A study of the vacuum pyrolysis of 6,6-dihalobicyclo[3.1.0]hexanes with Hel ultraviolet photoelectron spectroscopy

1994 ◽  
Vol 72 (12) ◽  
pp. 2537-2539 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Chandra Deo Roy ◽  
Jiangong Ma
Keyword(s):  
Heat Source ◽  
Gas Phase ◽  
High Power ◽  
Photoelectron Spectroscopy ◽  
Laser Power ◽  
Continuous Wave ◽  
Spectroscopic Studies ◽  
High Yield ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Vacuum Pyrolysis

To establish the utility of using a high-power CW (continuous wave) CO2 laser as a directed heat source for preparing organic transients targeted for gas-phase ultraviolet photoelectron spectroscopic studies, we studied the vacuum pyrolysis of 6,6-dibromobicyclo[3.1.0]hexane (1a), 6,6-dichlorobicyclo[3.1.0]hexane (1b), and exo-6-bromo-endo-6-chlorobicyclo[3.1.0]hexane (1c). While it has already been established that 1a and 1b rearrange to the 2,3-dihalocyclohexenes 3a and 3b, respectively, when heated in the condensed phase, upon vacuum pyrolysis 1a and 1b readily eliminate HX — not the dihalogens — and give the 2-halo-1,3-cyclohexadienes 2a and 2b in high yield. That 2,3-dibromocyclohexene (3a) does not eliminate HBr at the laser power used to pyrolyze 1a and 1b and that bromochloro compound 1c selectively loses HCl to form 2a suggests that the 1,3-elimination of HX occurs in a concerted fashion without isomerization of the cyclopropane.

A study of the vacuum pyrolysis of 4-diazo-3-isochromanone with Hel ultraviolet photoelectron spectroscopy

1995 ◽  
Vol 73 (10) ◽  
pp. 1738-1740 ◽  
Author(s):  
N.H. Werstiuk ◽  
J. Ma ◽  
C.D. Roy ◽  
A.J. Kresge ◽  
E. Jefferson
Keyword(s):  
Mass Spectrometry ◽  
Heat Source ◽  
Photoelectron Spectroscopy ◽  
Laser Power ◽  
Ring Opening ◽  
Power Level ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Photoionization Mass Spectrometry ◽  
Cw Laser ◽  
Vacuum Pyrolysis

A newly developed ultraviolet photoelectron spectrometer – CO2 laser instrument that utilizes a 50-W CW laser as a directed heat source was used to study the vacuum pyrolysis of 4-diazo-3-isochromanone (1). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy and photoionization mass spectrometry established that 1 undergoes a facile, unexpected pyrolysis at a laser power level of 26 W yielding N2, CO, and benzocyclobutenone (6). A multistep mechanism beginning with the formation of 4-carbena-3-isochromanone (2), which rearranges to oxaketene 3, can be written for the reaction. If 3 is an intermediate, it must be unusually thermally labile for it readily decarbonylates to 2-carbena-3,4-benzotetrahydrofuran (4). The ring opening of 4 into the ortho-quininoid ketene 5 and the cyclization of 5 into 6 are possible final steps in the conversion of 1 into 6. Keywords: vacuum pyrolysis, 4-diazo-3-isochromanone, HeI ultraviolet photoelectron spectroscopy.

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

1996 ◽  
Vol 74 (12) ◽  
pp. 2536-2539 ◽  
Author(s):  
N.H. Werstiuk ◽  
J. Ma ◽  
C.D. Roy ◽  
A.J. Kresge ◽  
E.A. Jefferson
Keyword(s):  
Heat Source ◽  
Ab Initio ◽  
Photoelectron Spectroscopy ◽  
Laser Power ◽  
Activation Enthalpy ◽  
Power Level ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Wolff Rearrangement ◽  
Vacuum Pyrolysis ◽  
New Compounds

