Transcript Telluroformaldehyde: Similarities and differences with

Telluroformaldehyde: Similarities
and Differences with Chalcogens of
Formaldehyde
Presented by
Miss Jaufeerally B. Naziah
for the 2009-2010 Doctorial
Consortium
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My introduction
• I did my BSc(Hons) Chemistry at University of Mauritius
(2006-2009).
• Currently I am enrolled for MPhil/PhD in the field of
Computational Chemistry, under the supervision of Assoc.
Prof P. Ramasami and Prof. H. F. Schaefer III at the
University of Mauritius.
• I can be contacted through the email-address:
[email protected].
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Abstract
A systematic investigation of the molecular parameters
(bond lengths, bond angles, dipole moments, rotational
constants), the vibrational IR spectra and the HOMOLUMO gap of telluroformaldehye are carried out at MP2,
B3LYP, BLYP and BHLYP level with double-ζ basis sets
with polarization and diffuse functions, denoted as
DZP++.The LANL2DZdp ECP is used for tellurium. The
results obtained are compared with the reported
experimental and theoretical data available for
formaldehyde, thioformaldehyde and selenoformaldehyde.
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Content of this presentation
•
•
•
•
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Introduction
Computational methods
Results and discussion
Summary
Future Work
Acknowledgements
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Introduction
• Interest in the knowledge of the physicochemical and
spectroscopic properties of CX2Y molecular series (X=H, F, Cl,
Br; Y=O, S, Se) has grown in the last two decades.
• In the past, it was considered that heavy ketones ( Group 14
element-Group 16 element bonded compounds), having pπ-pπ
bonding would not be stable until methanal and its analogues
namely, thiomethanal and selenomethanal [1-2] were isolated.
•
Since then, literature has been flooded with studies consisting of
these chalcogens [3,4].
1)
2)
3)
4)
Kwiatkowski J. S.; Leszczy ski J. Mol. Phys., 81, 119, 1994.
Beukes J. A.; D'anna B.; Bakken V.; Nielsen C. J. PCCP, 2, 4049, 2000.
R. West, M. J. Fink; J. Michl, Science 214, 1343, 1981.
Yoshifuji M.; Shima I.; Inamoto N.; Hirotsu k.; Higuchi T. J. Am. Chem. Soc. 103, 4587, 1981.
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Importance of formaldehyde and its analogues
• Formaldehyde and its derivatives are the key components in the
chemistry of atmosphere [5], they are also primary pollutants
produced by partial oxidation of hydrocarbon fuels and
secondary pollutants, produced by the oxidation of volatile
organic compounds.
• Thio and selenoketones are useful in the preparation of
intriguing molecules such as extremely sterically hindered
olefins [6].
• The effect on the substitution of oxygen to sulphur, selenium or
tellurium and the halogenosubstitution of formaldehyde play an
important role in biochemistry [7].
5) Kotzias D.; Konidara C. SPB Academic Publishers, 67, 1997.
6) Guziec F. S.; Sanfilippo L. J. Tetrahedron, 44, 6241, 1988.
7) Damani L. Adv. Heterocyclic Chem., 18, 199, 1975.
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Importance of formaldehyde and its analogues
• Thio analogues are among the most active and some of
them are known to exhibit activity against certain types of
tumours [2].
• Telluro analogues are of significant interest due to the
antioxidant properties of synthetic organotellurium
compounds [8].
• Heavy ketones of tellurium undergo cycloaddition reactions
forming novel compounds [9-11].
8) Mugesh G.; Panda A.; Apte S.; Singh H., The Fifth International Electronic Conference on Synthetic Organic Chemistry, 2001.
9) Tokitoh N., Phosphorus Sulphur and Silicon, 136, 123-138, 1998.
10) Matsumoto T.; Tokitoh N.; Okazaki R., J. Am. Chem. Soc. 121, 8811, 1999.
11) Iwamoto T.; Sato K.; Ishida S.; Kabuto C.; Kira M., J. Am. Chem. Soc., 128, 16914, 2006.
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Increasing interest in tellurium compounds
Nowadays tellurium compounds are in great interest both in
experimental and theoretical studies due to:
 heavy ketones of tellurium undergo cycloaddition reactions
forming novel compounds [9-11].
 antioxidant properties of synthetic organotellurium compounds
[8].
 the availability of 125Te NMR spectroscopy [8].
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Increasing interest in tellurium compounds [continued]
 the increasing interest in the knowledge of the
physicochemical and spectroscopic properties of the CX2Y
molecular series [2].
 the explosive growth of computational power.
 the availability of user friendly software which help
theoretical studies to predict the molecular parameters and
spectroscopic data for novel, yet unsynthesised molecules.
 the availability of basis sets for tellurium.
