Data for ring protons

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. 

Table 4 Proton NMR spectral data for ring hydrogens of 1,2,3-thiadiazoles...

Larsson et al. 92) demonstrated also that the anisotropic pseudorotation model could be used for direct fitting of experimental PRE data for aniline protons in the complex between a Ni(II) chelate (Ni(II)(dpm)2) and ring-deuterated aniline in toluene-dg solution. The Ni(II) ion is in this case surrounded by four oxygen atoms and two nitrogen atoms, which should result in a sizable static ZFS, which indeed is confirmed by the fits. 

Typical proton and 13C chemical shift data for ring atoms of dioxetanes from the last decade are collated in Figure 1. For spectral data prior to this, see CHEC-II(1996) <1996CHEC-II(1B)1041>. 

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. 

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. 

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

NMR data for 4-methyloxazole have been compared with those of 4-methylthiazole the data clearly show that the ring protons in each are shielded. In a comprehensive study of a range of oxazoles. Brown and Ghosh also reported NMR data but based a discussion of resonance stabilization on pK and UV spectral data (69JCS(B)270). The weak basicity of oxazole (pX a 0.8) relative to 1-methylimidazole (pK 7.44) and thiazole (pK 2.44) demonstrates that delocalization of the oxygen lone pair, which would have a base-strengthening effect on the nitrogen atom, is not extensive. It must be concluded that not only the experimental measurement but also the very definition of aromaticity in the azole series is as yet poorly quantified. Nevertheless, its importance in the interpretation of reactivity is enormous. 

UV spectrum changes dramatically. The salt causes maxima at 251 (4.16), 286 (4.16), 387 (3.56), and 473 (3.37) nm. NMR data for a sample in CF3COOD were presented. It is interesting to note that the nonmethylated derivatives of 130 and 131 are present in solution above pH 6.5 as betaines, forming a protonated pyridine ring and an olate group (91MI3). 

Single- and double-selective relaxation-rates, together with n.O.e. experiments, have been used to examine the configuration and conformation of asperlin (1) in benzene solution." " Comparing experimental distances for the proton pairs H-4,H-7 and H-5,H-7 with those obtained from molecular models, it was possible to confirm earlier evidence that the oxirane ring is trans, and also to show that, of the two possible diastereoisomeric forms (49a and 49b), the data are more fully compatible with structure 49a, the... 

After what we have seen to date, it surely comes as no great surprise to find that the ratio of o- to p-product obtained from substitution of C6H5Y, where Y is o-/p-directing, is seldom, if ever, the statistical ratio of 2 1. There is found to be very close agreement between calculation and n.m.r. data for the distribution of +ve charge—p-> o- m—around the ring in the cyclohexadienyl cation (57), which is the Wheland intermediate for proton exchange in benzene (cf. p. 133) ... 

The first obvious deduction is that the compound must be an ethyl ester rather than an ethyl ether as the -CEE correlates to a carbonyl carbon at 165 ppm. No other protons correlate to this carbon so even without any 13C prediction, the ethyl ester is confirmed. The relative positions of the ester and methyl substituents are confirmed as if they were reversed, a common correlation from both the methyl protons and the indole 7 proton to one of the ring junction carbons (127.7 ppm in this compound) would be expected. Finally, the position of the -OH is confirmed by comparison with 13C prediction data for both the 5 and the 6 isomer and by the weak but significant correlation from the 4 proton to the 3 carbon at 102 ppm. Note that correlations from the -OH in this case are a bonus. Exchangeable signals are often too broad to give useful correlations. 

Fig. 5 Logarithmic plots of rate-equilibrium data for the formation and reaction of ring-substituted 1-phenylethyl carbocations X-[6+] in 50/50 (v/v) trifluoroethanol/water at 25°C (data from Table 2). Correlation of first-order rate constants hoh for the addition of water to X-[6+] (Y) and second-order rate constants ( h)so1v for the microscopic reverse specific-acid-catalyzed cleavage of X-[6]-OH to form X-[6+] ( ) with the equilibrium constants KR for nucleophilic addition of water to X-[6+]. Correlation of first-order rate constants kp for deprotonation of X-[6+] ( ) and second-order rate constants ( hW for the microscopic reverse protonation of X-[7] by hydronium ion ( ) with the equilibrium constants Xaik for deprotonation of X-[6+]. The points at which equal rate constants are observed for reaction in the forward and reverse directions (log ATeq = 0) are indicated by arrows.

Carbon-13 NMR is often a more useful tool than H NMR for the elucidation of heterocyclic structures in which there are few or no ring protons. For symmetrically substituted 1,2,3-thiadiazoles, the carbon adjacent to the nitrogen atom is expected to have a lower field chemical shift than the carbon atom adjacent to the sulfur atom, as exemplified in CHEC-II(1996) <1996CHEC-II(4)289>. Several examples that follow this rule are illustrated in Table 5. There is now a more extensive body of data available and it is possible to more accurately predict the chemical shift of ring carbons. In the case of monosubstituted 1,2,3-thiadiazoles, the substituted carbon usually has a lower field chemical shift than the unsubstituted carbon. 

Model computational studies aimed at understanding structure-reactivity relationships and substituent effects on carbocation stability for aza-PAHs derivatives were performed by density functional theory (DFT). Comparisons were made with the biological activity data when available. Protonation of the epoxides and diol epoxides, and subsequent epoxide ring opening reactions were analyzed for several families of compounds. Bay-region carbocations were formed via the O-protonated epoxides in barrierless processes. Relative carbocation stabilities were determined in the gas phase and in water as solvent (by the PCM method). 

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