Photolysis of gaseous tetramethylethylene between 185 and 230 nm

Collin, Guy J.; Deslauriers, Hélène; Wiȩckowski, Andrzej

doi:10.1021/j150608a005

Cited by 22 publications

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“…At zero pressure, the @(isoprene) values, measured in the presence of 10% oxygen, are 0.74 and 0.79 in the 23DMB and 33DMB systems, respectively. Since the $(process [2] or [3]) value is less than unity, the majority of A* or B* decomposes at zero pressure. Another compound observed in the presence of oxygen and having a Stern-Volmer behavior is 1,2-butadiene (Fig.…”

Section: At 1849 Nmmentioning

confidence: 99%

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

Deslauriers¹,

Collin²

1985

Can. J. Chem.

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HELENE DESLAURIERS and GUY J. COLLINS. Can. J. Chem. 63, 62 (1985).The photofragmentation of 2,3-dimethylbutene and 3.3-dimethylbutene has been studied at 147 and 184.9 nm in the gas phase. The main primary decomposition process at both wavelengths involves the rupture of a P(C-C) bond. The quantum yield for this process is higher than 0.7 at 147 nm and is probably even higher at 184.9 nm. All dimethallyl radicals formed at 147 nm in this process decompose at low pressure, but some of them isomerize from the a , P -to the a,a-structure (and vice versa) -via a 1.4-H transfer -before decomposition. At 184.9 nm, the same primary process is used to get a rough value for the lifetime of the photoexcited molecule, compared with the one made with RRKM calculations by assuming that all the photon energy resides in the vibrational framework of the fundamental electronic state. These lifetimes are about one nanosecond or less.HELENE DESLAURIERS et GUY J. COLLINS. Can. J. Chem. 63, 62 (1985).On a CtudiC la photolyse des dimkthyl-2.3-et -3,3-butene-l a 147 et a 184,9 nm. Le principal mode de fragmentation de la molCcule photoexcitCe implique la rupture d'un lien C-C situC en position P.. Le rendement quantique de ce processus primaire est supCrieur a 0,7 a 147 nm et peut-Ctre plus ClevC encore a 184,9 nm. A 147 nm, tous les radicaux dimCthallyles se dkcomposent ii basse pression, mais certains le font aprks isomkrisation par transfert interne 1,4 d'un atome d'hydrogkne. A 184,9 nm le mCme processus primaire est utilisC pour determiner le temps de vie de la molCcule photoexcitke. Ce temps de vie, de I'ordre ou moins de la nanoseconde, est cornpark avec celui que I'on peut obtenir 21 I'aide de calculs RRKM en supposant que toute I'Cnergie du photon est distribuCe dans le tissu vibrationnel de la molCcule. IntroductionWe have recently studied the gaseous photolysis of tetramethylethylene and I-hexene at 184.9 nm. At low pressures (1 Tom = 1330 N m-2), both photoexcited molecules decompose. The photoexcited I-hexene molecule gives rise to the rupture of the P(C-C)bond (1) and that of the tetramethylethylene -a molecule without the P(C-C) bondgives rise to the rupture of either a P(C-H) or a a(C-C) bond (2) with similar probability. Moreover, at high pressure (above 100 Torr), isomers are formed with rather high quantum yields in the tetramethylethylene case: @(isomers) = 0.34 in the presence of high propane pressure (3). Conversely, the isomerization processes are very low or not even observed in the I-hexene case: @(isomers) 5 0.01 (1).This work has two main purposes. First, we shall examine in other C6 terminal olefins the validity of the rupture of the P(C-C) bond at low pressure, and, if possible, we shall estimate the lifetime of the photoexcited molecule. Second, we shall try to reconcile the apparent conflict observed above at high pressure: does the photoexcited molecule isomerize? We have chosen 2,3-dimethylbutene (23DMB) and 3,3-dimethylbutene (33DMB) for this study. It is hoped that any structural effect inside the C...

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Section: At 1849 Nmmentioning

confidence: 99%

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

Deslauriers¹,

Collin²

1985

Can. J. Chem.

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“…1): [5] M3B 1 ** -, CH3 .+ C H , C H = C H~H~* ou CH3CHCH=CH2* A H = 69 kcal mol-' (16) [6] C H~~H C H = C H~* ou C H~C H = C H~H , * -+…”

Section: Resultatsmentioning

confidence: 99%

“…Si l'on sait mesurer le pentene-2, il faut aussi tvaluer la fraction de la recombinaison mtthyle + a-methallyle qui reforme le monomere (20). Quant au C,Hl4, produit non analyst, on peut aussi l'estimer via la relation suivante (2 1): L'utilisation de cette tquation de concert avec les remarques prectdentes montre que le rendement de la rtaction [5] I1 faut aussi noter la formation d'isoprene qui pourrait &tre le rtsultat du mtcanisme suivant (Fig. 2):…”