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Computational methods
• Geometrical parameters, adiabatic electron affinities,
ZPVE-corrected electron affinities, vertical electron
affinities and vertical detachment energies of the anions,
and singlet-triplet gaps will be computed with the Gaussian
03 program [12].
• The functionals used are: MP2, B3LYP, BLYP and BHLYP.
• The double-ζ basis sets with polarization and diffuse
functions, denoted as DZP++ [13] are used and
LANL2DZdp ECP [14] for tellurium.
12) M. J. Frisch; G. W. Trucks; H. B. Schlegel, et al., Gaussian 03, Revision A.1, Gaussian, Inc., Pittsburgh PA, USA, 2003.
13) Huzinaga S. J. Chem. Phys. 1965, 42, 1293. Dunning T. H.; Hay P. J. In Modern Theoretical Chemistry, Schaefer, H. F., Ed. Plenum
New York, 1977, 3, 1. Huzinaga S. Approximate Atomic Wavefunctions II, University of Alberta: Edmonton, Alberta, 1971.
14) Check C. E.; Faust T. O.; Bailey J. M.; Wright B. J.; Gilbert T. M.; Sunderlin L. S.; J. Phys. Chem. A, 105, 8111, 2001.
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Computational methods [continued]
• Natural bond theory to understand bonding in the
molecules.
• The optimized structures will be verified to be true
minima by performing frequency computations.
• GAUSS-VIEW program for visual inspection and animation
of vibrational modes [15].
15) Gaussview, Version 3.09, R. Dennington II, Keith T.; Millam J.; Eppinnett K.; Hovell W. L.; Gilliland R.; Semichem, INC.,
Shawnee Mission, KS, 2003.
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Results and discussion
• To our knowledge there is no experimental data available
for telluroformaldehyde [16].The optimized geometries
(bond lengths and bond angles) of telluromethanal were
calculated by all the four functionals stated.
• The model systems containing the >C=O, >C=S, >C=Se,
>C=Te are considered to study the trends in the changes of
molecular geometries and vibrational IR spectra of the
molecules on the substitution with progressively heavier
atoms down the group 16 of the periodic table.
16) Jansson.. E, Norman,.P,. Minaeve .B., Agren . H., J. Phys. Chem., 124, 114016, 2006.
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Molecular parameters of the chalcogens
a Kwiatkowski J. S.; Leszczyski, J. Mol. Phys., 81, 119, 1994.
b Chin-Hung. L.; Ming-Der S., San-Yan.C., J. Phys. Chem., 105, 6932, 2001.
c Kwiatkowski J. S.; Leszczyski , J. Mol. Phys., 97, 1845, 1993.
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Results and discussion [continued]
• The results show that the stability of the C=X (X=O, S, Se,
Te) double bond decreases as there is a gradual increase in
bond length. This suggests that moving down the Group 16,
the atomic overlap becomes poorer.
• From >C=O to >C=Se, slight increase in the HCH bond
angle is observed, whereas that of C=Se and C=Te is
approximately the same.
• However, there is no apparent change in the C-H bond
length of these chalcogens.
• MP2 results are in better agreement with the experimental
values.
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IR vibrational data of formaldehyde and its
analogues
• Since it is believed that MP2 calculations furnish more
reliable data, available experimental vibrational IR spectra of
the chalcogens are compared only at the MP2 level.
• The calculated harmonic IR spectra (wavenumbers, absolute
intensities) for all the species in question are compared with
the available experimental data in Table 1.
• The available MP2 wavenumbers are scaled by a single
factor of 0.967.
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Table 1. Calculated and experimental spectra of CH2X (X=O, S, Se, Te)
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References a, b and c are same as in slide 13.
Results and discussion [continued]
• There is a good agreement between the theoretical and
experimental results. Except in the case of the parent
compound formaldehyde, the agreement between the scaled
MP2 wavenumbers and the experimental fundamental
wavenumbers do not agree perfectly.
• The wavenumbers of the symmetric and asymmetric CH
stretching modes are higher and this is because the
anharmonicities for these modes are much greater than
those of the remaining modes [2].
• The IR intensity of CH asym stretching is the highest, but it
decreases from >C=O to >C=Te.
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Table 2. Dipole moments and Rotational constants of the Chalcogens
MP2
Experiment
H2CO
µ
2.169a
2.33a
A
2868081.25a
281970.00a
B
38543.37a
38836.05a
C
33967.03a
H2CS
34002.20a
µ
1.492c
1.65c
A
292786.76c
291710.00c
B
17678.23c
17698.87c
C
16671.62c
H2CSe
16652.98c
µ
1.354a
1.41a
A
291113.25a
294803.00a
B
12405.47a
12404.01a
C
11898.43a
H2CTe
11878.40a
µ
A
0.345
289561.54
-
B
9517.68
-
C
9214.80
-
Dipole moments, µ, in D and rotational constants, A, B, C in MHz.
