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C2H2Si Isomers Generation by Pulsed Flash Pyrolysis and Matrix-Spectroscopic Identification.

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tion in the solid state. Besides the splitting pattern for the signals
of the naphthalene protons, the spectrum exhibits two doublets
and two septets for the two isopropyl groups. At higher temperatures the signals in the aliphatic region coalesce, and at 370K
one doublet and one septet are evident. Compound 5a. in contrast to 5 b, undergoes an exchange process at higher temperatures, in which the two methine protons and the four methyl
groups are equivalent on the N M R timescale. We assume that a
transition state 3 (X = H) is formed by opening of the p-bridge;
both hydrogen atoms of the BH, unit are now capable of forming a new bridge, and thus on the N M R timescale both isopropyl
groups become equivalent. The temperature-dependent
"B NMR spectrum confirms this. At room temperature a slightly
broadened doublet can be seen (coupling of p-H-B is not resolved) which is converted into a quartet at higher temperatures
(370 K). This observation can be explained by the rapid, oscillating motion of the three hydrogen atoms around the boron
atoms, such that they appear equivalent to the boron nucleus.
This phenomenon is comparable to the exchange process of the
hydrogen atoms in p-dimethylaminodiborane(6).['I In this case
the B N M R spectrum displays a doublet of triplets at 283 K
and a sextet at 377K.
[4] W. D. Crow. C. Wentrup. J. Cheiii. Soc. Chem. Conitnun. 1968, 1026, P. Flowerday, M. J. Perkins. J. Chem. Suc. C 1970, 298; D. L. DeJongh. G. N.
Evenson. J. Org. C h i . 1972. 37. 2152.
[5] A. J. Gordon. J Org. Ckem. 1970, 35. 4261 ; D. C. DeJongh, G. N. Evenson.
retrahedroii Left. 1971. 4093.
[6] Crystal structure analysis of 2: triclinic, space group Pi. (I = 8.108(4). h =
14.204(7), c =14.288(7)A. a =74.35(4). 0 =76.08(3). j. =76.04(3) , V =
1510 A' , Z = 4: 4979 independent reflections measured (four-circle dift'ractometer, Mo,, radiation. LU scan); refinement against F* [9] with all reflections,
C , B. and N anisotropic. H atoms isotropic in calculated positions (342
parameters). R1 = 0.066 (for 2350 observed reflections I > 2u(Z)) wR2 =
0.207 (for all reflections) [lo].
[7] Crystal structure analysis o f 5 b : monoclinic, space group P 2 , / n , u = X.762(11).
h=15.35(2). r.=14.20(2)A. / ~ = 9 1 . 5 1 ( 1 0 ) , V=1909A3. Z = 4 : 3329independent reflections measured (four-circle diffractometer. Mo,, radiation. ( t i
scan); refinement q w n s t F' [9] with all reflections, C, B. and N anisotropic, H
atoms isotropic i n calculated positions (230 parameters), R1 = 0.076 (for 1560
observed reflections I 2u(1)) wR2 = 0.217 (for all reflections) [lo]
[XI D. F. Gaines, R. Schaeffer, J. Am. Cheni. So? 1964, 86, 1505; R. E. Schirmer,
J. H. Noggle. D. F. Gaines. ibid. 1969, 91, 6240.
[9] G. M. Sheldrick. SHELXL93, Universitit Gottingen, 1993.
[lo] Further details of the crystal structure investigation may be obtained from the
Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen
(FRG) on quoting the depository numbers CSD-400825 (Z), -400824 (5b).
E>p?rimentulProcedure
2 : A solution of l(28.05 mmol) in ether (70 mL) at - 3 0 ' C was added to a solution
of CI,BNiPr, (84.15 mmol) in hexanes (60 mL) cooled to - 20 C. Filtration and
sublimation (52 C, 0.001 Torr) yielded 2 in 89% yield, m.p. 84 C. 'H NMR
(200 MHz. CDCI,): 6 =7.70 (dd. 2 H ) , 7.60 (dd. 2H). 7.45 (dd. 2 H ) . 3.90 (sept.
2 H ) . 1.47 (d, 12H); i3C NMR (50MHz, CDCI,): d =163 (br.). 148 (br.). 129.4.
126.0. 122 6. 121.8. 49.3. 24.3; "B N M R (29 MHz. CDCI,): 5 = 37; Electron
Impact (EI)-MS: ii1.z ( O h ) : 237 (26) [ M ' ] , 194 (56) [ M i - iPr].