A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO2 laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one (1a). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that 1a undergoes a facile pyrolysis at a laser power level of less than 26 W, yielding two new compounds: thiaketene 3a, the product of a Wolff rearrangement, and benzocyclobutenthione (6a), which can be derived from thiacarbene 4a, the decarbonylation product of 3a. Activation enthalpies/energies calculated at the AM1 and ab initio levels of theory indicate that, unlike the case of 4-diazoisochroman-3-one (1b), the Wolff rearrangement of the incipient carbene may be concerted with loss of nitrogen from 1a. The activation enthalpy/energy calculated for the decarbonylation of 3a is significantly higher (AM1, 20.5 kcal/mol; RHF/6-31G(d), 11.7 kcal/mol; MP2(full)//RHF/6-31G(d), 14.3 kcal/mol) than the activation enthalpy/energy for the decarbonylation of 3b. This result is in keeping with the fact that we detect 3a, but 3b is not found in detectable amounts in the pyrolysate of 1b. Key words: vacuum pyrolysis, 4-diazoisothiochroman-3-one, HeI ultraviolet photoelectron spectroscopy, AM1 and ab initio calculations.

scholarly journals A study of the vacuum pyrolysis of para-substituted diazoacetophenones with He(I) ultraviolet photoelectron spectroscopy

1998 ◽  
Vol 76 (8) ◽  
pp. 1162-1173 ◽  
Author(s):  
Nick H Werstiuk ◽  
Heidi M Muchall ◽  
Jiagong Ma ◽  
Michael TH Liu
Keyword(s):  
Photoelectron Spectroscopy ◽  
Quantum Chemical ◽  
Laser Power ◽  
Spectroscopic Data ◽  
Power Level ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Wolff Rearrangement ◽  
Vacuum Pyrolysis ◽  
The Subject ◽  
Ab Inito

An ultraviolet photoelectron (PE) spectrometer apparatus that utilizes a tuneable 50 W CW CO2 laser as a directed heat source was used to study the vacuum pyrolysis of diazoacetophenone (1a) and its p-methyl, p-methoxy, p-chloro, and p-nitro analogues 1b, 1c, 1d, and 1e. Analysis of the pyrolysate with He(I) ultraviolet PE spectroscopy shows that at a laser power level of 26 W (500 ± 50°C) 1a, 1b, 1c, and 1d, cleanly yield the corresponding phenylketenes 2a, 2b, 2c, and 2d, respectively, the products of the Wolff rearrangement of the incipient ketocarbenes. Of this group of highly reactive ketenes, which cannot be isolated in the condensed phase at ambient temperature, only 2a has been the subject of a previous PE spectroscopic study. But our work indicates that the sample of 2a prepared in the earlier study was impure. The low volatility of p-nitrodiazoacetophenone (1e) thwarted our attempts to generate 2e and obtain its spectrum. Calculations at semiempirical (AM1) and ab inito (HF/6-31G(d)) levels of theory established that the diazoacetophenones prefer to adopt twisted syn conformations. That the calculated ionization potentials (HAM/3 and Becke3LYP/6-31+G(d)//HF/6-31G(d)) of 1a-1d and the synthesized PE spectra of 1a, 1b, and 1c correlate well with the PE spectroscopic data supports this finding. Shifts observed in the three low-energy ionizations of ketenes 2b, 2c, and 2d induced by the para-substitution can be related to the character of the corresponding occupied molecular orbitals of phenylketene (2a).Key words: diazoacetophenones, phenylketenes, He(I) photoelectron spectroscopy, thermolysis, quantum chemical calculations.

scholarly journals Thermolysis of 2,2-dimethoxy-5,5-dimethyl- Δ3- 1,3,4- oxadiazoline studied with photoelectron spectroscopy. He(I) photoelectron spectrum of dimethoxycarbene

1998 ◽  
Vol 76 (2) ◽  
pp. 238-240
Author(s):  
H M Muchall ◽  
N H Werstiuk ◽  
B Choudhury ◽  
J Ma ◽  
J Warkentin ◽  
...  
Keyword(s):  
Heat Source ◽  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Photoelectron Spectrum ◽  
Ionization Potentials ◽  
Perfect Agreement ◽  
Dimethyl Oxalate ◽  
Orbital Energies ◽  
Vertical Ionization Potentials ◽  
Experimental Values

