Dynamic proton magnetic resonance studies on complex spin systems. Non‐mutual three‐spin exchange in four 1‐substituted cyclohexanes‐2,2,3,3,4,4,5,5‐d8 and mutual four‐spin exchange in cyclohexane‐1,1,2,2,3,3,4,4‐d8

Hofner, Dieter; Lesko, Susan A.; Binsch, Gerhard

doi:10.1002/mrc.1270110405

Cited by 94 publications

(20 citation statements)

References 62 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The large difference in the chemical shifts of cyclohexane compared with those in Ref. 22 is noteworthy and is due to the anisotropic CS2 solvent used in Ref. 22.…”

Section: Nmr Spectramentioning

confidence: 87%

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

Abraham

Fisher

1985

Magnetic Reson in Chemistry

View full text Add to dashboard Cite

The molecular geometries and proton N M R spectra of norbornene, norbornane and adamantane are reported. The molecular geometries were refined from previous experimental determinations using MNDO and ab initio techniques to determine the positions of the hydrogen atoms. No evidence of any endo-endo interactions in norbornane was obtained from these calculations.High-field proton NMR spectra allow the refinement of previous spectral analyses of adamantane and norbornane, and the complete analysis of the olefin decoupled eight spin system of norbornene.

show abstract

“…The large difference in the chemical shifts of cyclohexane compared with those in Ref. 22 is noteworthy and is due to the anisotropic CS2 solvent used in Ref. 22.…”

Section: Nmr Spectramentioning

confidence: 87%

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

Abraham

Fisher

1985

Magnetic Reson in Chemistry

View full text Add to dashboard Cite

show abstract

“…To obtain a consistent set of data we used the splitting between the methine proton at C2 and the trans proton at C3 as Jobs. For this interaction it was necessary to modify the values for J,, and Jee to include the electronegativity effect of the methoxyl (18). Accordingly, the value for J,, was reduced to 12.0 Hz and that for J,, raised to 2.7 Hz.…”

mentioning

confidence: 99%

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Fraser¹,

Faibish²

1995

Can. J. Chem.

View full text Add to dashboard Cite

Abstract:The value for the equilibrium constant representing the ratio of equatorial to axial conformers for 2-methylthio-and 2-methoxycyclohexanone has been measured in five solvents using 500 MHz 'H nuclear magnetic resonance. In cyclohexane solvent, the methylthio group is found to have a large axial preference while that for the methoxy is negligible. For both compounds the equilibrium shows a strong solvent dependence.Comparison of these results with those known for the halo derivatives shows the amount of axial to increase in the order: fluoro, methoxy, chloro, bromo, and methylthio. With the aid of molecular mechanics calculations it is concluded that the order of conformational preference can be attributed to a variation in the van der Waals interaction between the substituent and the carbonyl group in the equatorial conformer.Key words: a-substituted cyclohexanones, conformation, MMX calculations, steric and dipolar effects.Resume : Utilisant la rksonance magnCtique nuclCaire du 'H a 500 MHz et opCrant dans cinq solvants, on a mesurC la valeur de la constante d'tquilibre reprksentant le rapport des conformkres Cquatorial et axial des 2-mCthylthio-et 2-mCthoxycyclohexanones. Dans le cyclohexane comme solvant, on trouve que le groupe mtthylthio a une prCfCrence axiale alors que celle du groupe mCthoxy est negligeable. Pour les deux composts, 1'Cquilibre depend fortement du solvant. Une comparaison de ces rCsultats avec ceux connus pour les dCrivCs halogCnCs montre que la quantitC de conformkre axial augrnente dans l'ordre : fluoro, mCthoxy, chloro, bromo et rntthylthio. En se basant sur des calculs de mCcanique molCculaire, on conclut que l'ordre de prCftrences conformationnelles peut Etre attribuC a une variation de l'interaction de van der Waals entre le substituant et le groupe carbonyle du conformkre Cquatorial.