4 a : BCI, was treated with 2 i n hexaiie at -20 C. Workup by recrystallization
provided 4 a in 92% yield. m.p. 89 C (decomp). ' H N M R (200MHz. C,D,):
6=8.49(dd,2H),7.60(dd,2H),7.23(dd,2H).4.96(sept.1H).1.48(d.6H);"C
NMR (75 MHz, C,D,): 6 =139.7. 137.6. 133.8, 126.8. 51.6. 22.6: " B NMR
(29 MHz C,D,): 6 = 43.9: EI-MS:iii,z(%). 275(43)[Mi],260(100)[.Mt
Me].
4 b : Preparation analogous to 4a. yield 53%. m.p. 75 'C (decomp). ' H N M R
-
(300 MHr. CDCI,). 6 = 8.71 (dd, 2H). 8.12 (dd. 2 H ) . 7 66 (dd. 2H). 5.25 (sept,
1 H). 1.73 (d. 6 H ) : ',C NMR (75 MHz. CDCI,): 6 =142.2. 136.5. 133.3. 131.0,
126.2. 55.7. 22.7; "B NMR (29 MHz. CDCI,): 6 = 43.6. El-MS: ni.1 ("1;): 365 (68)
[M'], 350 (100) [.Mi - Me].
5 a : 2 and LiBH, in hexanes were treated with boron trifluoride-ether in ether.
Filtration and recrystallization from hexane yielded 5 a in 93% yield. m.p. 110 C
(decomp). ' H N M R (200 MHz, CDCI,. 220 K ) : 6 =7.76 (dd. 2H). 7 71 (dd. 2 H ) .
7.45 (dd. ZH), 2.7 (sept. br.. 1 H), 2 58 (sept. I H), 2.0 ( b r . ~1 H). 1.49 (d, 6 H ) , 0.98
(d. 6 H ) : 'H NMR (200 MHr. C:D,. 370 K): 6 =7.59 (dd. 2H). 7 51 (dd). 2 H ) .
7.23 (dd. 2 H ) . 2.6s (sept. 2 H ) . 2.0 (hr. 1 H). 0.88 (d. 12H): " C N M R (75 MHz,
C,D,): 6 =146.9. 143 (br.), 131.2. 130.7. 126.9, 126.5-59 (br.). 50 (br 1. 21.8:"B
NMR (64 MHz. C:D,, 270 K); 6 = - 10.3 (d. br.); "B NMR (64 MHz. C-D,.
350 K): 0 = -10.3 (q). El-MS: itir: ("lo):
251 (23) [ M i ] . ?OX (100) [M' - iPr].
5 b : Diethylborane was slowly added to 2 in hexane. 5 b was obtained after recrystallization in 8 2 % yield, m.p. 108 C (decomp). ' H N M R (200 MHz. C,D,): 6 =7.69
(dd.2H).7.61(dd.2H),7.43(dd.2H).3.10(sept,1H),2.77(sept.lH).2.11
(br.
1 H i . 1.3- 1.7 (m.4H). 1.22 ( t . 6 H ) . 1.07 (t. 6H). 0.59 (d. 6 H ) : "C NMR (50 MH7..
C,D,). B =147.4. 144(br.).l31.8. 129.7. 126.9, 126.1, 56.5.51.1,25(br.),23.1. 14.7,
8.X (br.). " B N M R ( 2 9 MHz. C,D,): 6 =1.0; EI-MS: n / : ( % ) : R07(6)[.Mi], 236
(100) [A4 ' - Et - iPr].
4 c : 5 a was treated with ethanol and recrystallized from hexane. Yield . 95%. n1.p.
85 C. ' H N M R ( 2 0 0 MHz.C,D,):d = 8.40(dd,2H).7.72(dd.2H), 7.35(dd,2H).
4.1 (q. br.,4H).?.59(sept. l H ) , 1.23 (t, br..6H).0.90(d. 6 H ) ; " C NMR(5O MHz.
C,D,): 6 =142.3. 134.5. 132.2, 132.0. 125.8, 59(br.).47.9. 18.9, 17(br.): " B N M R
(29 MHz. C,,D,,):S = 29.4.
