7-Syn- and 7-anti-proton absorptions in the nuclear magnetic resonance spectra of norbornenes

Franzus, Boris; Baird, William C.; Chamberlain, Nugent F.; Hines, T.; Snyder, Eugene I.

doi:10.1021/ja01016a022

Cited by 55 publications

(14 citation statements)

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“…Deuteration studies 6 unambiguously assigned the 7-syn protons in norbornene to lower field than the 7-anti proton, contrary to Jackman's theory. A later investigation of olefinic shielding was due to ApSimon et al 7 They derived comparable values for the parallel z y and perpendicular x y anisotropies of the double bond but concluded that 'the conventional picture of a shielding cone around the C C bond appears to require substantial modification.…”

Section: Introductioncontrasting

confidence: 63%

“…This option on iterating the parameters gave values of 20.09Å 3 for the anisotropy (i.e. 12.1 ð 10 6 cm 3 mol 1 ) and 82.5Å 6 for the shielding shifts together with the effects of Table 2. For the data set considered of 172 chemical shifts in Tables 3-7 spanning a range of ca 0.5-8.4υ the CHARGE7 scheme fits the experimental data to an r.m.s.…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Introductioncontrasting

confidence: 63%

Section: Resultsmentioning

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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“…Calculations using the McConnell equation, as modified by Nakagawa, revealed that (1) the axes of the 2,3‐π orbitals of 2‐norbornene are essentially parallel to the C 7 ‐H 7syn bond and (2) H‐7syn is located near the edge of the shielding cone, which corresponds to the magic‐angle cone (55° 44′) of solid‐state NMR spectroscopy. This location suggests that H‐7syn may be slightly shielded or deshielded in norbornenes, and that its chemical shift depends on the degree to which various substituents slightly deform the norbornyl molecule and thus move H‐7syn toward, or away from, the shielding cone . It should also be noted that shielding effects regarding H‐5,6exo (δ 1.61) and H‐5,6endo (δ 0.96) are reversed from those described above for H‐7syn (deshielded) and H‐7anti (shielded).…”

Section: Introductionmentioning

confidence: 73%

“…Spin‐decoupling experiments clearly differentiated H‐7syn from H‐7anti, as the former displays a very large and distinctive 4‐bond, W‐coupling to the 5,6‐endo protons in the range of 2.0 to 2.5 Hz. These results clearly indicated that (1) the chemical shifts of H‐7syn and H‐7anti were δ 1.32 and δ 1.03, respectively, and (2) that while H‐7syn was on the same side of the norbornenyl molecule as the 2,3‐double bond, it was not the more shielded proton . It should be noted that proton NMR spectra of 2‐norbornene were recorded by early investigators in carbon tetrachloride and benzene, as well as chloroform, which has resulted in a small spread of observed chemical shift values.…”

Section: Introductionmentioning

confidence: 82%

The shielding effect of the double bond in 2‐norbornene and α‐pinene and β‐pinene

Mazzola

Lambert

Ridge

2018

J of Physical Organic Chem

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“…Wie Vergleichswerte zeigen [4] [5], wird die Kopplung offenbar durch die n-Elektronen des Benzolrings verstarkt. Man findet sie auch zwischen den syn-, nicht aber den anti-Protonen an C(3) und C(9) (vgl.…”

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Derivate des 5, 9‐Methano‐6, 7,8, 9‐tetrahydro‐5 H‐benzocycloheptens und Umlagerungen zum 1, 4‐Äthano‐1,2,3,4‐tetrahydronaphtalin‐System

Stoll

Loosli

Niklaus

et al. 1978

Helvetica Chimica Acta

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Derivatives of 5,9-Methanod,7,8,9-tetrahydro-5H-benzocycloheptene and Rearrangements to the 1,4-Ethano-I,2,3,4-tetrahydronaphthalene System SummaryReduction of the oxime 2 with Raney alloy gives the amine 3a, with A1H3 a mixture of the isomeric amines 3a and 3b, whilst LiAIH, yields the aziridines 4a and 4b. The bicyclo [3.2.l]octane 4b rearranges under acidic conditions to the bicyclo[2.2.2]octane 5. The olefin 7 can be converted to the aminoalcohol 9 via the epoxide 8 and to the amine 13 using iodine isocyanate: the carbon skeleto. remains intact. However, treatment of the olefin 17 with iodine isocyanate leads to the bicyclo[2.2.2]octanes 21 and 24 in which a skeletal rearrangement has taken place. The configuration was determined by NMR. and X-ray analysis.Ausgehend vom leicht zuganglichen Keton 1 [ l ] bildet sich uber das Oxim 2 mit Hilfe von Raney-Legierung unter alkalischen Bedingungen regioselektiv das endo-Amin 3a, hingegen mit Aluminiumhydrid ein Isomerengemisch 3a/3 b im Verhaltnis 1: 1 (Schema 1). Mittels der NMR.-Signale kann die Konfiguration dieser beiden Amine leicht abgeklart werden. Die Lage der Aminprotonen in 3a bei sehr hohem Feld (6=0,3, CDC13) ist der Anisotropie des Benzolrings zuzuschreiben'). Die chemische Verschiebung (6 = 3,l) des H-C(7) jedoch ist normal. Daraus schliessen wir, dass die Aminogruppe endo steht. Die NMR.-Daten von 3b (NH, bei 2,15, H-C(7) bei 2,0-2,5) zeigen, dass dieser Verbindung die exo-Struktur zukommt.Wird das Oxim 2 mit Lithiumaluminiumhydrid reduziert, so bildet sich ein Gemisch der isomeren Aziridine 4a (endo) und 4b (exo) [3]. Kurzes Erwarmen von 4b in 4~ HC1 fuhrt in 50% Ausbeute zu einem chlorierten Umlagerungsprodukt 5, dessen Struktur mit Hilfe der NMR.-Daten abgeklart wurde. Es zeigte sich, dass 5 nicht mehr das Bicyclo [3.2.l]octan-Geriist, sondern das Bicyclo [2.2.2]0ctan-Gerust besitzt. Beim [3.2.l]-Geriist ist der Cyclohexanring so deformiert, dass die Bruckenkopfprotonen praktisch nicht mehr mit dem axialen Proton der Methanobrucke ') Im gleichen Ringsystem wurde dieser Effekt schon von Shupiro et al. [2] beschrieben.

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7-Syn- and 7-anti-proton absorptions in the nuclear magnetic resonance spectra of norbornenes

Cited by 55 publications

References 1 publication

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

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

The shielding effect of the double bond in 2‐norbornene and α‐pinene and β‐pinene

Derivate des 5, 9‐Methano‐6, 7,8, 9‐tetrahydro‐5 H‐benzocycloheptens und Umlagerungen zum 1, 4‐Äthano‐1,2,3,4‐tetrahydronaphtalin‐System

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