References
a and c
are same as in slide 13.
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Results and discussion [continued]
• The theoretical and experimental values for the dipole moments
are in good agreement. The electron correlation contributions
improve the accuracy of the dipole moments [2].
• There is a gradual decrease in dipole moment while moving from
>C=O to >C=Te which suggests that the separation of charges is
lowered and the equal sharing of the bonding electrons is narrowed
down the group.
• Therefore it adds to the fact that the C=X bond gets weakened
down the group.
• Moreover there is a good agreement between the calculated and
the experimental values for the rotational constants.
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Ionization energy of formaldehyde and its analogues
To study the trend in the 1st ionization energy (I.E) of the
formladehyde-chalcogens, the available experimental and
theoretical data are summarized in table 3.
Table 3. 1st I.E of the formaldehyde-chalcogens in kJ/mol
I.E at MP2 level
Experimental I.E
H2CO
1033.37 [ 17]
1049.78 [18,19]
H2CS
876.10 [20]
910.84 [19]
H2CSe
827.85 [ 20]
702.07
849.09 [ 20]
-
H2CTe
17) Rossi. A. R., Davidson.E.R., J . Phys. Chem., 96, 10682, 1992.
18) Ohno.K., Okamura.K., Yamakado.H., Hoshino.S.,Takami.T., Yamauchi.M., J. Phys. Chem.,99, 14247, 1995.
19) Jones.A., Lossing.F.P., J. Phys. Chem., 71, 4111, 1967.
20) Collins.S., Back.T.G., Rauk.A., J. Am. Chem. Soc., 107, 6589,1993.
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Graph 1. Ionization energy of the FormaldehydeChalcogens in kJ/mol
1100
1050
CH2O
1000
1st I.E in kJ/mol
950
900
850
800
CH2S
calculated values
experimental values
CH2Se
750
700
CH2Te
650
600
Formaldehyde-Chalcogens
• The experimental and theoretical data for >C=O and >C=Se are quite
close.
• There is a gradual decrease in the 1st I.E down the group. This is
expected, as the size of the Group 16 element increases and thus the
distance between the valence electrons and the nucleus increases.
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HOMO-LUMO gap
• Literature [21] reports that there is a significant lowering of
the energy of the π* LUMO on changing C to S and a
moderate lowering on changing S to Te. The HOMO of the
chalcogens is an n-orbital that corresponds to a lone pair on
the chalcogen atom, except for Formaldehyde.
Sketch 1 . HOMO-LUMO gap of the Formaldehyde-Chalcogens
CH2O
CH2S
CH2Se
CH2Te
π*
π*
55.09
kJ/mol
22.09
kJ/mol
n
π*
13.80
kJ/mol
n
π*
9.09 kJ/mol
n
π
21) Orlova.G., Goddard.J.D., J. Org. Chem.,66, 4026, 2001.
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Summary
Moving down the Group16 for the model series of CH2X (X=O,
S, Se, Te) the:
• C=X bond length increases and the bond strength decreases.
• HCH bond angle increases slightly.
• dipole moment decreases gradually.
• rotational constants remain almost the same.
• IR intensity of CH asym stretching decreases.
•1st I.E decreases gradually.
• HOMO-LUMO gap decreases significantly.
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Future Work
• Since there is a remarkable progress in the chemistry of
ketones of heavier elements, especially in the field of Group
14 elements [22-24], the carbon of methanal can be replaced
by silicon and germanium. Besides, the influence of monoand dihalogeno substitution (F, Cl, Br, CN) on the molecular
parameters can also be explored due to their interesting
bonding character and to predict the trends in the changes of
molecular geometries and spectral data.
• Studying the aqua-complexes of all these congeners of
formaldehyde.
•
Publishing the results obtained.
22) R. West, M. J. Fink; J. Michl, Science 214, 1343, 1981.
23) Yoshifuji M.; Shima I.; Inamoto N.; Hirotsu k.; Higuchi T. J. Am. Chem. Soc. 103, 4587, 1981.
24) Brook A.; Abdesaken F.; Gutekunst G.; Kallury R.; J. Am. Chem. Soc. Commun., 191, 1981.
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Acknowledgements
I gratefully acknowledge:
 the organising committee of the Doctorial Consortium.
 the support of my supervisor Assoc. Prof. P Ramasami and
Dr H Abdallah.
 the Tertiary Education Commision (TEC) for the grant of
MPhil/PhD Scholarship.
 the facilities from the University of Mauritius.
 the School of Chemical Sciences, Universiti Sains
Malaysia.
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