Proton chemical shifts in NMR. Part 16.1 Proton chemical shifts in acetylenes and the anisotropic and steric effects of the acetylene group

Abraham, Raymond J.; Reid, M. M.

doi:10.1039/b009321l

Cited by 15 publications

(12 citation statements)

References 24 publications

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“…On the other hand, the chemical shifts of proton 2 and proton 3 showed little changes. Similar changes were also observed for model compounds (Supporting Information, Scheme S2) . Hence we propose that M3‐isomer 1 is obtained based on the NMR spectrum of the molecule.…”

Section: Resultssupporting

confidence: 82%

Synthesis, characterization, and structure-property investigation of conformationally rigid regioisomers of poly(p-phenylene ethynylene)s

Sen

Valiyaveettil

2016

J. Polym. Sci. Part A: Polym. Chem.

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A series of rigid poly(p‐phenylene ethynylene)s (PPE1–PPE4) with biphenyl‐ (M1–M3) and phenyl‐ (M4) side groups is prepared from appropriately functionalized monomers. Herein, the solution and solid state absorption studies show the polymers have adopted twisted and rigid conformations, as supported by deep HOMO energy levels (−5.76 to −5.81 eV). The absorption maxima of PPE1–PPE3 are shifted to shorter wavelength (λmax = 375–381 nm) as compared to linear poly(p‐phenylene ethynylene)s (446 nm), implying a nonplanar conformation. The self‐assembly of polymers into fibers is examined using scanning electron microscopy. The fibers are not observed in PPE4 with short phenyl side group, suggesting the important role of the interplay between rigidity, position, and size of the side chains toward the formation of fibers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3652–3662

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Section: Resultssupporting

confidence: 82%

Synthesis, characterization, and structure-property investigation of conformationally rigid regioisomers of poly(p-phenylene ethynylene)s

Sen

Valiyaveettil

2016

J. Polym. Sci. Part A: Polym. Chem.

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“…As the theory has been given previously, 1,15 only a brief summary of the latest version (CHARGE7) will be given here. The theory distinguishes between substituent effects over one, two and three bonds, which are attributed to the electronic effects of the substituents and longer range effects due to the electric fields, steric effects and anisotropy of the substituents.…”

Section: Theorymentioning

confidence: 99%

Proton chemical shifts in NMR: Part 17. Chemical shifts in alkenes and anisotropic and steric effects of the double bond

Abraham¹,

Canton²,

Griffiths³

2001

Magnetic Reson in Chemistry

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The 1 H NMR spectra of a number of alkenes of known geometry were recorded in CDCl 3 solution and assigned, namely ethylene, propene, 4-methylcyclohexene, 1,4-dimethylcyclohexene, methylene cyclohexane (in CFCl 3 -CD 2 Cl 2 at 153 K), 5-methylene-2-norbornene, camphene, bicyclopentadiene, styrene and 9-vinylanthracene. These results together with literature data for other alkenes, i.e. 1,3-and 1,4-cyclohexadiene, norbornene, norbornadiene, bicyclo[2.2.2]oct-2-ene and a-and b-pinene, and other data allowed the determination of the olefinic shielding in these molecules. The shielding was analysed in terms of the magnetic anisotropy and steric effects of the double bond together with a model (CHARGE7) for the calculation of the two-and three-bond electronic effects. For the aromatic alkenes ring current and p-electron effects were included. This analysis showed that the double bond shielding arises from both anisotropic and steric effects. The anisotropy is due to the perpendicular term only with a value of 1c.C C/ of −12.1 × 10 −6 cm 3 mol −1 . There is also a steric deshielding term of 82.5/r 6 (r inÅ). The shielding along the p-axis changes sign from shielding at long range (>2.5Å) to deshielding at short range (<2Å). The model gives the first comprehensive calculation of the shielding of the alkene group. For the data set considered (172 proton chemical shifts) ranging from d = 0.48 to 8.39, the r.m.s. error of observed vs calculated shifts was 0.11 ppm.

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“…Thephotoinduced release of C 2 H 2 from 3 results in the formation of the higher symmetric species 4.In 2 successful activation of C 2 H 2 is evidenced by two broad singlets for the acetylenic protons.O xidation to 3 results in as ignificant upfield shift of the signals from d = 12.22 ppm and 11.57 ppm to approximately 10.5 ppm, indicating adrastic increase in acidity compared to free C 2 H 2 which resonates at 1.96 ppm. [14] This is an important finding as deprotonation and nucleophilic attack are discussed as key steps in the mechanistic debate.T he assignment of the C 2 H 2 signals could be confirmed by HSQC cross peaks and by 183 W- 13 Ccoupling in the 13 CNMR spectra (Table 1). Time-resolved 1 HNMR spectra of pure 3 in CD 2 Cl 2 were recorded to follow the photoinduced release of C 2 H 2 from 3 and its reactivation by 4 ( Figure 1).…”

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confidence: 99%

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

2015

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The synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S-Phoz (2-(4',4'-dimethyloxazolin-2'-yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W-acetylene adducts. The featured complexes [W(C2 H2 )(CO)(S-Phoz)2 ] (2) and [WO(C2 H2 )(S-Phoz)2 ] (3) are extremely rare from a synthetic and structural point of view as very little is known about W-C2 H2 adducts. Upon exposure to visible light, 3 can release C2 H2 from its coordination sphere to yield the 14-electron species [WO(S-Phoz)2 ] (4). Under light-exclusion 4 re-activates C2 H2 making this the first fully characterized system for the reversible activation of acetylene.

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Proton chemical shifts in NMR. Part 16.1 Proton chemical shifts in acetylenes and the anisotropic and steric effects of the acetylene group

Cited by 15 publications

References 24 publications

Synthesis, characterization, and structure-property investigation of conformationally rigid regioisomers of poly(p-phenylene ethynylene)s

Synthesis, characterization, and structure-property investigation of conformationally rigid regioisomers of poly(p-phenylene ethynylene)s

Proton chemical shifts in NMR: Part 17. Chemical shifts in alkenes and anisotropic and steric effects of the double bond

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

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