Substituent chemical shifts in NMR. 1—Proton resonance spectra and geometries of norbornene, norbornane and adamantane

Abraham, Raymond J.; Fisher, Julie

doi:10.1002/mrc.1260231014

Cited by 49 publications

(26 citation statements)

References 17 publications

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“…As the experimental bond lengths mechanistic organic as well as to structural chemists probing, contained in rep0rts differed from those we both experimentally and theoretically, the relationship between calculated by ab initio means, additional structural information electronic structure and spectroscopic properties (1)(2)(3)(4)(5). As a from spectra seemed continuation of related studies in our separate laboratories, we have investigated the microwave and far-infrared spectra of 8 -0xabicyc10 [3.2.1] octane, and compared the experimental geometry to that calculated by ab initio means at the STO-3G and 3-21G levels.…”

Section: Introductionmentioning

confidence: 69%

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

Eggimann¹,

Smithson²,

Wieser³

et al. 1990

Can. J. Chem.

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. Can. J. Chem. 68, 267 (1990). The structure of 8-oxabicyclo[3.2.l]octane was calculated by a b initio means at the STO-3G level, and the structural data used to assign the microwave spectrum of the title compound in the range of 26.5 to 40 GHz fitting 144 lines up to J = 48 by adjusting the rotational and three centrifugal distortion constants in the Watson A reduction. Structural parameters were deduced from the rotational constants by allowing all bond lengths and angles to vary in a least-squares manner. These parameters were in good agreement with those calculated at the STO-3G and 3-21G levels. Of many satellite lines observed, only the most intense could be utilized for locating the two lowest fundamental vibrations, estimated to occur at 190 and 240 cm-'. The far-infrared spectrum is reported in the region of 80 to 300 cm-I, exhibiting only one distinct sequence of Q branches at 264 cm-I. On the basis of unscaled a b initio force fields at both levels of the theory the corresponding fundamentals are assigned, respectively, to a twisting (A") and a bending (A') of the cycloheptane ring.

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Section: Introductionmentioning

confidence: 69%

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

Eggimann¹,

Smithson²,

Wieser³

et al. 1990

Can. J. Chem.

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“…[71] The potential for long-range W-couplings in diamondoids was recognized early [20] and applied with COSY data to assigning the 1 H NMR spectra of adamantanes. [72,73] W-couplings present in COSY data of [123]-tetramantane and [1(2)3]-tetramantane are crucial to their NMR spectral assignment processes. The value of 4 J HH long-range coupling for higher diamondoids NMR analyses warrants application of techniques targeting smaller long-range couplings.…”

Section: Discussionmentioning

confidence: 99%

NMR spectral properties of the tetramantanes – nanometer‐sized diamondoids

Balaban

Young

Plavec

et al. 2015

Magnetic Reson in Chemistry

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Tetramantanes, and all diamondoid hydrocarbons, possess carbon frameworks that are superimposable upon the cubic diamond lattice. This characteristic is invaluable in assigning their (1)H and (13)C NMR spectra because it translates into repeating structural features, such as diamond-cage isobutyl moieties with distinctively complex methine to methylene signatures in COSY and HMBC data, connected to variable, but systematic linkages of methine and quaternary carbons. In all tetramantane C22H28 isomers, diamond-lattice structures result in long-range (4)JHH, W-coupling in COSY data, except where negated by symmetry; there are two highly symmetrical and one chiral tetramantane (showing seven (4)JHH). Isobutyl-cage methines of lower diamondoids and tetramantanes are the most shielded resonances in their (13)C spectra (<29.5 ppm). The isobutyl methylenes are bonded to additional methines and at least one quaternary carbon in the tetramantanes. W-couplings between these methines and methylenes clarify spin-network interconnections and detailed surface hydrogen stereochemistry. Vicinal couplings of the isobutyl methylenes reveal positions of the quaternary carbons: HMBC data then tie the more remote spin systems together. Diamondoid (13) C NMR chemical shifts are largely determined by α and β effects, however γ-shielding effects are important in [123]tetramantane. (1)H NMR chemical shifts generally correlate with numbers of 1,3-diaxial H-H interactions. Tight van der Waals contacts within [123]tetramantane's molecular groove, however, form improper hydrogen bonds, deshielding hydrogen nuclei inside the groove, while shielding those outside, indicated by Δδ of 1.47 ppm for geminal hydrogens bonded to C-3,21. These findings should be valuable in future NMR studies of diamondoids/nanodiamonds of increasing size.

