Synthesis and <sup>1</sup>H and <sup>13</sup>C nuclear magnetic resonance spectra of some 4-alkylidene-1-pyrazolines and alkylidenecyclopropanes

Crawford, Robert J.; Tokunaga, Hirokazu; Schrijver, L. M. H. C.; Godard, Jacky C.; Nakashima, Thomas T.

doi:10.1139/v78-166

Cited by 25 publications

(11 citation statements)

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“…The CH2 proton shift in the methylenecyclopropane ring is 1.0 ppm, and the l3C shift is 2.8 ppm. 18 The CH2 stretching frequencies in C1CB are well below 3000 cm '1 and are in good agreement with those for CB. In contrast, corresponding CH2 stretching frequencies in methylenecyclopropane are mostly well above 3000 cm"1.…”

Section: Resultssupporting

confidence: 69%

“…1 -Chloro-1 -fluorocyclobutane had an elution time of 2.4 relative to fluorocyclobutane. For 1-chloro-1-fluorocyclobutane, the gas-phase infrared spectrum showed bands (cm-1) at 3020 s, 2970 s, 1425 m, 1270 s, 1225 m, 1165 ppm (d (JCF = 4.5 Hz)) for =CH, and 32.8 (d (JCF = 20.5 Hz)), 18.2 ppm (d (yCF = 24.3 Hz)) for CH2's; and the l9F NMR spectrum, a signal at -81.9 ppm (t (7HF = 14.6 Hz) of d (JHF = 8.7 Hz) of t (/hf = 6.4 Hz)).…”

Section: Methodsmentioning

confidence: 99%

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Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Craig¹,

Borick²,

Tucker³

et al. 1991

J. Phys. Chem.

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3549Mass spectroscopic Knudsen cell studies of the vapor over P4OI0(H) at 150, 315, and 400 OC have shown that P4OIo undergoes a phase transition which lowers the vapor pressure at 300 OC and that the vapor is composed of P4O10, P409, and P408 molecules with an approximate ratio of 10:3:1; furthermore, the decomposition products P408 and P407 showed increased concentration with higher Knudsen cell temperat~res.'~ While species such as P30e7' were produced by 40-eV electron impact, they showed no temperature dependence and were unique to mass spectroscopic studies. The P202-s+ ions were also produced by the electron impact process, as indicated by their high appearance potentials, but they showed increased intensities a t higher temperatures, corroborating the present matrix infrared observation that P40s and P407 are more prone to unimolecular cage decomposition than P4Olo. ConclusionsThe YAG laser evaporation of hexagonal (molecular) P4Olo produced mainly P4OIo with small yields of the P20s and POz decomposition products. The depolymerization of orthorhombic (covalent network) P4O10 with laser ablation gave a randomized distribution of PO, PO2, P20, P204, and P20s fragmentation (19) (a) Muenow, D. W.; Uy, 0. M.; Margrave, J. L. J. Inorg. Nucl. Chem. 1970, 32, 3459. (b) Hashizume, A.; Wasada, N.; Tsuchiya, T. Bull. Chem. SOC. Jpn. 1966,39, 150.products, where the smaller fragments had high intensities, and little P4O10. The HOP0 and HOP02 molecules were observed as hydrolysis intermediates. Thermolysis of P4Olo at 900-950 "C produced a nonrandomized distribution of depolymerization products, which favored P409 and PO2, and to a lesser extent P4O8. P205, and P2O4.Reactive laser ablation of red phosphorus and oxygen produced the same species as the depolymerization reactions of orthorhombic P4010 and earlier reactions of P2 with O2 and 03.57 The reaction was confined to the plume produced by the laser owing to the production of excited phosphorus fragment species. This work shows that POz is a particularly stable gaseous species20 and suggests that molecular P205 can also be observed in the gas phase.Laser ablation has been used for a number of years with great success in combination with matrix-isolation fluorescence spectroscopy by Bondybey and co-workers2I and for matrix-isolation ESR studies by Knight." This work exploits the combination of laser ablation of polymerized substrates and reactive laser ablation with matrix infrared spectroscopy. (20) Kawaguchi, K.; Saito, S.; Hirota, E.; Ohashi, N.Gas-phase infrared spectra and liquid-phase Raman spectra are presented for 1 -chlorocyclobutene and 1 -fluorocyclobutene. Complete assignments of vibrational fundamentals are proposed for these molecules of C, symmetry. For 1 -chlorocyclobutene (cm-I): (a') . Frequencies of CH-rich modes correlate closely for these isotopomer-like molecules. These results along with a Raman spectrum of liquid cyclobutene near -100 OC have provided evidence for assigning five unsettled vibrational fundamentals of cyclobutene. These modes...

