Proton A-ring

Reference to the deshielding of a ring proton by an ortho carboxy group clarifies the assignment. 

In an analogous fashion to that described for hydroxide ion in Section 4.16.5.1, amines will cause the fragmentation of 1,2,4-trioxolanes which have a ring proton. In fact, triethylamine has been... 

Fig. 3. — 400-MHz, H-N.m.r. Spectra of l,2,3,4,6-Pentra-0-acetyl-5-deoxy-5-C-[(R)-ethylphosphinyl]-/ -D-glucopyranose (134). [(a) Ring-proton signals without decoupling, and (b-e) those with decoupling, on irradiation at H-5 (b), at H2-6 (c), at H-4 (d), and at H-3 (e).]...

Semiempirical VB and MO plus Cl calculations by McConnell and others yielded the following theoretical equation for aH, the coupling constant (in units of gauss) between the unpaired n electron and a ring proton of an aromatic radical18 ... 

All the protons in benzene are equivalent. In diphenylmethane and in triphenylmethane, protons are attached either to the. v/r-hybridized carbons of the ring or to the v/T-hybridized carbon between the rings. The large difference in acidity between diphenylmethane and benzene suggests that it is not a ring proton that is lost on ionization in diphenylmethane but rather a proton from the methylene group. 

Reaction occurs in two steps addition of an electrophile to the aromatic n electron system followed by loss of a ring proton. 

Reaction of the heteroannular diol (30) with phenylisocyanate or p-methoxyphenylisocyanate at room temperature gave the expected urethans, but use of these isocyanates at elevated temperature or use of p-nitrophenylisocyanate at room or elevated temperature gave the bridged amine (31 R = H, OCHs, and N02)18 The NMR spectrum of 31 shows a triplet for the ferrocene ring protons.19 This triplet is attributed to the direct inductive influence on the a-ring proton of the bridge nitrogen atom. 

As expected from the electronic structure, the 1,2,5-thiadiazoles readily undergo nucleophilic attack (see also Section 4.02.1.6). The site of attack, however, is variable and can take place either at carbon, sulfur or a ring proton (Scheme 1 also see Section 4.26.3.3.6). 

Average Chemical Shifts (5) and their Difference (A<5) of a Ring Protons in 4-Azaazulenones (5-8) ... 

The chlorosulfated glycosyl chloride 60 is converted into 2-chloro-2-deoxy-a-D-lyxopyra-nosyl chloride 61 when treated with aluminum chloride (O Scheme 34) [58]. This reaction proceeds via an initial intramolecular displacement of chlorosulfate at C-2 by the anomeric chlorine atom, followed by the chloride ion attack at the more highly reactive center (C-1). Pyranoid derivatives having a chlorosulfonyloxy group in a frawi -diaxial relation with a ring proton, such as 62, may undergo an elimination reaction to yield the unsaturated compound 63 (O Scheme 35) [59]. 

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