Mechanism of aromatic bromination by hypobromous acid in aqueous perchloric acid. Kinetic evidence against the prior formation of ‘positive bromine’

1973 ◽  
pp. 1321-1327 ◽  
Author(s):  
H. M. Gilow ◽  
John H. Ridd
Keyword(s):  
Perchloric Acid ◽  
Hypobromous Acid ◽  
Aqueous Perchloric Acid ◽  
Aromatic Bromination

Participation of 19-substituents in electrophilic additions to 6,7-unsaturated 5α-cholestane and B-homo 5α-cholestane derivatives; A case of competition between the participation of an ambident neighboring group and external nucleophile attack

1980 ◽  
Vol 45 (2) ◽  
pp. 559-583 ◽  
Author(s):  
Pavel Kočovský ◽  
Ladislav Kohout ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Cyclic Ether ◽  
Cyclic Ethers ◽  
Neighboring Group ◽  
Acid Cleavage ◽  
Neighbouring Group Participation ◽  
Aqueous Perchloric Acid ◽  
The Difference ◽  
Electrophilic Additions

Hypobromous acid action upon the 6,7-unsaturated 19-substituted 5α-cholestans Va-Vc results in the formation of two types of products, the cyclic ethers IX as products of 5(O)n participation of the 19-substituent, and the bromohydrins X. All these compounds are formed from the 6α,7α-bromonium ions Va'-Vc'. Under the same conditions the B-homo-5α-cholestane derivatives VIIa-VIIc afforded solely the cyclic ethers XIV as products of 5(O)n participation of the 19-substituent in the cleavage of the bromonium ions VIIa'-VIIc'. Acid cleavage of the 6α,7α-epoxides VIb and VIc with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the cyclic ethers XI and the diols XII or bromohydrines XIII. The cyclic ethers XI arise by 5(O)n participation of the 19-substituent. The B-homo-6α, 7α-epoxide VIIIc on cleavage with aqueous perchloric acid have solely the cyclic ether XVc and by treatment with hydrobromic acid VIIIc afforded the mixture of XVc, as the main product, and of the bromohydrin XVIc. Discussed is the similarity of the bromonium ion cleavage with the fission of the corresponding epoxides, the mechanism of these reactions and the difference in the behaviour of the isomeric olefins Ia-c, IIIa-c, Va-c and VIIa-c and epoxides IIb,c, IVb,c, VIb,c and VIIIb,c. The competition between ambident neighbouring group participation and external nucleophile attack is discussed as well as the dependence of the products ratio on the nucleophilicity of the attacking species.

15N N.M.R. Study of Some Palladium(II) Ammine Complexes

1988 ◽  
Vol 41 (9) ◽  
pp. 1425 ◽  
Author(s):  
TG Appleton ◽  
JR Hall ◽  
SF Ralph ◽  
CSM Thompson
Keyword(s):  
Perchloric Acid ◽  
Chemical Shifts ◽  
Free Ammonia ◽  
Silver Ion ◽  
Single Peak ◽  
Donor Atom ◽  
Ammine Complexes ◽  
Initial Product ◽  
Aqueous Perchloric Acid ◽  
Dimethylformamide Solution

Palladium(II) ammine complexes enriched in 15N give sharp singlets in their 15N n.m.r . spectra. The 15N chemical shifts depend primarily on the trans donor atom, in a qualitatively similar way to those for platinum(II) ammine complexes. A dimethylformamide solution of Pd(NH3)2Cl2 prepared in the usual way gave a single peak, consistent with the presence of only one isomer (trans). Reactions of increasing amounts of aqueous perchloric acid with Pd(NH3)42+ allowed peaks to be identified for Pd(NH3)3(H2O)2+, cis -Pd(NH3)2(H2O)22+ and Pd(NH3)(H2O)32+. The initial product of the reaction of trans-Pd(NH3)2Cl2 with silver ion is trans-Pd(NH3)2(H2O)22+, which rapidly disproportionates to Pd(NH3)3(H2O)2+ and Pd(NH3)(H2O)32+. With standing, subsequent reactions ultimately produce a solution containing predominantly cis -Pd(NH3)2(H2O)22+ in equilibrium with small amounts of the tri- and mono-ammine complexes, and free ammonia.

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