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Selenirene as an intermediate in the pyrolysis of 1,2,3-selenadiazole. Microwave spectra of 13C labelled selenoketene
1 March 1981
CHEMICAL PHYSICS UXTERS
Volume 78, number 2
SELENIRENE AS AN ~TE~ED~TE IN THE PYROLYSIS OF 1,2,3SELENADIAZOLE. MZCROWAVE §PECTRA OF 13C LABELLED SELENOKETENE B@rge BAK, Niels A. KRISTIANSEN, Hen& SVANHOLT Chemical Laboratory V. The H.C. orsted Institute, University of Copenhagen, DK-X00 Copenhagen @, Denmark
and Arne HOLM and Steen ROSENKILDE Chemical Laboratory II, The KC. &wed DK-ZOO Copenhagen @, Denmark
Instr’tute, Unwersity
of Copenhagen,
Received24 November 1980 Microwavespectraof ‘3CH~=1iC=s0~78Se and ‘2CH~=*3C=80~78Se fselenoketene)are recorded. By pyrolysis of .5-13C-l ,2,3-selenadiazoleall four speciesare formed. The 13C scramblingmay take place via a threemembered ring, selenirene,but as expected its microwavespectrumwas not observed.
1. Experimental In a “flow” system 1 JJ-selenadiazob (1) pyrolyzes to selenoketene (II) on a hot (SOO-700°C) quartz surface at 10-100 mTorr, conveniently monrtored by microwave (MW) detection 111. By pyrolysis of isotopic species of f structural information on II has been obtained [1,23. MW spectra of 13CH2=12C,80~78Se (III) and %H2= 13C=80~78Se (IV) have now been recorded from 90% ~3C-enriched samples of 4-13C-I (w 5 mg) and 5-U C-I (R 10 mg). Hereby an earlier minor ambiguity in the published selenoketene “substitution” structure has been removed 121. However, the main
““I
N
‘35 \-iii
I 532-I
Fig.
1.
purpose of this paper is to provide exp~~rn~nta~ MW transrrzon frequencies and intensities of HI and IV for examination of possrble carbon-atom scmmbling when vapor of I passes the hot zone converting, for example, as sketched in fig. 1. 4-13C-I and 5-u C-i were prepared f3] from 90% UC-enriched 12CH3UCH20H and I3 C& ‘2CH,0H, respectively. The recorded MW spectra of III and IV are given in tables 1 and 2, +JBe appropriate rotational and distortion constants are reported in table 3, The final “substitution” structure of II now based on enriched species throughout is presented in table 4, not calling for further comments than already given in ref. f2] .
As-
Ez
8os’e
s&
1
1 5L
Possibiereaction path for 5-‘3C-1,2,3-se~enadiazohto CHa =13C=Se
selenireue0
H”
.
m
(IHI throughan intermediate
duringpyroiysis.
0 OOQ-2614/81/0000-0000/$02.50
0 North-Holland
Publishing Company
301
Volume
CHEhIICAL
78, number 2
PHYSICS
Table 1 Ground-state,
Joerotational transitions in MHz ofgaseous 13CH2 =12C=80Se and 13CH2 =l*C= 78Se produced by lowpressure pyrolysis of 4-i3C-1 .2,3-selenadiazole at 900 K. Mrcrowaye ceil at room temperature and a total pressure of 15 mTorr (flow system) c____._.._._ _-...-. .-. --. --
ohs. ._--_____--_
--_
*3CH2=‘2C=78Se
r3C& =‘2C,80Se
Transtion
obs. - talc _.-.
