Experimental and quantum chemical investigation of the stereochemical dependence of spin coupling constants in symmetrical strained alkenes

Berger, Stefan; Krebs, Adolf; Thlke, Bernd; Siehl, Hans‐Ullrich

doi:10.1002/1097-458x(200007)38:7<566::aid-mrc674>3.0.co;2-h

Cited by 6 publications

(1 citation statement)

References 19 publications

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“…Bertozzi reported that triazole regioisomers (1,5 and 1,4) are formed in a nearly equivalent ratio , (consistent with our findings above). A similar lack of regioselective preference has also been reported for mesitonitrile cycloadditions to methoxy substituted cyclooctenes . To further investigate the substituent effects, we have computed the activation barriers for benzyl azide with mono- and disubstituted cyclooctynes, using SCS-MP2/6-31G(d)//B3LYP/6-31G(d) that was shown above to reproduce the fluorine effect well and also showed essentially no energy difference between the boat and chair transition states.…”

Section: Resultssupporting

confidence: 55%

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

et al. 2009

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The transition states and activation barriers of the 1,3-dipolar cycloadditions of azides with cycloalkynes and cycloalkenes were explored using B3LYP density functional theory (DFT) and spin component scaled SCS-MP2 methods. A survey of benzyl azide cycloadditions to substituted cyclooctynes (OMe, Cl, F, CN) showed that fluorine substitution has the most dramatic effect on reactivity. Azide cycloadditions to 3-substituted cyclooctynes prefer 1,5-addition regiochemistry in the gas phase, but CPCM solvation abolishes the regioselectivity preference, in accord with experiments in solution. The activation energies for phenyl azide addition to cycloalkynes decrease considerably as the ring size is decreased (cyclononyne DeltaG(double dagger) = 29.2 kcal/mol, cyclohexyne DeltaG(double dagger) = 14.1 kcal/mol). The origin of this trend is explained by the distortion/interaction model. Cycloalkynes are predicted to be significantly more reactive dipolarophiles than cycloalkenes. The activation barriers for the cycloadditions of phenyl azide and picryl azide (2,4,6-trinitrophenyl azide) to five- through nine-membered cycloalkenes were also studied and compared to experiment. Picryl azide has considerably lower activation barriers than phenyl azide. Dissection of the transition state energies into distortion and interaction energies revealed that "strain-promoted" cycloalkyne and cycloalkene cycloaddition transition states must still pay an energetic penalty to achieve their transition state geometries, and the differences in reactivity are more closely related to differences in distortion energies than the amount of strain released in the product. Trans-cycloalkene dipolarophiles have much lower barriers than cis-cycloalkenes.

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Section: Resultssupporting

confidence: 55%

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

et al. 2009

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Applications of cryogenic NMR probe technology to long‐range ¹H‐¹⁵N 2D NMR studies at natural abundance

Crouch

Llanos

Mehr

et al. 2001

Magnetic Reson in Chemistry

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The development of new NMR probe technologies has been an active area of research effort for the past decade. Recently, cryogenically cooled NMR probes have been the subject of considerable interest in the light of the large gains in sensitivity and hence savings in spectrometer time that can be realized by utilizing this technology. With low gamma nuclides, such as 15 N, time savings may be less of an issue than the ability to work with available samples rather than having to isolate additional material for analysis. Results of 5-10 Hz optimized CIGAR-HMBC 1 H-15 N experiments at natural abundance obtained using a 5 mm Varian 1 H-15 N Cryo-Q NMR probe are compared with those from a 3 mm gradient inverse triple resonance probe using a 2 mg sample of the oxazolidinone antibiotic eperezolid in a 3 mm NMR tube. Using the cryogenic NMR probe, a 1 H-15 N CIGAR-HMBC spectrum in which most previously reported long-range couplings are observed was recorded in ∼10 min; almost all of the expected long-range responses were observed within 26 min. Acquiring the same data set with identical parameters using a conventional 3 mm gradient inverse triple resonance probe gave data that were of substantially lower quality. Acquiring data comparable to the 26 min cryogenic probe data with the conventional 3 mm probe required ∼4 h to observe all of the responses and ∼18 h to obtain a spectrum with a signal-to-noise ratio comparable to the data set acquired with the cryogenic NMR probe. Copyright Since long-range heteronuclear shift correlation experiments are generally considered to be about a factor of four less sensitive than the corresponding direct correlation experiments, considerable efforts have been directed toward the enhancement of NMR sensitivity to facilitate the acquisition of these data.15 N, being an inherently insensitive nuclide, places still more stringent demands on spectrometer

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Application of 13C–13C Spin–Spin Couplings in Structural Studies on Organic Compounds

Kamieńska‐Trela¹,

Wójcik²

2013

Science and Technology of Atomic, Molecular, Condensed Matter &Amp; Biological Systems

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Experimental and quantum chemical investigation of the stereochemical dependence of spin coupling constants in symmetrical strained alkenes

Cited by 6 publications

References 19 publications

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

Applications of cryogenic NMR probe technology to long‐range ¹H‐¹⁵N 2D NMR studies at natural abundance

Application of 13C–13C Spin–Spin Couplings in Structural Studies on Organic Compounds

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Experimental and quantum chemical investigation of the stereochemical dependence of spin coupling constants in symmetrical strained alkenes

Cited by 6 publications

References 19 publications

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

Reactivity and Regioselectivity in 1,3-Dipolar Cycloadditions of Azides to Strained Alkynes and Alkenes: A Computational Study

Applications of cryogenic NMR probe technology to long‐range 1H‐15N 2D NMR studies at natural abundance

Application of 13C–13C Spin–Spin Couplings in Structural Studies on Organic Compounds

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Applications of cryogenic NMR probe technology to long‐range ¹H‐¹⁵N 2D NMR studies at natural abundance