Ring proton

Like other strong nucleophiles, Grignard and organolithium reagents attack epoxides to give (after protonation) ring-opened alcohols. 

Fig. 4.3. Part of the 1H NMR spectra of L and its 1 1 and 1 2 complexes with Lam in CD3CN at 298 K displaying the signals of the methylene protons (ring, Ha and He arm, Hp). (Reproduced with permission).

There are two absorptions in the NMR spectrum of p-xylene. The four ring protons absorb at 7.0 5, and the six methyl-group protons absorb at 2.3 8. The peak ratio of methyl protons ring protons is 3 2. 

Occasionally, displacements occur in the process of reacting oxoazines with phosphorous oxychloride or pentasulfide or with an arylsulfonyl halide, thionyl chloride, or sulfuryl halide. The phos-phoryloxy or sulfonyloxy intermediates (201) are now activated by virtue of the protonated ring-nitrogen plus the electron-attracting acyloxy substituent. 

Benzene cannot be obtained directly from / ara-protonated aromatic rings in the polymer. However, j>ara-protonated rings can react with neighboring polymer chains to yield the same chain scission products that are formed by orf/zo-protonation. 

In the usual SjsjZ (A 2) mechanism, the reaction of the water molecule with the protonated compound is rate determining, while in the pure S l (A 1) mechanism, the unimolecular opening of the protonated ring is rate determining. Discussing the mechanism of the polymerization of isobutylene oxide it was eventually concluded that stereochemical studies would be needed to distinguish between these possibilities. 

Branching isomerization of long-chain n-alkanes on Pt/H-USY zeolites occurs primarily via substituted protonated cyclopropane (PCP) intermediates (300), with a minor contribution of larger protonated rings (301). The di- and tribranched carbocations are particularly susceptible to undergo /3-scission to cracked products. Various paths of isomerization and /3-scission are outlined in Fig. 24. 

In the first step, the carbon centered radical is generated. The second step involves the addition of this radical to the protonated ring. The third step consists of the rearomatization of the radical adduct by oxidation. The rates of addition of alkyl and acyl radicals to protonated heteroaromatic bases are much higher than those of possible competitive reactions, particularly those with solvents. Polar effects influence the rates of the radical additions to the heteroaromatic ring by decreasing the activation energy as the electron deficiency of the heterocyclic ring increases. 

If such reactions with base are carried out at elevated temperatures, a-methyl ketones are obtained by protonative ring opening of the initially formed cyclopropanols.The importance of the proper choice of reaction conditions is well-demonstrated in the reaction of siloxycyclopropane 19. A cyclic ketone containing two quaternary carbons 20 can be obtained by employing more forcing conditions. On the other hand, similar reaction with shorter reaction time gives desilylated compound 21 as a major product. 

The cyclic imino protons (ring N-H) of pyrimidine and purine rings resonate at 12.5 2.5 ppm. 

This conclusion can also be extended to the protons located near the plane of the protonated ring, in particular, to those of the CH3 groups of methylbenzenium ions. Indeed, estimation of anisotropic effects according to the semiempirical method suggested by J. Goldstein and G. Reddy indicates the ring anisotropy of... 

CH3 (3.1-3.6) and 2-CH3 (2.S-3.2 ppm). The introduction of a CH3 group to 4-position was observed to cause a down-field shift of the H signal by 0.5 ppm The spin-spin coupling constants for the protonated ring of 1-H-naphthalenium ions have the following values ... 

Thus, a thin proton ring with full field reversal = 2 and... 

Phys. Rev. Lett. 46 539 (1981) "Formation and Dynamics of a Rotating Proton Ring in a Magnetic Mirror", Cornell University Laboratory of Plasma Studies Report 290 (1981)... 

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