamide. The out-of-plane angle is calculated to be 56” and a barrier to inversion of 0.0120 hartree is found. CNDO/:!
INTRODUCTION
The results of some ab initio calculations1 on cyanamide using a basis set of 26 Gaussian functions indicate that the nonplanar is more stable than the planar configuration. A review’ of the experimental work on cyanamide showed that data
exist supporting
both configurations.
Recently Jones and Sheppard2 estimated
the out-of-plane angle to be 43” f 1.5’ and the inversion barrier as 467+30 cm-’
from their vapour phase spectroscopic study of cyanamide. It seemed interesting and valuable to employ one of the many available semi-empirical methods of calculation to examine a variety of nuclear configurations of cyanamide in an attempt to find further theoretical support for the nonplanar geometry.
METHOD
were performed for various out-of-plane angles. using the internuclear separations (Table 1) of Millen, Topping and Lide3 and also those of Macdonald, Taylor, Tyler and Sheridan4. The Pople and Segal’ CNDO/~programme was modified for our purposes. The out-of-plane angle is defitied here as the angle between the bisector of the HN,H angle and the C-N- bond extetided. CNDO/~
calculations
J. Mol. Structure, 10 (1971) 285-289
J. B. MOFFAT,
286 TABLE
K. F. TANG
1
INTERNUCLEAR
SEPARATIONS
FOR CYANAMIDE
(Bohr)
Configuration
A
B
WY=
(Ref. 4)
3)
N1-Nz= N,C N,-H
4.7357 2.5096 1.7744
4.7357 2.5436 1.8917
LHN~H
120”
113”31’
a Amino nitrogen is N1 ; cyanide nitrogen is N+.
RESULTS
AND
DISCUSSION
The total energies calculated with both sets of internuclear separations and for various out-of-plane angles are shown in Fig. 1. The corresponding barriers to inversion (Fig. 1) are approximately two and six times the value of 0.0021 hat-tree estimated by Jones and Sheppard. The out-of-plane angles corresponding to configurations having the lowest total energies are approximately 46” and 56” for the internuclear distances of TABLE 2 RESULTS
OF THE CALCULATIONS
ENERGIES
ON THE NUCLEAR
CONFIGURATIONS
FOR CYANAMIDE=
Configfiration Out-of-plane
A angle
B 56O
46O
Orbital energies
-
1st unoccupied
1.5998 1.3838 0.9341 0.8738 0.7880 0.6358 0.5732 0.5070 0.2379
-
1.5711 1.3898 0.9052 0.8673 0.7867 0.6359 0.5797 0.5228 0.2331
Electronic energy
-63.8199
-63.5013
Total energy
-31.5829
-31.6346
Ionization energy
0.5070
0.5228
Dipole.moment
3.825
3.074
p Eneigies J: Mol.
(D)
are in hartrees.
Stiuctwe,
10.(1971) 28S289
YIELDING
THE LOWEST
TOTAL
ELECTRONIC
STRUCTURE
AND
NONPLANARITY
OF CYANAMIDE.
II.
287
-31.575
c -31.580
-
-31.5n2r : f -31.620
-
TOTAL ENERGY WbClmSe) c-
-31.62s
T 0.01196
-31.430
-
_j\_I -31.635
0
20 OUT-OF-PLANE
80
40 ANGLE
Fig. 1. Total energy of cyanamide as a function of out-of-plane angle.
Millen and of Macdonald, respectively. It is of interest to note that the latter configuration produces a total energy at 56” which is lower than that of the former configuration at 46”. However, the internuclear distances of Millen and an out-ofplane angle of 46” agrees more closely with the Jones and Sheppard estimate of 43” f 1.5” for the out-of-plane angle. Table 2 lists the results of the calculations on the nuclear configurations of
cyanamide given in Table 1 which, with the out-of-plane angles previously mentioned gave the lowest total energies. No experimental value for the ionization energy is available for cyanamide, however, Tyler6 found a value of 4.3 D for the dipole moment. It may be seen that the calculated value for the dipole moment given in Table 2 differs considerably from the experimental value. J. Mol. Sirucr~e, 10 (1971) 285-1289
288
J.
B. MOFFAT,
K. F. TANG
The total atomic electron densities are given in Table 3 for both cotigurations A and B. Table 4 records numerical values of the data given in Fig. 1. While the present results do not, of course, prove that the cyanamide.molecule has a nonpIanar structure, they are in quite reasonable agreement with the most recent experimental data. Further, the present work appears to lend further support to the usefulness of the semi-empirical CNDO method in calculations of chemical interest. TABLE 3 TOTAL
ELECTRON
DENSITIES
Configuration Atom Out-of-plane
ON ATOMS
A
B
Nl
C
H
0”
5.222
3.826
5.230
0.860
8”
5.219
3.830
5.230
0.860
NZ
H
c
NZ
5.219
3.816
5.222
0.871
5.217
3.818
5.221.
0.871
Nl
0ngIe
16O
5.226
3.823
5.225
0.862
5.212
3.823
5.219
0.873
24O
5.224
3.826
5.222
0.863
5.206
3.829
5.214
0.875
32”
5.209
3.839
5.222
0.864
5.221
3.819
5.203
0.878
5.212
3.828
5.198
0.880
40”
5.220
3.831
5.215
0.866
46”
*5.220
3.832
5.212
0.867
48O
5.230
3.825
5.209
0.868
56O
5.236
3.820
5.206
0.868
64”
5.222
3.834
5.211
0.866
72’
5.240
3.820
5.210
0.865
5.197
3.843
5.197
0.882
3.836
5.190
0.883
5.214
3.832
5.187
0.883
5.202
3.845
5.192
0.880
*X207
Lowest total energies.
l
TABLE TOTAL
4 ENERGY
Out-of-plane (degrees)
OF CYANAMIDE
angle
FOR VARIOUS
OUT-OF-PLANE
Configuration A
B
0
-31.57899
-31.62267
8
-31.57896
-31.62279
16
-31.57965
-31.62462
24
-31.58058
-31.62697
32
-31.58231
-31.62968
40
-31.58295
-31.63211
48
-31.58334
-31.63411
.56
-31.58241
-31.63463
64
-31.57957
-31.63399
72
-31:57594
-31.63138
J. .MoI. Structtiri.
-10mC1971> 2851289
ANGLES
ELECTRONIC
STRUCTURE
AND
NONPLANARITY
OF
CYANAMIDE.
II.
289
ACKNOWLEDGEMJZNTS
Financial support of the National Research Council of Canada in the form of an operating grant (LB-M.) and a bursary (K.F.T.) is gratefully acknowledged. The cooperation and assistance of the University of Waterloo Computer Centre is much appreciated. The kindness of the Quantum Chemistry Program Exchange for provision of a copy of the Pople-Segal programme is appr&iated.
REFERENCES 1 J. B. MOFFAT AND C. VOGT, J. Mol. Spectrosc., 33 (1970) 494. 2 T. R. JONESAND N. SHEPPARD, Chem. Cornmun.. (197Oj il5. 3 D. J. MILLEN- G. TOPPING AND D. R. LIDE, JR., J. Mol. Spectrosc.. 8 (1962) 153. 4 f. N. MACDONALD, D. TAYLOR,J. K.TYLER AND J. SHERIDAN,J. hf~l~Specrm.w.,26 (1968) 285.. 5 J. A. POPLE AND G. A. SEGAL. i. Chem. Phys., 43 (1965) SI 36_ 6 J. K. TYLER, L. F. THOMAS AND J. SHERIDAN, Pmt. Chem. Sm., London, (1959) 155. J. Mol. Strrrcture, 10 (1971)
285-289