Section: H + Ch2=chch=ch2unclassified

“…(cas du M3B1). Les rendements quantiques de ces deux produits formts dans les rtactions [5]- [7] et [14]- [16] sont susceptible~ de suivre la loi de Stern-Volmer. Par exemple, dans le cas du M2B 1 (Fig.…”

Section: H + Ch2=chch=ch2unclassified

“…A 185 nrn, les trimethyltthylene (rnCthyl-2-butene-2; M2B2) et tttrarntthyltthylene ont rnontrt un cornporternent sirnilaire avec en outre formation d'isornkres (4,5). Le prisent rapport a pour but de vtrifier A 185 nrn la validite du rnicanisrne rtactionnel de fragmentation propose a plus courtes longueurs d'onde.…”

Section: Introductionunclassified

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Photolyse du méthyl-3-butène-1 et du méthyl-2-butène-1 à 185 nm

Houde¹,

Deslauriers²,

Collin³

1983

Can. J. Chem.

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, 962 (1983).Nous avons CtudiC la photolyse du methyl-3-butkne-l (M3B1) et du mCthyl-2-butkne-l (M2B1) i 185 nm cn phase gazeuse. Les processus primaires de fragmentation observes confirment la prCpondCrance de la fragmentation via la rupture de la liaison P(C-C) avec formation concomitante de radicaux mCthyles et soit de radicaux a-mCthallyles (cas du M3B1) soit de radicaux P-mCthallyles (cas du M2B1). La comparaison de ces deux systttmes inspire une mCthode trks primitive quant B la determination de I'Cnergie supportCe par les radicaux mCthallyles: 48% des radicaux C4H7* ainsi produits ont une Cnergie interne entre 42 et 58 kcal mol-' a 185 nm. D'autres comparaisons sont faites avec ce qui a Ct C observC precedemment 163 et a 174 nm. Ces observations confirment la conclusion que I'knergie du photon est trks probablement distribuCe de f q o n statistique dans le tissu vibrationnel de la molCcule photoexcitee avant sa fragmentation. DANIELLE HOUDE, HELENE DESLAURIERS, and GUY J. COLLIN. Can. J. Chem. 61, 962 (1983).The gaseous photolysis of 3-methyl-I-butene (M3B I ) and of 2-methyl-I-butene (M2B I) has been studied at 185 nm. The observed primary fragmentation processes of the photoexcited molecules confirm the leading role of the P(C-C) bond rupture, with formation of methyl radicals and either a-methallyl radicals (M3BI system) or P-methallyl radicals (M2BI system). The comparison of the two systems suggests a very simple method to evaluate the energy content of the methallyl excited radical: 48% of C4H7* radicals so produced have an energy content of 50 ? 8 kcal mol-' at 185 nm. Other comparisons have been made with results previously obtained at 163 and 174 nm. These observations support the idea that the energy of the incident photon is very likely distributed among the vibrational frame of the photoexcited molecule before the occurrence of fragmentation processes.

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185-nm-Photochemie von Olefinen, gespannten Kohlenwasserstoffen und Azoalkanen in Lösung

Adam¹,

Oppenländer²

1986

Angew. Chem.

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Professor Dietrich Schulte-Frohlinde zum 60. Geburtstag gewidmetDie Moglichkeit, Chromophore, die nur im Vakuum-UV absorbieren, bei 185 nm direkt anzuregen, hat im letzten Jahrzehnt zur Belebung dieses Teilgebiets der Photochemie gefuhrt.Wlhrend Reaktionen in der Gasphase bei 1 < 200 nm schon eingehend untersucht worden sind, erbrachte die intensive Erforschung der 185-nm-Photochemie von organischen Verbindungen in Losung neue Erkenntnisse. Trotz hoher Anregungsenergie werden selektive Photoreaktionen aus kurzlebigen Singulett-Zustanden (Rydberg-Photochemie) ausgelost.Anders als bei der konventionellen Photochemie (1 > 220 nm) treten bei 185-nm-Bestrahlung bevorzugt intrarnolekulare Umlagerungen, Spaltungen und Isomerisierungen auf, wtlhrend intermolekulare Radikalkupplungen und -abstraktionen sowie Dimerisierungen (n,n*-Anregung) nur geringfugig konkurrieren. Neben der leicht moglichen Denitrogenierung photoresistenter (,,reluctant") Azoalkane zeichnen sich wichtige Anwendungsgebiete der kurzwelligen Photolyse auch in der Technik (Photolithographie) und der Medizin (193-nmLaser) ab. Die Erweiterung des Synthesepotentials der 185-nm-Photochemie -bisher auf direkte cis/trans-Isornerisierungen beschrankt -, ist eine Herausforderung fur den Chemiker. Warum 185-nm-Photochemie?

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Photolysis of gaseous tetramethylethylene between 185 and 230 nm

Cited by 22 publications

References 0 publications

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

Photolyse du méthyl-3-butène-1 et du méthyl-2-butène-1 à 185 nm

185-nm-Photochemie von Olefinen, gespannten Kohlenwasserstoffen und Azoalkanen in Lösung

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