- The disappearance of aryl carbenes in a reactive matrix
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The disappearance of diphenylmethylene, fluorenylidene and phenylmethylene in isobutylene and fluorolube was monitored by esr spectroscopy at temperatures between 77°K and 171°K.
- Lin, Cheng-Tung,Gaspar, Peter P.
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Read Online
- Nitrile imines: Matrix isolation, IR spectra, structures, and rearrangement to carbodiimides
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The structures and reactivities of nitrile imines are subjects of continuing debate. Several nitrile imines were generated photochemically or thermally and investigated by IR spectroscopy in Ar matrices at cryogenic temperatures (Ph-CNN-H 6, Ph-CNN-CH317, Ph-CNN-SiMe323, Ph-CNN-Ph 29, Ph3C-CNN-CPh334, and the boryl-CNN-boryl derivative 39). The effect of substituents on the structures and IR absorptions of nitrile imines was investigated computationally at the B3LYP/6-31G level. IR spectra were analyzed in terms of calculated anharmonic vibrational spectra and were generally in very good agreement with the calculated spectra. Infrared spectra were found to reflect the structures of nitrile imines accurately. Nitrile imines with IR absorptions above 2200 cm -1 have essentially propargylic structures, possessing a CN triple bond (typically PhCNNSiMe323, PhCNNPh 29, and boryl-CNN-boryl 39). Nitrile imines with IR absorptions below ca. 2200 cm-1 are more likely to be allenic (e.g., HCNNH 1, PhCNNH 6, HCNNPh 43, PhCNNCH317, and Ph3C-CNN-CPh334). All nitrile imines isomerize to the corresponding carbodiimides both thermally and photochemically. Monosubstituted carbodiimides isomerize thermally to the corresponding cyanamides (e.g., Ph-N=C=N-H 5 Ph-NH-CN 8), which are therefore the thermal end products for nitrile imines of the types RCNNH and HCNNR. This tautomerization is reversible under flash vacuum thermolysis conditions.
- Begue, Didier,Qiao, Greg Guanghua,Wentrup, Curt
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p. 5339 - 5350
(2012/05/20)
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- Evidence of hydrogen migration in an alkylphenyldiazirine excited state
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(Figure Presented) Ultrafast photolysis (350 nm) of alkylphenyldiazirines promotes the diazirine to the S1 excited state. Solvent and substituent effects on the excited state lifetimes indicate that the S 1 state is highly polarized and undergoes a [1,2]-H shift in concert with nitrogen extrusion in cyclohexane.
- Zhang, Yunlong,Kubicki, Jacek,Platz, Matthew S.
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supporting information; experimental part
p. 3182 - 3184
(2010/09/16)
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- Direct observation of carbene and diazo formation from aryldiazirines by ultrafast infrared spectroscopy
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Ultrafast laser flash photolysis (λex = 270 nm) of phenyldiazirine produces transient infrared absorptions at 2040 and 1582 cm-1. The first band is assigned to phenyldiazomethane, and the second is assigned to singlet phenylcarbene. This assignment is consistent with DFT calculations. Diazo band integration reveals that photoisomerization from diazirine to diazo occurs within a few picoseconds of the laser pulse. The majority of carbene produced is also formed instantaneously. Copyright
- Zhang, Yunlong,Burdzinski, Gotard,Kubicki, Jacek,Platz, Matthew S.
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supporting information; experimental part
p. 16134 - 16135
(2009/05/09)
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- Cycloaddition of Bu(n)3P·CS2: Direct one-pot conversion of strained double bonds to 2-alkylidene-1,3-dithiolanes
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Reaction of the adduct between tri-n-butylphosphine and carbon disulfide 1 with norbornene gives the novel zwitterionic structure 9. In solution this dissociates to the ylide 8 which undergoes Wittig reaction with aldehydes. Using the same method, the overall conversion of the strained double bond in a variety of bicyclo[2.2.1]alkenes into 2-benzylidene-1,3-dithioles 15-24 has been achieved and the reaction is also applicable to norbonnadiene, affording bis-dithiolanes 29-31.
- Aitken, R. Alan,Carcas, Katriona,Hill, Lawrence,Massil, Tracy,Raut, Swati V.
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p. 2261 - 2270
(2007/10/03)
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- 1,2,4,6-CYCLOHEPTATETRAENE: THE KEY INTERMEDIATE IN ARYLCARBENE INTERCONVERSIONS AND RELATED C7H6 REARRANGEMENTS
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Thermolysis or photolysis of phenyldiazomethane (2) produces phenylmethylene (3), which ring-expands to give 1,2,4,6-cycloheptatetraene (6).Spectroscopic and chemical evidence rule out bicyclo(4.1.0)hepta-2,4,6-triene (4), cycloheptatrienylidene (5), and bicyclo(3.2.0)hepta-1,3,6-triene (11) intermediates.The strained allene in cycloheptatetraene (6) exhibits infrared absorption at 1824 and 1816 cm-1.Deuterium substitution produces the expected 10-cm-1 shift in the allene absorption.Fluorine or chlorine substitution substantially enhances the allene absorption intensity.Deuterium labeling studies reveal that the intramolecular chemistry of cycloheptatetraene (6) involves reversible thermal or photochemical equilibriation with phenylmethylene (3).The intermolecular chemistry of 6 involves dimerization.At temperatures as low as 10 K, 6 forms a labile (2+2) dimer,7, which undergoes thermally allowed, electrocyclic ring opening to give heptafulvalene (8) upon warming to room temperature.The rearrangements of 7-acetoxynorbornadiene (9), 2-diazobicyclo(3.2.0)hepta-3,6-diene (31), and 8-diazobicyclo(2.2.2)octa-2,5-dien-7-one (33) all involve cycloheptatetraene (6) intermediates.
- McMahon, Robert J.,Abelt, Christopher J.,Chapman, Orville L.,Johnson, Jeffery W.,Kreil, Curits L.,et al.
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p. 2456 - 2469
(2007/10/02)
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