show abstract

“…For example, the data in Table 2 (6,(14)(15)(16) show that the equatorial preference of cyclohexylmethyl sulfide is higher than that of the heavy halogen and methoxy substituents. But when the SCH3 substituent interacts with a vicinal polar 0CH3 substituent, as in trans-1 -methylthio-2-methoxycyclohexane, a conformational population change occurs that is larger than predicted on steric grounds (32% of axial conformation in CC14, -AGO = 0.4 kcal/mol) (6).…”

Section: Discussionmentioning

confidence: 99%

Repulsive gauche conformational effect. Analysis of seven-membered rings containing endo and exo sulfur atoms

Dionne¹,

St‐Jacques²

1990

Can. J. Chem.

View full text Add to dashboard Cite

The so-called repulsive gauche conformational effect associated with sulfur is investigated through a study of 3-methylthio-1,5-benzodioxepin (1) and 3-methylthio-1-benzoxepin (2), together with 3-fluoro-and 3-chloro-l,5-benzodithiepins (3 and 4), by I3C and 'H dynamic nuclear magnetic resonance methods. The results show that, while compounds 2 , 3 , and 4 exhibit a large amount of the C, conformation, the TB form predominates for compound 1. intramolecular stereoelectronic u-u* orbital interactions are analyzed, together with several other factors (steric, electrostatic, and solvation), to explain the observed conformational behaviour.Key words: gauche effect, seven-membered rings, 1,5-benzodithiepins, variable temperature NMR, orbital interactions.On a ttudit l'effet conforrnationnel gauche repulsif associt ii l'atome de soufre en examinant la 3-mCthylthio-l,5-benzodioxCpine (I), la 3-methylthio-1-benzoxtpine (2) ainsi que les 3-fluoro-et 3-chloro-l,5-benzodithitpines (3 et 4), par des mCthodes de rCsonance magnCtique nucliaire dynamique du I3C et du IH. Les rksultats dtmontrent que, alors que l'on dttecte la prisence de quantitts importantes de la conformation C, dans les composts 2 , 3 et 4, la forme TB prkdomine pour le composC 1. On a analyst les interactions stCrtoClectroniques intramolCculaires des orbitales u-u* ainsi que plusieurs autres facteurs (stCrique, tlectrostatique et de solvatation) afin de pouvoir expliquer le comportement conforrnationnel observt.Mots clks : effet gauche, cycles ii sept chainons, 1,5-benzodithitpines, RMN 2i temp6rature variable, interactions orbitales.[Traduit par la revue] Introduction Over the last few years, we have been interested in the mechanism of the gauche effect (1) and the underlying molecular interactions as revealed by the conformational analysis of some 3-substituted 1,5-benzodioxepins (2, 3) and 1-benzoxepins (4, 5). These results have shown that the seven-membered heterocycles can provide information complementary to analogous six-membered molecules because of the greater ring flexibility, giving rise to the twist boat (TB) form in addition to the axial chair (C,) and the equatorial chair (C,) conformations. Such studies unravelled the nature of the molecular orbital interaction involved. According to the rationalizations formulated earlier by Zefirov et al. (6) from studies of six-membered ring molecules, the conformational feature of the oxygen-containing seven-membered rings studied (2-5) was characteristic of attractive or negligible gauche effects. Our present aim is to analyze the repulsive gauche effect (6, 7) through the conformational study of seven-membered rings containing erzdo and exo sulfur atoms interacting with other heteroatoms such as in the series 1-6.

show abstract

Dynamic proton magnetic resonance studies on complex spin systems. Non‐mutual three‐spin exchange in four 1‐substituted cyclohexanes‐2,2,3,3,4,4,5,5‐d₈ and mutual four‐spin exchange in cyclohexane‐1,1,2,2,3,3,4,4‐d₈

Cited by 94 publications

References 62 publications

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

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

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Repulsive gauche conformational effect. Analysis of seven-membered rings containing endo and exo sulfur atoms

Contact Info

Product

Resources

About