Receibed: January 29. 1994 [266551E]
German version: ,4ii,yiw Chriii. 1994. 106. 1342
C,H,Si Isomers: Generation by Pulsed Flash
Pyrolysis and Matrix-Spectroscopic Identification**
Giinther Maier," Hans Peter Reisenauer, and
Harald Pacl
The matrix-spectroscopic identification"] and photochemical
interconversion['] of the isomeric carbenes cyclopropenylidene
( I ) , propynylidene (2). and propadienylidene (3) are of interest
in many ways. For one. the isolation of 1-3 as well as their
chlorinatedr2' and fluorinatedr3]derivatives serves to illustrate
the potential of matrix isolation spectroscopy. In addition, the
structural assignments for these species are based on the comparison of the experimentally observed and calculated IR spectra and therefore emphasize the importance of simultaneously
applying quantum chemical calculations and spectroscopic
measurements. Moreover, reactions 1 s2 2 3 are carbene-carbene rearrangements, and only few examples exist for this class
of reactions. Lastly, 1 [41 and 3[51have also been shown to play
a decisive role in the chemistry of interstellar clouds.[61
H
1
2
3
According to calculations by H. E Schifer et al."] 6 is expected
to be the most stable C,H,Si species. Thus, it has been discussed
H. Schwarz et al.
as the adduct of a Si atom with
have shown["] that if one ionizes chlorotrimethylsilane in the
gas phase, neutralization reionization mass spectrometry allows
~
[I] R. W. Hoffmiinn. W. Sieber, Jlurirs Lidq.5 Aiiw. Cheiii. 1967. 703. 96: J. M e n wald. S Knapp, J. A i i i . Chm. Sor,. 1974. 06. 6532.
[2] R. J. Bailey. H. Shechter, J. Am. Climi. S o l . 1974. 96. 8116; M. Gessner. P.
Card. H. Shechter, G. G. Christoph. ibid. 1977, YY. 2371: P. J. Card, F. E.
Friedli. H. Shechter, ihrd. 1983.105.6104;A . Kumar. F, E. Friedli. L . Hsu, P. J.
Card. N. Mathur, H. Shechter. J. Org Chen7. 1991. 56. 1663.
[3] L. S. Yang. H. Shechter, .I Choii. Soc ( ' h w i . Coiiiriiim. 1976, 775.
[*] Prof. Dr. G. Maier. Dr. H. P. Reisenauer. DipLChem. H. P a d
lnstitut fur Organische Chemie der Universitit
Hemrich-Buff-Ring 5 % D-35392 Giessen (FRG)
Telefax: Int. code + (641)702-5712
[**I Hetero A Systems. Part 20. This work was supported by the Fonds der Chemischen lndustrie a n d the Deutsche Forschungsgemeinschaft. -Part 19: ref. 1171
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detection of a particle whose connectivities are indicative of structure 6 .
H\
H
Better experimental access to the C,H,Si potential energy surface is offered by pyrolysis of 2-ethynyl-1,l ,I -trimethyldisilane
(4). Compound 4 can be prepared by reaction of 1,l ,l-trimethyl2-phenyldisilane" 'I with trifluoromethanesulfonic acid (toluene,
4 h, room
to give the corresponding triflate. The
triflate is then treated with mesityllithium (15 min, -40 " C ) to
form 2-mesityl-1.1.1 -trimethyldisilane (44 YO).which upon further reaction with trifluoromethanesulfonic acid (pentane, 4 h,
0 :C)[131and treatment with sodium acetylide (suspension in
diethyl ether) yields 4. The reaction product is distilled under
vacuum and isolated by preparative gas chromatography [silicon phase OV 101, 175'C; yield: 25%; ' H N M R (capillary):
6 = 0.89 (s, 9H. Si(CH,),), 3.00 (t, 4J(H,H) =1.5 Hz, IH.
H-C). 4.34 (d, 4J(H,H) =1.5 Hz, 2H, SiH,); I3C N M R :
S = -1.0 (Si(CHJ3), 80.4 (CSiH,), 98.3 (HC); 29Si N M R :
6 = - 85.7 (SiH,), -16.3 (Si(CHJ3)].
Gaseous mixtures of disilane 4 and argon (1 : 1000-2000) were
subjected to flash pyrolysis at various temperatures and pressures.
After leaving the hot zone the reaction products were directly
condensed onto a CsI or BaF, window at 10 K. The matrix-isolated products were studied by IR and UV/VIS spectroscopy.