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Section: Resultssupporting

confidence: 69%

Section: Methodsmentioning

confidence: 99%

Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Craig¹,

Borick²,

Tucker³

et al. 1991

J. Phys. Chem.

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“…3-Methyl-4-methylenepyrazolldine-5,5-d2 Hydrochloride (31). A solution of potassium hydroxide (1.5 g) in 15 mL of «-propanol, 1.5 mL of water, and 30 (0.9 g, 4 mmol) was maintained at 100 ®C for 3 h under an inert atmosphere.…”

Section: Methodsmentioning

confidence: 99%

“…3-Methyl-4-methylenepyrazoliiie-5,5-</2 (11). The hydrochloride 31 (0.45 g, 3 mmol) dissolved in 2 mL of methanol was added slowly to a slurry of red mercuric oxide (3.4 g) and sodium sulfate 3.4 g) in 100 mL of ether. After 0.5 h of stirring, the solids were filtered off and washed with ether, and the organic layer was concentrated.…”

Section: Methodsmentioning

confidence: 99%

Intramolecular steric factors in the thermolysis of 4-alkylidene-1-pyrazolines

LeFevre¹,

Crawford²

1986

J. Am. Chem. Soc.

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“…The methylenepyrazoline 1 as well as its photoproducts, i. e. the alkylidenecyclopropanes 4 and 5, are characterized by high-field proton (Table 2) and carbon-13 spectra ( 17,20). Moreover, it has now been possible to resolve all of the expected longe-range couplings in the proton spectrum of the isopropylidenecyclopropane 5, i.e.…”

mentioning

confidence: 99%

Photoreduction on Irradiation of 3,3,5,5‐Tetramethyl‐4‐methylene‐1‐pyrazoline. — An Overlooked Example of a Reaction Competing with the Extrusion of Molecular Nitrogen from Reluctant Azoalkanes

Quast

Jakobi

1991

Chem. Ber.

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J 1H-Pyrazole, 2,3,4,5-tetrahydro-3,3,5,5-tetramethyl-4-methylene-/ Photolysis / Photoreduction / Extrusion of molecular nitrogenThe photolysis of the 4-methylene-1-pyrazoline 1 is reinvestigated under a variety of experimental conditions. Direct irradiation (350-nm light) affords the alkylidenecyclopropanes 4 and 5 as predominant products, besides molecular nitrogen, and in a constant ratio of (55 * 1): (45 T l), which is not altered in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) or piperylene nor in [D,]acetone solution. When oxygen is excluded, an additional compound is formed whose proportion depends on the capability of the solvent to act as hydrogen donor. In the presence of three equivalents of DABCO, it eventually becomes the major product. The 4-methylenepyrazolidine structure 13 of the novel photoproduct is established by NMR spectroscopy, a comparison with an authentic sample, obtained in quantitative yield by zinc reduction of 1, and reoxidation to 1 as well. An extensive investigation to detect any traces of the 4-isopropylidene-2-pyrazoline 6 in the irradiated solutions has failed. This result is at variance with recent disclosures reporting evidence for a turnaround photoisomerization of 1 via diazenylallyl diradicals. The contribution of photoreduction to the decay of the first excited singlet state of reluctant azo compounds is emphasized.Numerous investigations have been concerned with the mechanism and applications of the photoextrusion of molecular nitrogen from 4-alkylidene-l-pyra~olines~~~). Irradiation of such azo compounds represents a convenient route to alkylidenecyclopropanes and to matrix-isolated trimethylenemethanes as well4), which have been invoked as intermediates in solution and gas-phase photolysis. Following the pioneering work of Andrews and Day5), Bushby and coworkers6' have studied the regioselectivity of alkylidenecyclopropane formation in the direct photolysis of 4-alkylidene-3,3,5,5-tetramethyl-l-pyrazolines, i.e. the ratio of the least-motion products vs. the thermodynamically favoured non-least-motion products'', e.g. 1 --f 4, 56,R). The observed increase in regioselectivity with the number and bulkiness of substituents at the double bond has been rationalized by simple working hypotheses among other possible more elaborate ones. The favoured explanation involved the initial formation of bis-orthogonal trimethylenemethanes, e. g. 2, which may cyclize to the least-motion product, e.g. 4, or equilibrate to a greater or lesser extent -depending on the bulkiness of the substituents -with mono-orthogonal trimethylenemethanes, e. g. 3, assumed as precursors for both isomeric alkylidenecyclopropanes, viz. 4 and 56). In fact, this hypothesis could be supported later by estimates of the influence of methyl substituents on trimethylenemethane diradicals in the planar and mono-orthogonal geometriesg1.More recently, Adam and Dorr have detected traces (ca. 0.5%) of a third product in the direct photolysis of 1 in pentane solution. The trace component is identified as the 2...

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Synthesis and ¹H and ¹³C nuclear magnetic resonance spectra of some 4-alkylidene-1-pyrazolines and alkylidenecyclopropanes

Cited by 25 publications

References 2 publications

Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Intramolecular steric factors in the thermolysis of 4-alkylidene-1-pyrazolines

Photoreduction on Irradiation of 3,3,5,5‐Tetramethyl‐4‐methylene‐1‐pyrazoline. — An Overlooked Example of a Reaction Competing with the Extrusion of Molecular Nitrogen from Reluctant Azoalkanes

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Synthesis and 1H and 13C nuclear magnetic resonance spectra of some 4-alkylidene-1-pyrazolines and alkylidenecyclopropanes

Cited by 25 publications

References 2 publications

Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Vibrational spectra and assignments for 1-fluoro- and 1-chlorocyclobutenes: revised assignment for cyclobutene

Intramolecular steric factors in the thermolysis of 4-alkylidene-1-pyrazolines

Photoreduction on Irradiation of 3,3,5,5‐Tetramethyl‐4‐methylene‐1‐pyrazoline. — An Overlooked Example of a Reaction Competing with the Extrusion of Molecular Nitrogen from Reluctant Azoalkanes

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Synthesis and ¹H and ¹³C nuclear magnetic resonance spectra of some 4-alkylidene-1-pyrazolines and alkylidenecyclopropanes