Thermochemistry of organosilicon compounds

Воронков, М. Г.; Baryshok, V. P.; Klyuchnikov, V.A.; Danilova, T. F.; Pepekin, V. I.; Korchagina, A.N.; Khudobin, Yu. I.

doi:10.1016/0022-328x(88)80231-6

Cited by 42 publications

(9 citation statements)

References 12 publications

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“…There are no tabulated standard enthalpies of formation for the neutral silicon-containing molecules which appear in eqs 7 and 9. The thermochemistry of tetraalkylsilanes now appears to be satisfactory, the enthalpies of formation from the bomb calorimetric results of Voronkov and co-workers being in excellent accord with group additivity estimates, the differences for the different alkyl groups are consistent with those for analogous hydrocarbons, and the value for (CH 3 ) 4 Si is in excellent agreement with the value obtained by Steele …”

Section: Discussionsupporting

confidence: 74%

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

et al. 1996

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The stabilization afforded a vinyl cation by a β-(CH3)3Si substituent has been determined by measuring in a high-pressure mass spectrometer the thermodynamic data for the association of three alkynes (RCCR‘) with (CH3)3Si+ and with the proton. The measured −ΔH° (kcal mol-1) and −ΔS° (in parentheses, cal K-1 mol-1) values for the reaction (CH3)3Si+ + RCCR‘ ⇄ (CH3)3Si·C(R)CR‘+ are as follows: 1-hexyne (R = H, R‘ = n-C4H9) 25.9 ± 1.5 (19.1 ± 0.2), 2-hexyne (R = CH3, R‘ = n-C3H7) 28.8 ± 1.4 (25.5 ± 0.3), and phenylacetylene (R = H, R‘ = C6H5) 28.2 ± 2.8 (16.5 ± 0.4). By comparison the values for 1-hexene which forms an alkyl cation are 38.2 ± 0.5 kcal mol-1 (48.2 ± 0.1 cal K-1 mol-1). The deduced stabilizations (A) for all the substituents (R, R‘ and (CH3)3Si) obtained from the isodesmic reaction (CH3)3Si·C(R)CR‘+ + CH2CH2 → (CH3)3Si·C(R)C(H)R‘ + CH2CH+ are (kcal mol-1) as follows: 1-hexyne 55, 2-hexyne 58, and phenylacetylene 58. The deduced stabilization for the (CH3)3Si+ adduct of 1-hexene relative to the ethyl cation is 60 kcal mol-1. The measured proton affinities are (kcal mol-1) as follows: 1-hexyne 194.5 ± 0.5, 2-hexyne 195.8 ± 0.2, phenylacetylene 198.6 ± 0.2, and 1-hexene 194.0 ± 0.5. The stabilizations (B) due to R and R‘ in the vinyl cations RC(H)CR‘+ produced by protonaton are calculated from the isodesmic reactions RC(H)CR‘+ + CH2CH2 → RC(H)C(H)R‘ + CH2CH+ and are (kcal mol-1) as follows: 1-hexyne 44, 2-hexyne 46, and phenylacetylene 50. The comparable value for the alkyl cation from the protonation of 1-hexene is 34 kcal mol-1. The stabilizations of the vinyl cations RC(H)CR‘+ due to the presence of a β-(CH3)3Si (A − B) are (kcal mol-1) as follows: 1-hexyne 11, 2-hexyne 12, and phenylacetylene 9. For the alkyl cation formed from 1-hexene, the value is 26 kcal mol-1. The stabilization of a vinyl cation by an α-alkyl or α-aryl substituent is subtantially greater than that afforded by the same substituent in an alkyl cation. The total stabilization afforded by both an α-alkyl or α-aryl substituent and a β-(CH3)3Si substituent appears to be approximately the same in both alkyl and vinyl cations and hence the β-silicon effect is considerably smaller for the vinyl cation.