Under the conditions of /iigll-vacuuni flash pyrolysis (quartz tube:
diameter 8 mm. length of heated zone 5 cm; ca. 1 O - j mbar,
600 - C ) only trimethylsilane (5) and small amounts of acetylene
were detected. Any C,H,Si isomer that might have formed was
too unstable to be detected under these pyrolysis conditions.
Pulsed flash pyrolysis proved more successful. The gaseous
mixture (regulated by a pulsed magnetic valve) was expanded
through a corundum tube (inner diameter 1 mm, length of heated zone 10 mm, heated to ca. 1100 "C by a tungsten resistance
wire)[14]directly into the high vacuum of the cryostat. The products were condensed onto the matrix window at 10 K.
1986.['"] Furthermore, 6 exhibits a weak, broad UV absorption
between 320 and 260 nm (Ivmax
= 286 nm). Irradiation into this
band with monochromatic light of wavelength 313 nm results in
a rearrangement to give ethynylsilanediyl (7). During this photoreaction only the absorbances of 6 and 7 change, and thus the
IR and UVjVIS spectra of both compounds can be determined
by subtraction. Figure 1 shows the difference IR spectrum and
the calculated spectra for 6 and 7.17a1
II
I
ll
0.1
1
0.0
A
-0.1
3500
-
3000
2500
V
2000
[crn-']
1500
1000
Fig. 1. IR spectra of 6 and 7. Middle: difference IR spectrum for the photoreaction
6 -7 (Ar matrix. 10 K ) . Top: cdlcuhted [7a] IR spectrum for 7 Bottom. calculated
[Fa] IR spectrum for 6 : IR bands due to water have been crossed
Particularly characteristic for 7 are the bands of the C H
(3304.1 cm-I), the CC (1995.5 cm-I), and the SiH (1969.5
cm- ') stretching vibrations. The spectral pattern of the remaining bands at lower wavenumbers (cf. Table 1) is also in satisfactory agreement with the calculation.
Table 1. Experimentally determined IR absorptions (argon matrix. 10 K ) of 6 - 9
([cm- 'I; relative integrated intensities in parentheses).
9
10
6
7
8
9
3048.5 (10)
3026.3 (9)
1085.8 (87)
875.1 (26)
761.8 (56)
677.4 (100)
672.1 (90)
3304.1 (31)
1995.5 (27)
1969.5 (100)
1216.0 (3)
814.8 (49)
722.7 (14)
613.8 (32)
605.1 (41)
1667.5 (100)
957.5 (100)
2228.9 (49)
2214.4 (49)
1769.9 (7)
1023.1 (100)
836.5 (SO)
600.7 (7)
11
Under these pyrolysis conditions the IR spectrum shows, apart
from the bands for trimethylsilane ( 5 ) , those of another compound. This compound is identified as 1-silacyclopropenylidene
(6)-even though the structure of reactant 4 suggests formation
of ethynylsilanediyl (ethynylsilylene) (7)-by comparison with
the IR spectra for 6 , 7, and 8 calculated by a b initio methods in
This is also true for I-silacyclopropenylidene( 6 )(cf. Table 1).
In accordance with the calculation its TR spectrum shows two
bands for the CH stretchmg vibrations (3048.5 and 3026.3 cm- I )
and five additional absorptions between 1100 and 600 cm-',
which, by calculation, can be attributed to HCSi bending vibrations and S i c stretching vibrations. A band for the CC stretching vibration is not observed; theory[7b1predicts a corresponding
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~
band at 1569 cm-' in the IR spectrum with a relative intensity
of < 1 'YO.which is apparently too weak to be detected.