322 - 423 32r422
29436 83 29535.47 29336.98 29434.29 29434.29
330'431 331-432
29430.97 (+0.07) 29430.97
303 - 404 312 ~413 313 -
414
36795.92 (-0 03) 36671.10 (-0.04) 36919 24 (-0 03)
404 - 505 414-515 413 -, 514 42?. + 523
423-'524 432 -+ 533 431 -, 532 440
-
541
441-542
(-0.06) (-0 05) (-0.03) (+0.03) (-0 03)
obs
-.._--._-----~
obs -talc
29607.53 (-0.24) 29707 50 (-0.03) 29506.80 (+0.03)
37006.42 (tO.O1)
36792.81
(+O.ll)
3678862
(+O.lO)
36788.62
(+0
37006.42 37002.16 37002.16
(t0.15) (+O.ll) (+O.ll)
36996.0 36995.0
(-0.08) (-0.08)
10)
Carbon-atom scrambling was immediately evident when it was observed that S-UC-1 by pyrolysis produces not onIy IV, but also small quantities of III. This phenomenon was put on a semi-quantitative basis by measuring the intensity of the 414-3-5 15 transltion of IV at 37928.76 MHz and of the 4,+5, transition of III at 36671 .I0 MHz as a functron of oven temperature (450-700°C). The spectrometer square-wave voltage, the detector crystal current (5 PA), the gain of the phase-sensitive detector and the pen recorder, were kept constant under constant frequency sweep rate etc. The pressure at the spectrometer entrance for Table 3 Ground-state
rotational
Species
constants (m hIHz) and distortion
____--___303 - 404 3 12 -+413 313 ‘414 322 -f 423 3zt - 422
37009 52 (-0.03) 36883.30 (-0 02) 37134.32 (+O 03)
1 March 1981
Table 2 Ground-state, + rotational transitions in MHz of gaseous 12CHa =13C=80Se and t2CHa =13C=78Se produced by lowpressure pyrolysis of 5-13C-1.2,3-selenadiazole at 900 K. Microwave cell at room temperature and a total pressure of 15 mTorr (flow system) ---._-___-____ Transition
36792.81 (-0.01)
3678250 (-0.10) 3678250 (-0.10) ---___---________
LETTERS
‘*CHz =r3C=80Se ~___
obs
obs -talc.
ohs,
obs. - talc.
30449.92 30555.50 30343.11 30447.25 30447.25
(-0 08) (-0.04) (-0 04) (+O 06) (-0.01) (+O 06) (+0.06) (-0.07) (-0.03) (-0.03) (-0.01) (~0.13) (t0.11) (+O.ll) (-0.11) (-0.11)
30625.66 30732.42 30517.58 30622 94 30622.94 30619 32 30619 32 38281 93 38146.87 38415.44 38278.63 38278 63 38274.08 38274 08 38267.46 38267.46
(-0.06) (-0.06) (-0.05) (+O 06) (-0.01) (to 06) (+0.06) (-0.06) (-0.05) (-0.04) (-0.01) (+O.lS) (+O.ll) (+O.ll) (-0.1 I) (-0.11)
330-431
30443.66
331-
432
404 +
505
414 413 422 423 432 431-+ 440 44, +
51s 514 523 524 533 532
30443.66 38062.25 37928 76 38194 25 38058.98 38058.98 38054.49 38054.49
541
38047.93
542
r2CHz =raC=7%e --~__-
38047.93 -_---
--~
the gaseous products varied slightly, but it was measured (L K.B _instrument) at each temperature (- 13 mTorr) so that the observed peak intensities could be normalized to constant pressure_ From 450 to 700°C the peak intensrty of the transition at 37928.76 MHZ decreased from 242 to 185 (arbitrary units) while the intensity of the transition at 36671 .lO MHz increased from 3 30 to 7 50 (same scale). A percentage increase in the III/IV concentration ratio from 1.4 to 4.0 1s hereby indicated. Taking differences in half-intensity linewidths into account would seem to change this range to 1 .O-2.7. Due to thrs temperature dependence
constants (in kHz) of fonr rsotopic species of selenoketene ____ --.-_ -
A0 a)
Bo
CO
*J
*DC
'3CH2=12C=7sSe
280390 280460
3704.453~Oo.015 3726.097iO.014
3654.827+0.015 3675.904~0.014
0.64r0.27 0.64@
85.1
12CH2 =‘3C=SoSe
280410
3832.833 & 0.017
3779.735 F 0.017
0.73 * 0.30
90.32 2 0.48
‘2CHz=13C=78Se
280410
3855_101*
3801.388 + 0.017
0 60 + 0.31
91.20 2 0.49
___-________-_-13CHz =x~C=goSe
a) Determined b, Frxed. 302
0.017
by arbitrarily assuming an inertial defect I, - lb -1,
= 0.05 tiz
(l,(ua”>
= 505376/A
(MHz),
84.36eOo.43
etc.).
