The NMR spectra and conformations of cyclic compoundsV: Proton couplings and chemical shifts in bridged cyclobutanes

Abraham, Raymond J.; Cooper, M. Ashley; Salmon, J. R.; Whittaker, D.

doi:10.1002/mrc.1270040409

Cited by 39 publications

(18 citation statements)

References 36 publications

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“…1 H-and 13 C-NMR: identical with those reported in [28] and [29], resp. This reaction gave ( (9)); 1.93 (dddq, J(5e,5a) = 17.5, J(5e,4) = 5, J(5e,6a) = 5, J(5e,10) = 1.5, H e ÀC(5)); 2.16 (dddqd, J = 17.5, J(5a,6a) = 11, J(5a,4) = 2.5, J(5a,10) = 2.5, J(5a,2) = 1, H a ÀC(5)); 2.35 (br.…”

Section: C-nmrsupporting

confidence: 74%

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Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

Ильина

Волчо

Корчагина

et al. 2007

Helvetica Chimica Acta

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The reactivity of allyl alcohols of the pinane series and of their epoxides in the presence of montmorillonite clay in intra-and intermolecular reactions was studied. Mutual transformations of (+)-trans-pinocarveol ((+)-2) and (À)-myrtenol ((À)-3a) were major reactions of these compounds on askanite-bentonite clay (Schemes 1 and 2). However, the two reactions gave different isomerization products, indicating that the reactivity of the starting alcohol (+)-2 or (À)-3a was different from that of the same compound (+)-2 or (À)-3 formed in the course of the reactions. (À)-cis-and (+)-trans-Verbenol ((À)-16 and (+)-12, resp.), as well as (À)-cis-verbenol epoxide ((À)-20) reacted with both aliphatic and aromatic aldehydes on askanite-bentonite clay giving various heterocyclic compounds (Schemes 4, 5 and 7); the reaction path depended on the structure of both the terpenoid and the aldehyde.

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Section: C-nmrsupporting

confidence: 74%

“…H 2 O soln. in the presence of 6N NaOH according to [28] (9)); 1.27 (s, Me (8)); 1.64 (d, J(7,7') = 10, HÀC (7)); 1.70 -1.76 (m, HÀC (5) [25].…”

Section: C-nmrmentioning

confidence: 99%

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

Ильина

Волчо

Корчагина

et al. 2007

Helvetica Chimica Acta

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“…An important terpene subgroup is the pinanes with a fused four‐membered ring. We have previously undertaken extensive studies of the 1 H‐NMR spectra of these molecules, confirming their structures and in several cases suggesting their conformations. However, since this early work, there has been no comprehensive attempt to calculate the 1 H chemical shifts of these molecules.…”

Section: Introductionmentioning

confidence: 63%

A molecular mechanics and ab initio prediction of the ¹H chemical shifts of pinanes

Abraham

Cooper

2017

Magnetic Reson in Chemistry

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Molecular mechanics calculations plus the application of a refined Karplus equation gave the conformations of 19 pinanes. These range from a Y-shaped geometry in the apopinene and α-pinene series to a pseudo chair conformation in β-pinene, nopinone and verbanone, a flattened chair in pinocarvone and the pinocarveols and a distorted Y shape for iso-verbanone. These structures were then used as input to predict the H chemical shifts of these compounds by semi-empirical ( H-NMR spectra (HSPEC)) and ab initio gauge-invariant atomic orbital (GIAO) calculations, the latter at the B3LYP hybrid density functional theory level using 6-31++G** basis set. The two methods gave generally good agreement with the 184 observed shifts with root mean square (RMS) errors 0.07 ppm (HSPEC) and 0.10 ppm (GIAO), but the GIAO calculations gave several significant (>0.25 ppm) errors. One was for the H proton in apopinenone and other α,β unsaturated ketones; the others occurred for protons in close proximity to hydroxyl groups. To provide more information, smaller analogues of known geometry and chemical shifts were subject to the same analysis. In cyclopentenone, the Gaussian geometry gave good agreement with the observed shifts, but the MMFF94, MMX and MM3 geometries all gave errors for different protons. These results show clearly that the molecular geometries of the α,β unsaturated ketones are responsible for the errors. The errors for the alcohols were examined using ethanol as model and were shown to be due to the different possible conformations of the OH group. Similar GIAO calculations on substituted methanes gave good agreement for the methyl compounds but poor agreement for di and tri halosubstituted methanes. The aforementioned method of molecular mechanics plus GIAO calculations is shown to be a very useful tool for the investigation of molecular geometries and conformations. However, multihalogen compounds may require different basis sets for accurate calculations. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Abraham et al 27 had originally assigned the 220 MHz 1 H spectrum of a number of bridged cyclobutanes including˛-andˇ-pinene. A number of assignments of the 13 C spectra were given but Coxon et al 28 used C-H coupling, 13 C and 2 H labelling and shift reagent studies to assign unambiguously the 13 C spectra of a number of pinanes.…”

mentioning

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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The NMR spectra and conformations of cyclic compoundsV: Proton couplings and chemical shifts in bridged cyclobutanes

Cited by 39 publications

References 36 publications

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

A molecular mechanics and ab initio prediction of the ¹H chemical shifts of pinanes

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

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The NMR spectra and conformations of cyclic compoundsV: Proton couplings and chemical shifts in bridged cyclobutanes

Cited by 39 publications

References 36 publications

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

Reactions of Allyl Alcohols of the Pinane Series and of Their Epoxides in the Presence of Montmorillonite Clay

A molecular mechanics and ab initio prediction of the 1H chemical shifts of pinanes

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

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A molecular mechanics and ab initio prediction of the ¹H chemical shifts of pinanes