For silanediyl (7) a broad absorption band is recorded in the
visible region of the spectrum (A,,, = 500 nm). It is therefore
not surprising that irradiation of 7 with visible light of wavelength 500 nm mainly leads to reisomerization to give l-silacyclopropenylidene (6).A small amount of a new species is also
formed, and two weak IR bands at 1667.5 and 957.5 cm-' and
a UV band with fine structure (=
i340, 325, and 310 nm) are
recorded. Irradiation into this absorption (2 = 340 nm) leads to
reisomerization to 7; hence, this species is another isomer of
C2H,Si. By comparison with the calculated IR spectra this isomer
is identified as vinylidenesilanediyl (S), for which the strongest
IR band (CC stretching vibration) is predicted at 1859 cmIrradiation of 6 with light of wavelength 1. = 254 nm leads to
the formation of 7 and two new compounds. One of these can
easily be identified by its characteristic IR bands at 1745.3/
1741.0 and 826.4cm-' (ref. [15a-c]: 1741 and 824cm-') and
by its electronic transition band" "I as the well-known,[' 'dl
cyclic C,Si (10). The second compound shows IR absorptions at
2228.9 and 2214.4 cm-', which are typical for SiH, groups (symmetric and asymmetric SiH stretching vibrations). Furthermore,
a weak band at 1769.9 c m - ' and additional bands at 1023.1,
836.5, and 600.7 c m - ' are observed. Therefore, the fourth isomer must either be of constitution 9 or 11. Silacyclopropyne (9)
was initially dismissed as an unlikely candidate, as calculations[7a1indicate that this structure represents a transition state.
Thus. it was important to calculate I R spectra for 9 and 11,
something that had not previously been done. Calculations at
the MP2/6-31G** level["] led to two important findings. Firstly, when the electron correlation energy is taken into account
(cf. Scheme 1) 9 is a minimum. Secondly, the experimentally
i
E/kcalmol-l
63.2
54.4
11
~
9
I
24.8
20.2
0.0
U
7
~
__
8
6
~
11
Schemc 1. Relativeenergies E[kcalmol-'] calculated at the MP2,'6-31G** level for
the isomers 6 - 9 and 11 (energy minima) and optimized geometries (bond lengths
[A] and angles [ 1) for 9 and 11.
measured and calculated spectra are in satisfactory agreement
for 9, but not for 11 (cf. Scheme 1 and Table 2). We therefore
prefer the structure of silacyclopropyne (9) for the fourth isomer.
Table 2 IR absorptions for 9 and I 1 ([cm-'I, absolute intensities [kmmol-'1 in
parentheses) calculated at the MP2/6-31G** level.
9
11
819 (XX)
697 (68)
420 (114)
375 ( 0 )
2371 (148)
2362 (127)
1779 ( < 1 )
1102 (214)
858 (106)
1250
(
Received: January 27. 1994 [Z6651 IE]
German version: Angew. Ckertt. 1994, 1116. 1347
[1] a) H. P. Reisenauer. G. Maier, A. Riemann, R. W. Hoffmann, Angew. Choii.
1984. 96, 596; A n g w . Cliem. Inr. Ed. Engl. 1984, 23, 643; b) G. Maier, H. P.
Reisenauer. W. Schwab. P. &sky, B. A. Hess. Jr.. L. J. Schaad, J. Am. CAm.
Sor. 1987. 109. 5183 -5188; c ) G . Maier. H. P. Reisenauer. W. Schwab. P.
Carsky, V. Spirko. B. A. Hess. Jr.. L. J. Schaad, J. Chen,. Phyy. 1989, 91.
4763-4773.
[2] G . Maier. T. Preiss. H. P. Reisenauer, B. A. Hess, Jr., L. J. Schaad, J .Am.
Chem. So<.. 1994, 116, 2014-2010.
[ 3 ] G. Maier. T. Preiss. H. P. Reisenauer. Chem Ber., 1994. 127. 779- 782.
[4] a) P. Thaddeus. J. M. Vrtilek. C. A. Gottlieb. Asrropyhs. J. 1985, 299. L63L66; b ) N . G . Adams, D. Smith. ibid. 1987. 317. L25-L27
[5] a) J. Cernicharo, C. A. Gottlieb, M. Guelin. T. C. Killian, G. Paubert, P. Thaddeus, J. M. Vrtilek, A.rtrophjs. J. 1991,368, L38-L41; b) C. A. Gottlieb, T C.
Killian, P. Thaddeus. P. Botschwina. J. Flugge. M. Osbald, J. Chrm. PI7ys.
1993, 98,4478-4485.
[6] For the interstellar chemistry of Si-containing molecules, see ref. [lo].
[7] a) G . Frenking. R. B. Remington, H. F. Schdfer 111, J Am. Chem. SOC.1986.
108.2169-2173; b)G. Vacek, B. T. Colgrave. H. F. Schiifer 111, ihrd. 1991.113.
3192-3193 c) For the calculation ofenergies and rotational constants see: D.
