Telluroaldehyde Similarities and differenes with ：telluroaldehyde的相似性和差異性

1、telluroformaldehyde: similarities and differences with chalcogens of formaldehyde presented bymiss jaufeerally b. naziah for the 2009-2010 doctorial consortium1my introduction i did my bsc(hons) chemistry at university of mauritius (2006-2009). currently i am enrolled for mphil/phd in the field of c

2、omputational 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: .2abstract a systematic investigation of the molecular parameters (bond lengths, bond angles, dipole moments, rotational

3、 constants), the vibrational ir spectra and the homo-lumo gap of telluroformaldehye are carried out at mp2, b3lyp, blyp and bhlyp level with double- basis sets with polarization and diffuse functions, denoted as dzp+.the lanl2dzdp ecp is used for tellurium. the results obtained are compared with the

4、 reported experimental and theoretical data available for formaldehyde, thioformaldehyde and selenoformaldehyde.3 introduction computational methods results and discussion summary future work acknowledgementscontent of this presentation4introductioninterest in the knowledge of the physicochemical an

5、d 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 p-p bonding would not be stable until methanal and its analogues namely,

6、 thiomethanal and selenomethanal 1-2 were isolated. since then, literature has been flooded with studies consisting of these chalcogens 3,4. 1) kwiatkowski j. s.; leszczy ski j. mol. phys., 81, 119, 1994. 2) beukes j. a.; danna b.; bakken v.; nielsen c. j. pccp, 2, 4049, 2000.3) r. west, m. j. fink;

7、 j. michl, science 214, 1343, 1981. 4) yoshifuji m.; shima i.; inamoto n.; hirotsu k.; higuchi t. j. am. chem. soc. 103, 4587, 1981.5 formaldehyde and its derivatives are the key components in the chemistry of atmosphere 5, they are also primary pollutants produced by partial oxidation of hydrocarbo

8、n 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

9、halogenosubstitution of formaldehyde play an important role in biochemistry 7. importance of formaldehyde and its analogues5) 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, 1975.6

10、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 react

11、ions 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, 199

12、9.11) iwamoto t.; sato k.; ishida s.; kabuto c.; kira m., j. am. chem. soc., 128, 16914, 2006.importance of formaldehyde and its analogues7increasing interest in tellurium compoundsnowadays tellurium compounds are in great interest both in experimental and theoretical studies due to: heavy ketones o

13、f tellurium undergo cycloaddition reactions forming novel compounds 9-11. antioxidant properties of synthetic organotellurium compounds 8. the availability of 125te nmr spectroscopy 8. 8 the increasing interest in the knowledge of the physicochemical and spectroscopic properties of the cx2y molecula

14、r 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.9increasing interest in t

15、ellurium compounds continuedcomputational 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 fun

16、ctionals used are: mp2, b3lyp, blyp and bhlyp. the double- 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

17、) 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

18、b. j.; gilbert t. m.; sunderlin l. s.; j. phys. chem. a, 105, 8111, 2001.10 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 vibratio

19、nal 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.computational methods continued11results and discussion to our knowledge there is no experimental data available for telluroformaldehy

20、de 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 molec

21、ules 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, 2006.12molecular parameters of the chalcogens a kwiatkowski j. s.; leszczyski, j. mol. phys., 81, 119, 1994. b chin-hun

22、g. l.; ming-der s., san-yan.c., j. phys. chem., 105, 6932, 2001. c kwiatkowski j. s.; leszczyski , j. mol. phys., 97, 1845, 1993.13 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

23、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 exp

24、erimental values.results and discussion continued14 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 al

25、l 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.ir vibrational data of formaldehyde and its analogues15table 1. calculated and experimental spectra of ch2x (x=o, s, se, te) references a, b an

26、d c are same as in slide 13.16 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

27、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.17results and discussion continuedmp2expe

28、rimenth2co2.169a2.33aa2868081.25a281970.00ab38543.37a38836.05ac33967.03a34002.20ah2cs1.492c1.65ca292786.76c291710.00cb17678.23c17698.87cc16671.62c16652.98ch2cse1.354a1.41aa291113.25a294803.00ab12405.47a12404.01ac11898.43a11878.40ah2cte0.345-a289561.54-b9517.68-c9214.80-table 2. dipole moments and ro

29、tational constants of the chalcogensdipole moments, , in d and rotational constants, a, b, c in mhz.18 references a and c are same as in slide 13. the theoretical and experimental values for the dipole moments are in good agreement. the electron correlation contributions improve the accuracy of the

30、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 grou

31、p. moreover there is a good agreement between the calculated and the experimental values for the rotational constants.19results and discussion continuedionization energy of formaldehyde and its analoguesh2coh2csh2cseh2ctei.e at mp2 level1033.37 17876.10 20827.85 20702.07experimental i.e1049.78 18,19

32、910.84 19849.09 20-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, 19

33、92. 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, 6589,1993.20 the experimental and theoretical data for c=o and c=se are

34、 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. 21homo-lumo gap literature 21 reports that there is a significant lowering of the en

35、ergy of the * 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 ch2och2sch2sech2te * * * *nnn55.09 kj/m

36、ol22.09 kj/mol13.80 kj/mol 9.09 kj/mol21) orlova.g., goddard.j.d., j. org. chem.,66, 4026, 2001.22summarymoving 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.