For ring protons

Table 7 11, H Coupling Constants for Ring Protons in Furan Derivatives...

The ring system, which has an axis of symmetry, consists of two interchangeable ortho, two interchangeable meta protons, and one para proton, all in the characteristic region for ring protons. The alert student, having absorbed the concept of chemical-shift equivalence, (Section 3.8.3) and the description of the... 

As shown in Fig. (7), the relative configurations for the diastereo-meric adducts were determined by NOESY correlations and coupling constants for ring protons. All the IMDA reactions proceeded with high endo/exo selectivity (A+B/C+D), while the n-facial selectivity of the endo-adducts (A/B) depended on the protecting group at C-l. The C-l alkyl- and acyl-protected substrates (88, 95, or 96) and non-protected substrate 89 provided the undesired cycloadduct B preferentially... 

On the other hand, the acid pK of the carboxylic group of the substrate is 5.5, and the pK s for ring protonation of the azulene system and for O protonation of the COOH group are known to be negative (application of the H0 scale, see Vol. 2, p. 358). Consequently, the coefficient with a value of 3.8 x 10-2 mole. I"1 in the denominator of eqn. (13) cannot be an ionization constant of the substrate, and it must have another meaning. An explanation of the experimental findings is offered on the basis of the mechanism... 

The NMR spectrum for phenazine shows an AA BB system for ring protons at <5 7.97 and 8.26 ppm in [ H Jdimethyl sulfoxide and coupling constants (Jj j = 9.0 Hz Jj 3 = 1.67 Hz Ji.i = 6.55 Hz) have been estimated. Similar coupling constants are also characteristic for substituted phenazines and phenazine A -oxides. H and CNMR data for phenazine and substituted phenazinesand CNMR spectra for phenazine di-A-oxide have been measured and assigned. NNMR data have also been reported for phenazine.Tire high resolution NMR spectra of phenazine have been measured in inert and proton donating solvents. 

Table 2 H NMR data for ring protons of 1,3-dioxolane derivatives.

Least Squares Linear Regression Analysis of VT H NMR Data for Ring Protons in Uranocene, Octamethyluranocene and the Unsubstituted Ring in Monosubstituted Uranocenes. 

As a result of Xjj 0, early work on factoring the isotropic shift of the ring protons in uranocene underestimated the magnitude of the contact shift. Using our value of Uj2 yj = 12.5 BM2, the pseudocontact and contact shifts for uranocene ring protons are -8.30 ppm and -34.2 ppm, (G = -2.34 x 1021 cm-3), respectively. Thus, this study confirms that both contact and pseudocontact interactions contribute to the observed isotropic shifts in uranocenes. The contact component is dominant for ring protons, but rapidly attenuates with increasing number of Q-bonds between the observed nucleus and the uranium such that the contact shift is effectively zero for g-protons. 

A sharply defined line for the proton signal, not broadened by nitrogen quadrupolar relaxation, is seen for 1,3,5-triazine at 9.18 ppm, which is well downfield of the chemical shift of the benzene proton. The presence of electron-releasing substituents gives slight upheld shifts for ring protons of substituted 1,3,5-triazines. Chemical shifts of 8.8 ppm, 8.51 ppm, and 8.19 ppm are seen for... 

Proton NMR data for thiocane (2) consists of adsorptions expected for aliphatic, cyclic thioethers 1.2-1.5 for ring protons on carbons not alpha to sulfur and 2.5-3.0 <5 for protons on carbons alpha to sulfur <80JOC3613>. Benzo fusion, (18), shifts the protons of the alpha carbon down slightly (3.13 d), along with the protons beta to ring fusion and beta to sulfur (1.65-1.77 S) <82ACS(B)561>. Proton spectra for thiocins and their nonconjugated, or partly-reduced, derivatives are typical of unsaturated, nonaromatic, cyclic thioethers. 

Fig. 3 - Newman projections for ring protons of iduronic acid (I a,b,Ctd) and protons at Cg of aminosugar (A,e)...

The solid-state structure of 18 is similar to the iridabenzenes reported earlier by Bleeke (vide supra). The coordination geometry is a distorted square pyramid with the small CO ligand occupying one of the basal sites. The ring is essentially planar, and the TT-bonding is delocalized (see Table 1). The H NMR spectrum shows the expected downfield shifting for ring protons HI. H2. and H3 (see Table 2). Compound 18 is air stable but does react with maleic anhydride to produce a [4+2] cycloaddition product. 

Many similarities exist between metallabenzenes and conventional arenes. Among these similarities are structural features such as ring planarity and the absence of bond length alternation, spectroscopic features such as downfield chemical shifts for ring protons, and chemical reactions such as electrophilic aromatic substitution and arene displacement from (arene)Mo(CO)3. All of these features, taken together, strongly support the thesis that metallabenzenes represent a new class of aromatic compounds, one in which metal d orbitals participate fully with carbon p orbitals in the formation of ring 7r-bonds. 

NMR spectra at room temperature for ring protons shows a singlet... 

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