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“…Equation (8) provides a much better description of propanic coupling than others which have been proposed. 15,18,53 For example, the correlation with just the first term Acos 2 ϕ 1 cos 2 ϕ 3 is much worse (SD D 0.42 Hz r 2 D 0.142) but would not be quite this bad since the coefficient A was assigned different values depending on the range of dihedral angles. 15 The inclusion of additional trigonometric terms in Eqn(8) was investigated and gives some improvement.…”

Section: Structural Dependence Of Propanic H -C -C -C -H Coupling 4 Jmentioning

confidence: 96%

“…This is not surprising in view of the spectral complexity for 8-12-spin systems even at high magnetic fields. 18 In a few cases average values of coupling constants derived from substituted molecules have been reported. 19 -25 Additionally, some values have been based on deuterium substitution and/or coupled 13 C spectra.…”

Section: A Dft/fpt Investigation Of Long-range Coupling 4 J(hh ) In mentioning

confidence: 99%

DFT/FPT studies of the structural dependencies of long‐range ¹H,¹H coupling over four bonds ⁴J(H,H′) in propanic and allylic systems

Barfield

2003

Magnetic Reson in Chemistry

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A study is presented of the structural dependencies for scalar J-coupling across four bonds in propanic and allylic systems. Density functional theory (DFT) and finite perturbation theory (FPT) were used to obtain the Fermi contact (FC) contributions to 1 H, 1 H coupling. Interproton couplings 4 J(H,H ) in propane were obtained as functions of the dihedral angles j 1 and j 3 , which are measured about the C(1) -C(2) and C(2) -C(3) bonds, respectively, and on the C(1) -C(2) -C(3) internal angle q 2 . A four-term trigonometric expression reproduces the dependence on j 1 and j 3 with a standard deviation of 0.1 Hz. The molecular structures for a series of bicycloalkanes were fully optimized and DFT/FPT results for 4 J(H,H ) are in good agreement with the available experimental data. However, in non-W arrangements of bicyclic systems the propane trigonometric expression for 4 J(H,H ) often gives signs opposite to those observed. It is now clear the conformational dependence of coupling constants in propane is not, in general, applicable to bicyclic systems. The DFT/FPT propane-based results for coupling involving a methyl group (H -C -C -CH 3 ) are in better conformity with the experimental data. The DFT/FPT results for cisoid and transoid allylic coupling 4 J(H,H ) in propene were obtained as functions of the dihedral angle j measured about the C(2) -C(3) bond. Trigonometric expressions with three terms reproduce the calculatedpropene results with standard deviations 0.1 Hz. The molecular structures for a series of bicycloalkenes were fully optimized and DFT/FPT results for cisoid and transoid coupling are in fairly good agreement with the available experimental data. In contrast to the propanic coupling, the trigonometric expressions for propenic coupling constants are generally applicable to conformational analyses in bicycloalkenes.

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Substituent chemical shifts in NMR. 1—Proton resonance spectra and geometries of norbornene, norbornane and adamantane

Cited by 49 publications

References 17 publications

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

NMR spectral properties of the tetramantanes – nanometer‐sized diamondoids

DFT/FPT studies of the structural dependencies of long‐range ¹H,¹H coupling over four bonds ⁴J(H,H′) in propanic and allylic systems

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Substituent chemical shifts in NMR. 1—Proton resonance spectra and geometries of norbornene, norbornane and adamantane

Cited by 49 publications

References 17 publications

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

NMR spectral properties of the tetramantanes – nanometer‐sized diamondoids

DFT/FPT studies of the structural dependencies of long‐range 1H,1H coupling over four bonds 4J(H,H′) in propanic and allylic systems

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DFT/FPT studies of the structural dependencies of long‐range ¹H,¹H coupling over four bonds ⁴J(H,H′) in propanic and allylic systems