f 0.6
CHEMICAL PHYSICS LETTERS
Volume 78, number 2
Table 4 Structure of selenaketene (distances in A, angles in deg). I: revised rs structure, this work, and II: idealized StnwtUre USed in an “‘ab initro” calculation [7] II
f r (C&e) r
1.698 1.311 1.090
119.7
1.71 1.31 108 120
the occurrence of III cannot be due to “contamination” of 5-i3C-I by a few percent 4-13C-I (rmprobable per se)_ The velocity increase by mcreasing temperature clearly points to some chemical process(es). Faster pumping at lower pressure, and slower pumping at higher pressure were of no consequence, thus speaking in dlsfavour of bi-molecular mechanisms_
1 March 1981
of I at 547*C i8] showed peaks expected for II at mass numbers 102-108. This pattern could Involve contributions from V, but its complexity may, in part, be due to HC=C=%e, C=C=80Se, etc. No photoionization spectrum of V was obtained [S] . Decomposition reactions are obvious themes for advanced theoretical treatment such as in a recent paper on CH3CH2F -+ CH,=CH, f HF [9]. A priori knowledge of intermediates and final products will, of course, limit the choice of “reaction coordinates” considerably. It must facilitate such treatments that slmrlar reaction paths for different molecules such as I ,2,3thiadiazole and 1,2,3seIenadiazole are suggested by experimental findings. Distinction between the “irene” intermediate as a metastabie product or a transrtionstate conformation (structure) may be trivial to a first approximation.
Acknowledgement 2. Discussion Intermediate three-membered ring formation during photo- and pyre-Iysis of cychc diazoles has attracted considerable attention [4] _Thus, 1,2,3-thiadiazole (Vi), the sulphur analogue of I, photolyzes at 8 K to thioketene (VII), HCZC-SH (VIII), and thiuene (IX), the analogue of V, as evidenced by IR absorption spectra and a normai-coordinate treatment of observed vibrational frequencies [5,6] _Therefore, IX is a metastable species. By pyrolysis at 800°C [7] of 4- and 5-13C-VI (MW detection) 10% “CH,=13C=S and 10% 13CH2=12C=S were formed, respectively, as confumatory evidence for the role of IX either as a metastable species or a transition-state conformation. Neither IX (nor VIII) coufd be observed in the MW spectrometer
E71.
Photolysls of I at 8 K has produced V as a metastable species (tentatively interpreted from an IR spectrum) [S ] . The occurrence of Be scrambling of I3 C&belled I during pyrolysis may likewise be taken as conf%matory evidence for the role of V as a metastable species or a transition-state conformation. Again, neither V nor HCEC-80Se-H could be observed in the MW spectrum. The mass spectrum of the pyrolytic products
G-0. Sorensen of Chemical Laboratory
V is thank-
ed for his permission to use his ROTFKT program.
The Danish Research Council for Natural Sciences has supported thrs work.
References 111 B. Bak, 0. Niefsen, H. Svanhoit and A. Ho&r, Chem. Phys
Letters 53 (1978) 374. [Z] B. Bak, 0. Nielsen, H. Svanholt and A. HoIm, Chem. Pbys. Letters 55 (1978) 36. [3] L. LaIezari, A. Shaffiee and M. Yalpani, J. Org. Chem. 36 (1971) 2876. [4] U:$nm, Li. MerkIe and H Meier, Chem. Ber. 113 (1980) [S] A. &ntz and J. Laurenr, J. Org. Chem, 44 (1979) 2’730, and references therein. [6] M. Torree, J. Safarik, A. Clement, J.E. Bertie and 0 P. Strausz, Nouv. J. Chim. 3 (1979) 365. 17 J B. Bak, 0. NreIsen, H. Svanholt, A. Hahn, N.H. Toubro, A. Kmntz and J. Laureni, Acta Cbem. &and. A33 (1979) 161. [S] H. Bock, S. Aygen, P. Rosmus and B. Solo&i, Chem. Ber. 113 (1980) 3187. [9] S. Kato and K. Morokuma, 3. Chem. Phys. 73 (1980) 3900.
