Extended Hückel Theory. IV. Carbonium Ions

Ab initio/GIAO-MP2-calculated structures and (11)B-(13)C NMR chemical shift relationship in hypercoordinate onium-carbonium dications and isoelectronic onium-boronium cations.

The boronium-carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-boronium cation analogs. Structures and (13)C and (11)B NMR chemical shifts of the onium-carbonium dications and the corresponding isoelectronic and isostructural onium-boronium cations were calculated with the ab initio/GIAO-MP2 method. The data show a good linear...

Origin of the minimum in the total energy curve of diamond using the extended Hückel theory

The Role of Carbonium Ions in Color Reception

It is a fundamental property of conjugated systems to accept a proton or Lewis acid and form a stable carbonium ion. Polyenes that are protonated or add Lewis acids in this manner undergo substantial red shifts. For example, vitamin A(1) acetate absorbs at 350 mmicro in neutral and at 650 mmicro in acidic benzene solution. The fundamental basis for absorption of polyene systems was described in...

Carbonium vs. carbenium ion-like transition state geometries for carbocation cyclization - how strain associated with bridging affects 5-exo vs. 6-endo selectivity.

Quantum chemical calculations are used to explore the origins of regioselectivity for proton-, Pt(II)- and Pd(II)-promoted cyclizations of 1,5-hexadienes, 5-aminoalkenes, and allylic acetimidates. The strain associated with achieving carbonium ion-like transition state geometries is shown to be a key factor in controlling 5-exo vs. 6-endo selectivity.

Stabilised Carbonium Ions in the Organic Chemistry of Platinum THE EVIDENCE FOR THEIR EXISTENCE

Historically, platinum has played a prominent role in organometallic chemistry. The compounds KPtCI,(C,H,)H,O (I), PtMe, (X) (2) and Chugaev's salt [PtC,H,,N,],Clx (3, 4) present some of the fist examples of stable metal-olefin, metal-alkyl and metalcarbene complexes, although ironically the nature of the bonding in these compounds was not immediately recognised. In the study of organometallic ...