L. Cooper. A s r r q d i j n . J 1990, 354, 229-231 : for additional literature see ref
WI.
9
~
This is also supported by the observation that the bands at
1769.9 (CC stretching vibration) and 836.5 cm-' (symmetric
CSi stretching vibration) have similar positions in the C,Si molecule 10 (1 745.3/1741.O and 826.4 cm- l , respectively). The band
at 836.5 cm-' is assigned to the calculated absorption at
858 cm-'. Theory predicts a second, relatively intense band at
819 cin- I . As this absorption is missing in the experimentally
recorded spectrum, the question arises whether further calculations at a higher level are necessary. We will attempt to definitively assign the structure of 9 by studying a 13C isotopomer. To
the best of our knowledge 9 would represent the first example of
a cyclopropyne.
Upon irradiation (A > 395 nm) compound 9 is transformed
into 6 (therefore, both compounds are indeed isomers). Simultaneously, C,Si (lo), which is formed concurrently with 9, reacts
with eliminated hydrogen that is trapped in the same matrix
cage to also give 6. Trapping reactions of this kind have also been
observed for various other unsaturated silicon compounds.['71
2391 (100)
2374 (74)
1967 (345)
1052 (126)
79R (10)
[8] a) D. Husain. P. E. Norris. L Cheni. Soc. Furuduj Truny 2 1978. 74. 106-114:
b) S. C. Basu, D Husian, J Pho/oc/ieni.Phutuhiol. A 1988. 42, 1 - 12.
191 M.-D. Su, R. D. Amos, N. C. Handy, J. .Am. Chem. Soc. 1990. 112.1499-1504.
[lo] R Srinivas. D . Sulale, T. Weiske. H . Schwarz, I n / . J Muss Spe~rrom.Ion
Procrssi~s1991. 107. 369-376.
[I I ] a) E. Hengge. G. Bailer, H. Marketr. Z . Anorg. A&. Cliem. 1972.394.93- 100;
b) D. Littniann. Dissertation, Universitiit GieOen. 1985.
[I21 W. Uhhg, C'hem. 5 ~1992,
. 125, 47-53.
[13] This "detour" is necessary in order to achieve sufficiently different boiling
points during workup between the split-off benzene derivative (mesitylene).
ethynyldisilane (4). and the solvent.
[I41 Pulsing is imperative in order to achieve the high vacuum necessary i n the
matrix apparatus. which is directly flanged to the pyrolysis tube, and to generate a sufficiently high particle density at the moment of pyrolysis so that energy
is not transferred via the wall of the reaction vessel (species 6-9 would stick to
the vessel \*.all) but instead by molecule collisions. Experimental parameters:
duration of pulse. 0 2 s. equivalent to w. 1 mL gas mixture at 1000 mbar per
pulse; pulse frequency: 10 pulses per minute.
[15] a) R. A. Shepherd, W. R. M. Graham, J Chem. Pby.c. 1985, K2, 4788-4790.
b) ibid. 1988.88. 3399 -3401 ;c) W. Weltner. Jr.. D. McLeod. Jr.. ibid. 1964. 41.
235-245, d ) B. Kleman. Aswophys. J. 1956. 123. 162-165.
[16] Gaussian 92. Revision 8 . M. J. Frisch. G. W. Trucks. M. Head-Gordon.
P. M. W. Gill. M . W. Wong, J. B. Foresman. B. G. Johnson. H. B. Schlegel.
M. A. Robb. E. S. Replogle, R. Gomperts, J. L. Andres, K. Raghavachari, J. S.
Binkley. C. Gonzales. R. L. Martin. D. J. Fox, D. J. Defrees, J. Baker. J. J. P.
Stewart. J. A. Peple, Gaussian Inc.. Pittsburgh, PA, USA, 1992.
[17] G. Maier. J. Glatthaar. A n p i ' . Clien?. 1994. f06,486 488; h j i e i v . Ckcm. I f i t .
Ed. Erin/. 1994, 33. 4 7 3 ~475.
690 (78)
684 (73)
122 ( < 1)
120 ( < 1 )
VCH Ver/u~sgrse/ls~liu//
m b H , 0-69451 W<~inheim.
1994
OS70-0833~94~121~-12SO
3 10.00+.2.5;0
Anxew. C/7~m.In/. Ed. Engl. 1994, 33, No. 12
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