303
CHEMICAL PHYSICS UXTERS
Volume 78, number 2
SELENIRENE AS AN ~TE~ED~TE IN THE PYROLYSIS OF 1,2,3SELENADIAZOLE. MZCROWAVE §PECTRA OF 13C LABELLED SELENOKETENE B@rge BAK, Niels A. KRISTIANSEN, Hen& SVANHOLT Chemical Laboratory V. The H.C. orsted Institute, University of Copenhagen, DK-X00 Copenhagen @, Denmark
and Arne HOLM and Steen ROSENKILDE Chemical Laboratory II, The KC. &wed DK-ZOO Copenhagen @, Denmark
Instr’tute, Unwersity
of Copenhagen,
Received24 November 1980 Microwavespectraof ‘3CH~=1iC=s0~78Se and ‘2CH~=*3C=80~78Se fselenoketene)are recorded. By pyrolysis of .5-13C-l ,2,3-selenadiazoleall four speciesare formed. The 13C scramblingmay take place via a threemembered ring, selenirene,but as expected its microwavespectrumwas not observed.
1. Experimental In a “flow” system 1 JJ-selenadiazob (1) pyrolyzes to selenoketene (II) on a hot (SOO-700°C) quartz surface at 10-100 mTorr, conveniently monrtored by microwave (MW) detection 111. By pyrolysis of isotopic species of f structural information on II has been obtained [1,23. MW spectra of 13CH2=12C,80~78Se (III) and %H2= 13C=80~78Se (IV) have now been recorded from 90% ~3C-enriched samples of 4-13C-I (w 5 mg) and 5-U C-I (R 10 mg). Hereby an earlier minor ambiguity in the published selenoketene “substitution” structure has been removed 121. However, the main
““I
N
‘35 \-iii
I 532-I
Fig.
1.
purpose of this paper is to provide exp~~rn~nta~ MW transrrzon frequencies and intensities of HI and IV for examination of possrble carbon-atom scmmbling when vapor of I passes the hot zone converting, for example, as sketched in fig. 1. 4-13C-I and 5-u C-i were prepared f3] from 90% UC-enriched 12CH3UCH20H and I3 C& ‘2CH,0H, respectively. The recorded MW spectra of III and IV are given in tables 1 and 2, +JBe appropriate rotational and distortion constants are reported in table 3, The final “substitution” structure of II now based on enriched species throughout is presented in table 4, not calling for further comments than already given in ref. f2] .
As-
Ez
8os’e
s&
1
1 5L
Possibiereaction path for 5-‘3C-1,2,3-se~enadiazohto CHa =13C=Se
selenireue0
H”
.
m
(IHI throughan intermediate
duringpyroiysis.
0 OOQ-2614/81/0000-0000/$02.50
0 North-Holland
Publishing Company
301
Volume
CHEhIICAL
78, number 2
PHYSICS
Table 1 Ground-state,
Joerotational transitions in MHz ofgaseous 13CH2 =12C=80Se and 13CH2 =l*C= 78Se produced by lowpressure pyrolysis of 4-i3C-1 .2,3-selenadiazole at 900 K. Mrcrowaye ceil at room temperature and a total pressure of 15 mTorr (flow system) c____._.._._ _-...-. .-. --. --
ohs. ._--_____--_
--_
*3CH2=‘2C=78Se
r3C& =‘2C,80Se
Transtion
obs. - talc _.-.
