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

A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO 2 laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one ( 1 a). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that 1 a u...

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Bibliographic Details
Published in:Canadian journal of chemistry 1996-12, Vol.74 (12), p.2536-2539
Main Authors: Werstiuk, N.H, Ma, J, Roy, C.D, Kresge, A.J, Jefferson, E.A
Format: Article
Language:English
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Summary:A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO 2 laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one ( 1 a). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that 1 a undergoes a facile pyrolysis at a laser power level of less than 26 W, yielding two new compounds: thiaketene 3 a, the product of a Wolff rearrangement, and benzocyclobutenthione ( 6 a), which can be derived from thiacarbene 4 a, the decarbonylation product of 3 a. Activation enthalpies/energies calculated at the AM1 and ab initio levels of theory indicate that, unlike the case of 4-diazoisochroman-3-one ( 1 b), the Wolff rearrangement of the incipient carbene may be concerted with loss of nitrogen from 1 a. The activation enthalpy/energy calculated for the decarbonylation of 3 a 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 3 b. This result is in keeping with the fact that we detect 3 a, but 3 b is not found in detectable amounts in the pyrolysate of 1 b. Key words: vacuum pyrolysis, 4-diazoisothiochroman-3-one, HeI ultraviolet photoelectron spectroscopy, AM1 and ab initio calculations.
ISSN:0008-4042
1480-3291
DOI:10.1139/v96-285