Gas phase thermolysis of 2,2-dimethoxy-5,5-dimethyl- Δ3-1,3,4-oxadiazoline (1) in an ultraviolet photoelectron spectrometer by means of a CW CO2 laser as directed heat source at 26 W gave a complex PE spectrum that included ionization bands belonging to acetone, tetramethoxyethylene (3), and dimethyl oxalate (4). Subtraction of the spectra of acetone, 3, and 4 from the pyrolysis spectrum of 1 left a simple PE spectrum that is attributed to dimethoxycarbene (2) along with some ethane. ecke3LYP/6-31+G* calculations gave first adiabatic and vertical ionization potentials of 2 as well as orbital energies that are in perfect agreement with experimental values. From the available experimental and calculational data, 2 is assumed to adopt a w conformation.Key words: dimethoxycarbene, 2,2-dimethoxy- Δ3-1,3,4-oxadiazoline, tetramethoxyethylene, He(I) photoelectron spectroscopy, thermolysis.

Gas phase flash pyrolysis of 3-azido-1,2,4-triazole: generation and ultraviolet photoelectron spectrum of N-cyanomethanimine

1988 ◽  
Vol 66 (9) ◽  
pp. 2123-2129 ◽  
Author(s):  
I. B'Shary ◽  
C. Guimon ◽  
M. Grimaud ◽  
G. Pfister-Guillouzo ◽  
D. Liotard
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Photoelectron Spectrum ◽  
Reaction Path ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Pyrolysis Gas ◽  
Flash Pyrolysis ◽  
Ionic States ◽  
Configuration Interaction Calculations

A dimer of HCN, N-cyanomethanimine 6, was prepared by flash pyrolysis (gas phase, 10−2 mbar) from 3-azido-1,2,4-triazole 1a and detected by ultraviolet photoelectron spectroscopy (HeI). Its ionization potentials were measured and the ionic states sequence proposed, with the aid of ab initio – CI (configuration interaction) calculations. The study of the MNDO potential hypersurface enabled us to propose a mechanism of the thermal reorganization of the precursor 1a. It is shown that the reaction path passes through the formation of the protomer 1b before thermal decomposition and the generation of the nitrene 2b.

Synthesis and Microwave Spectroscopic Study of Fluorinated Methyl Isocyanides

1994 ◽  
Vol 49 (6) ◽  
pp. 703-708 ◽  
Author(s):  
M. Krüger ◽  
H. Dreizler ◽  
D. Lentz ◽  
D. Preugschat
Keyword(s):  
Stark Effect ◽  
Continuous Wave ◽  
Spectroscopic Studies ◽  
Coupling Constants ◽  
Rotational Spectrum ◽  
Flash Vacuum Pyrolysis ◽  
Microwave Spectrometer ◽  
Vacuum Pyrolysis ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole

Abstract Difluoromethyl isocyanide has been generated by flash vacuum pyrolysis of pentacarbonyl (di-fluoromethyl isocyanide) chromium at 240 °C. Spectroscopic studies revealed the presence of several major and minor impurities like HCN, HCC -CN and HCC -NC . The pyrolysis of pentacarbonyl (fluoromethyl isocyanide)chromium did not lead to the observation of free fluoromethyl isocyanide. The rotational spectrum of difluoromethyl isocyanide has been recorded with a conventional continuous wave Stark spectrometer and a molecular beam Fourier transform microwave spectrometer resulting in A = 10.110841 (42), B = 4.550914 (19), C = 3.343550 (19) GHz, D′J = 0.41(13), D′JK = 26.72(36), D′J = - 21.3 (18) kHz. The dipole moment components μa = 1.46(1), μc= 1.83 (1) and μtotal 2.34 (1) D were obtained from the second order Stark effect. The 14N nuclear quadrupole hyperfine structure in the rotational spectrum of CHF2-NC has been resolved and the 14N nuclear quadrupole coupling constants xaa = 599.0 (10), xbb = −406.5 (14), xcc= −192.6 (14) kHz have been obtained.

Gas-Phase Thermolysis of 4-Substituted 3,5-Dihydro-3,3,5,5-tetramethyl-4H- pyrazoles Studied by Photoelectron Spectroscopy and Flash Vacuum Pyrolysis

1990 ◽  
Vol 123 (5) ◽  
pp. 1161-1168 ◽  
Author(s):  
Markus K. Kindermama ◽  
Rainer Poppek ◽  
Paul Rademachera ◽  
Andreas Fuß ◽  
Helmut Quast
Keyword(s):  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis
Sign in / Sign up

Export Citation Format

Share Document