322 - 423 32r422
29436 83 29535.47 29336.98 29434.29 29434.29
330'431 331-432
29430.97 (+0.07) 29430.97
303 - 404 312 ~413 313 -
414
36795.92 (-0 03) 36671.10 (-0.04) 36919 24 (-0 03)
404 - 505 414-515 413 -, 514 42?. + 523
423-'524 432 -+ 533 431 -, 532 440
-
541
441-542
(-0.06) (-0 05) (-0.03) (+0.03) (-0 03)
obs
-.._--._-----~
obs -talc
29607.53 (-0.24) 29707 50 (-0.03) 29506.80 (+0.03)
37006.42 (tO.O1)
36792.81
(+O.ll)
3678862
(+O.lO)
36788.62
(+0
37006.42 37002.16 37002.16
(t0.15) (+O.ll) (+O.ll)
36996.0 36995.0
(-0.08) (-0.08)
10)
Carbon-atom scrambling was immediately evident when it was observed that S-UC-1 by pyrolysis produces not onIy IV, but also small quantities of III. This phenomenon was put on a semi-quantitative basis by measuring the intensity of the 414-3-5 15 transltion of IV at 37928.76 MHz and of the 4,+5, transition of III at 36671 .I0 MHz as a functron of oven temperature (450-700°C). The spectrometer square-wave voltage, the detector crystal current (5 PA), the gain of the phase-sensitive detector and the pen recorder, were kept constant under constant frequency sweep rate etc. The pressure at the spectrometer entrance for Table 3 Ground-state
rotational
Species
constants (m hIHz) and distortion
____--___303 - 404 3 12 -+413 313 ‘414 322 -f 423 3zt - 422
37009 52 (-0.03) 36883.30 (-0 02) 37134.32 (+O 03)
1 March 1981
Table 2 Ground-state, + rotational transitions in MHz of gaseous 12CHa =13C=80Se and t2CHa =13C=78Se produced by lowpressure pyrolysis of 5-13C-1.2,3-selenadiazole at 900 K. Microwave cell at room temperature and a total pressure of 15 mTorr (flow system) ---._-___-____ Transition
36792.81 (-0.01)
3678250 (-0.10) 3678250 (-0.10) ---___---________
LETTERS
‘*CHz =r3C=80Se ~___
obs
obs -talc.
ohs,
obs. - talc.
30449.92 30555.50 30343.11 30447.25 30447.25
(-0 08) (-0.04) (-0 04) (+O 06) (-0.01) (+O 06) (+0.06) (-0.07) (-0.03) (-0.03) (-0.01) (~0.13) (t0.11) (+O.ll) (-0.11) (-0.11)
30625.66 30732.42 30517.58 30622 94 30622.94 30619 32 30619 32 38281 93 38146.87 38415.44 38278.63 38278 63 38274.08 38274 08 38267.46 38267.46
(-0.06) (-0.06) (-0.05) (+O 06) (-0.01) (to 06) (+0.06) (-0.06) (-0.05) (-0.04) (-0.01) (+O.lS) (+O.ll) (+O.ll) (-0.1 I) (-0.11)
330-431
30443.66
331-
432
404 +
505
414 413 422 423 432 431-+ 440 44, +
51s 514 523 524 533 532
30443.66 38062.25 37928 76 38194 25 38058.98 38058.98 38054.49 38054.49
541
38047.93
542
r2CHz =raC=7%e --~__-
38047.93 -_---
--~
the gaseous products varied slightly, but it was measured (L K.B _instrument) at each temperature (- 13 mTorr) so that the observed peak intensities could be normalized to constant pressure_ From 450 to 700°C the peak intensrty of the transition at 37928.76 MHZ decreased from 242 to 185 (arbitrary units) while the intensity of the transition at 36671 .lO MHz increased from 3 30 to 7 50 (same scale). A percentage increase in the III/IV concentration ratio from 1.4 to 4.0 1s hereby indicated. Taking differences in half-intensity linewidths into account would seem to change this range to 1 .O-2.7. Due to thrs temperature dependence
constants (in kHz) of fonr rsotopic species of selenoketene ____ --.-_ -
A0 a)
Bo
CO
*J
*DC
'3CH2=12C=7sSe
280390 280460
3704.453~Oo.015 3726.097iO.014
3654.827+0.015 3675.904~0.014
0.64r0.27 0.64@
85.1
12CH2 =‘3C=SoSe
280410
3832.833 & 0.017
3779.735 F 0.017
0.73 * 0.30
90.32 2 0.48
‘2CHz=13C=78Se
280410
3855_101*
3801.388 + 0.017
0 60 + 0.31
91.20 2 0.49
___-________-_-13CHz =x~C=goSe
a) Determined b, Frxed. 302
0.017
by arbitrarily assuming an inertial defect I, - lb -1,
= 0.05 tiz
(l,(ua”>
= 505376/A
(MHz),
84.36eOo.43
etc.).