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Section: Discussionsupporting

confidence: 74%

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

et al. 1996

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“…Walsh21 lists heats of formation for 12 silanol, siloxane, or silyl ether species in his 1989 review of thermochemistry of organic silicon compounds, four of which overlap with the present study. Voronkov et al 22 reported thermochemical data from rotating-bomb calorimetry studies for a large number of tetracoordinate silicon compounds in 1988. These studies include over 30 Si-O-H-C compounds, but most are too large for our theoretical methods.…”

Section: Resultsmentioning

confidence: 99%

Theoretical Study of the Thermochemistry of Molecules in the Si-O-H-C System

Ho¹,

Melius²

1995

J. Phys. Chem.

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A self-consistent set of thermochemical parameters for more than 30 molecules in the Si-0-H-C system are obtained from a combination of ab initio electronic structure calculations and empirical corrections. Heats of formation are estimated for another 15 species. The species are primarily methoxy-and ethoxysilicon compounds, including both stable and radical species as well as a few transition states. In the few cases where comparisons with experimental data in the literature are possible, there is good agreement with the calculated values. The energetics of Si(OC2H5)4 (TEOS) decomposition reactions show that it is likely to decompose via the four-center elimination of ethylene while Si(OCH& decomposes via different reactions. This thermochemical and kinetic information will advance the modeling of the chemical vapor deposition of silicon oxide films from Si(OC2H5)4.

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“…where R sample and R ref are the GC-C-IRMS measured 13 C/ 12 C ratios of the sample and reference gas CO 2 peaks, respectively. The δ 13 C (ref) was corrected for 17 O contributions. Because the reference tank gas had been standardized to PDB, the δ 13 C (ref) was converted to a delta value referenced to PDB (δ 13 C (PDB) ).…”

Section: Methodsmentioning

confidence: 99%

Retention of Carbon and Alteration of Expected ¹³C-Tracer Enrichments by Silylated Derivatives Using Continuous-Flow Combustion-Isotope Ratio Mass Spectrometry

2002

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Continuous-flow inlets from oxidation reactors are commonly used systems for biological sample introduction into isotope ratio mass spectrometers (IRMS) to measure 13C enrichment above natural abundance. Because the samples must be volatile enough to pass through a gas chromatograph, silylated derivatization reactions are commonly used to modify biological molecules to add the necessary volatility. Addition of a tert-butyldimethylsilyl (TBDMS) group is a common derivatization approach. However, we have found that samples do not produce the expected increment in measured 13C abundance as the TBDMS derivatives. We have made measurements of 13C enrichment of leucine and glutamate standards of known 13C enrichment using derivatives without silicon (N-acetyl n-propyl ester), with silicon (TBDMS), and an intermediate case. The measurements of 13C in amino acids derivatized without silicon were as expected. The 13C enrichment measurements using the TBDMS derivative were higher than expected but could be corrected to produce the expected 13C enrichment measurement by IRMS if one carbon was removed per silicon. We postulate that the silicon in the derivative forms silicon carbide compounds in the heated cupric oxide reactor, rather than forming silicon dioxide. Doing so reduces the amount of CO2 formed from the carbon in the sample. Silylated derivatives retain carbon with the silicon and must be used carefully and with correction factors to measure 13C enrichments by continuous-flow IRMS.

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Thermochemistry of organosilicon compounds

Cited by 42 publications

References 12 publications

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

Theoretical Study of the Thermochemistry of Molecules in the Si-O-H-C System

Retention of Carbon and Alteration of Expected ¹³C-Tracer Enrichments by Silylated Derivatives Using Continuous-Flow Combustion-Isotope Ratio Mass Spectrometry

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Thermochemistry of organosilicon compounds

Cited by 42 publications

References 12 publications

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

Theoretical Study of the Thermochemistry of Molecules in the Si-O-H-C System

Retention of Carbon and Alteration of Expected 13C-Tracer Enrichments by Silylated Derivatives Using Continuous-Flow Combustion-Isotope Ratio Mass Spectrometry

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Retention of Carbon and Alteration of Expected ¹³C-Tracer Enrichments by Silylated Derivatives Using Continuous-Flow Combustion-Isotope Ratio Mass Spectrometry