1 / 25

My introduction

Telluroformaldehyde : Similarities and Differences with Chalcogens of Formaldehyde Presented by Miss Jaufeerally B. Naziah for the 2009-2010 Doctorial Consortium. My introduction . I did my BSc(Hons) Chemistry at University of Mauritius (2006-2009).

hanne
Download Presentation

My introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Telluroformaldehyde: Similarities and Differences with Chalcogens of Formaldehyde Presented byMiss Jaufeerally B. Naziah for the 2009-2010 Doctorial Consortium

  2. 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: naziah0512@gmail.com.

  3. Abstract A systematic investigation of the molecular parameters (bond lengths, bond angles, dipole moments, rotational constants), the vibrational IR spectra and the HOMO-LUMO 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.

  4. Content of this presentation • Introduction • Computational methods • Results and discussion • Summary • Future Work • Acknowledgements

  5. 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]. 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.

  6. 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.

  7. 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.

  8. 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].

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Molecular parameters of the chalcogens a Kwiatkowski J. S.; Leszczyski, J. Mol. Phys., 81, 119, 1994. bChin-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.

  14. 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.

  15. 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.

  16. Table 1. Calculated and experimental spectra of CH2X (X=O, S, Se, Te) References a, b and c are same as in slide 13.

  17. 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.

  18. Table 2. Dipole moments and Rotational constants of the Chalcogens Dipole moments, µ, in D and rotational constants, A, B, C in MHz. References aand c are same as in slide 13.

  19. 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.

  20. 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 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.

  21. 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.

  22. 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 * π * π * 22.09 kJ/mol 13.80 kJ/mol 55.09 kJ/mol 9.09 kJ/mol n n n π 21) Orlova.G., Goddard.J.D., J. Org. Chem.,66, 4026, 2001.

  23. 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. Summary

  24. 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 mono- and 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.

  25. 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.

More Related