f 0.6
CHEMICAL PHYSICS LETTERS
Volume 78, number 2
Table 4 Structure of selenaketene (distances in A, angles in deg). I: revised rs structure, this work, and II: idealized StnwtUre USed in an “‘ab initro” calculation [7] II
f r (C&e) r
1.698 1.311 1.090
119.7
1.71 1.31 108 120
the occurrence of III cannot be due to “contamination” of 5-i3C-I by a few percent 4-13C-I (rmprobable per se)_ The velocity increase by mcreasing temperature clearly points to some chemical process(es). Faster pumping at lower pressure, and slower pumping at higher pressure were of no consequence, thus speaking in dlsfavour of bi-molecular mechanisms_
1 March 1981
of I at 547*C i8] showed peaks expected for II at mass numbers 102-108. This pattern could Involve contributions from V, but its complexity may, in part, be due to HC=C=%e, C=C=80Se, etc. No photoionization spectrum of V was obtained [S] . Decomposition reactions are obvious themes for advanced theoretical treatment such as in a recent paper on CH3CH2F -+ CH,=CH, f HF [9]. A priori knowledge of intermediates and final products will, of course, limit the choice of “reaction coordinates” considerably. It must facilitate such treatments that slmrlar reaction paths for different molecules such as I ,2,3thiadiazole and 1,2,3seIenadiazole are suggested by experimental findings. Distinction between the “irene” intermediate as a metastabie product or a transrtionstate conformation (structure) may be trivial to a first approximation.
Acknowledgement 2. Discussion Intermediate three-membered ring formation during photo- and pyre-Iysis of cychc diazoles has attracted considerable attention [4] _Thus, 1,2,3-thiadiazole (Vi), the sulphur analogue of I, photolyzes at 8 K to thioketene (VII), HCZC-SH (VIII), and thiuene (IX), the analogue of V, as evidenced by IR absorption spectra and a normai-coordinate treatment of observed vibrational frequencies [5,6] _Therefore, IX is a metastable species. By pyrolysis at 800°C [7] of 4- and 5-13C-VI (MW detection) 10% “CH,=13C=S and 10% 13CH2=12C=S were formed, respectively, as confumatory evidence for the role of IX either as a metastable species or a transition-state conformation. Neither IX (nor VIII) coufd be observed in the MW spectrometer
E71.
Photolysls of I at 8 K has produced V as a metastable species (tentatively interpreted from an IR spectrum) [S ] . The occurrence of Be scrambling of I3 C&belled I during pyrolysis may likewise be taken as conf%matory evidence for the role of V as a metastable species or a transition-state conformation. Again, neither V nor HCEC-80Se-H could be observed in the MW spectrum. The mass spectrum of the pyrolytic products
G-0. Sorensen of Chemical Laboratory
V is thank-
ed for his permission to use his ROTFKT program.
The Danish Research Council for Natural Sciences has supported thrs work.
References 111 B. Bak, 0. Niefsen, H. Svanhoit and A. Ho&r, Chem. Phys
Letters 53 (1978) 374. [Z] B. Bak, 0. Nielsen, H. Svanholt and A. HoIm, Chem. Pbys. Letters 55 (1978) 36. [3] L. LaIezari, A. Shaffiee and M. Yalpani, J. Org. Chem. 36 (1971) 2876. [4] U:$nm, Li. MerkIe and H Meier, Chem. Ber. 113 (1980) [S] A. &ntz and J. Laurenr, J. Org. Chem, 44 (1979) 2’730, and references therein. [6] M. Torree, J. Safarik, A. Clement, J.E. Bertie and 0 P. Strausz, Nouv. J. Chim. 3 (1979) 365. 17 J B. Bak, 0. NreIsen, H. Svanholt, A. Hahn, N.H. Toubro, A. Kmntz and J. Laureni, Acta Cbem. &and. A33 (1979) 161. [S] H. Bock, S. Aygen, P. Rosmus and B. Solo&i, Chem. Ber. 113 (1980) 3187. [9] S. Kato and K. Morokuma, 3. Chem. Phys. 73 (1980) 3900.
303