Hydroboration of cyclic allenes with disiamylborane

1968 ◽  
Vol 46 (15) ◽  
pp. 2632-2634 ◽  
Author(s):  
D. S. Sethi ◽  
G. C. Joshi ◽  
D. Devaprabhakara
Keyword(s):  
Carbon Atom ◽  
Transition State ◽  
Steric Effects ◽  
Terminal Carbon Atom ◽  
Central Carbon Atom ◽  
Central Carbon

It has been shown that 1,2-cyclononadiene and 1,2-cyclotridecadiene undergo 78 and 100% hydroboration respectively, with disiamylborane. 1,2-Cyclononadiene gave products which represented 83% attack of boron at the central carbon atom and 17% attack at the terminal carbon atom. 1,2-Cyclotridecadiene gave 62% central carbon attack and 38% terminal carbon attack. The reactivity and selectivity may be explained mainly in terms of steric effects on a four-centered transition state.

Hydroboration of acyclic allenes with disiamylborane

1969 ◽  
Vol 47 (6) ◽  
pp. 1083-1086 ◽  
Author(s):  
D. S. Sethi ◽  
G. C. Joshi ◽  
D. Devaprabhakara
Keyword(s):  
Carbon Atom ◽  
Transition State ◽  
Steric Effects ◽  
Electrophilic Attack ◽  
Terminal Carbon Atom ◽  
Central Carbon Atom ◽  
Central Carbon

The present investigation demonstrates the hydroboration of 1,2-nonadiene, phenylpropadiene, 3-phenyl-1,2-butadiene, 4,5-nonadiene, and tetramethylallene with disiamylborane. All the allenes except tetramethylallene underwent 100% conversion. Examination of the products indicated preferential electrophilic attack of boron on the least substituted terminal carbon atom in the case of 1,2-nonadiene, phenylpropadiene, 3-phenyl-1,2-butadiene, and on the central carbon atom in 4,5-nonadiene. In tetramethylallene boron, attack was exclusively on the central carbon atom. These results have been explained in terms of steric effects on a four-centered transition state.

scholarly journals 13C—NMR-Spektren und Bindungsverhältnisse von Ketenen / 13C—NMR-Spectra and Bonding Situation of Ketenes

1974 ◽  
Vol 29 (5-6) ◽  
pp. 393-398 ◽  
Author(s):  
Joachim Firl ◽  
Wolfgang Runge
Keyword(s):  
Carbon Atom ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
13C Nmr Spectra ◽  
Terminal Carbon Atom ◽  
Central Carbon Atom ◽  
Central Carbon ◽  
C Nmr

18C-NMR spectra of alkyl- and arylsubstituted ketenes are reported1e. The terminal carbon atom resonances are found at extreme highfield positions ranging from 2.5 ppm to about 50 ppm. They are the most shielded sp2-carbon-atoms observed until now. The central carbon atom resonances appear from about 190 ppm to 206 ppm. From comparisons of the chemical shifts of the ketene carbon atoms with that of analogously substituted alienes and olefines conclusions concerning the bonding situation in ketenes are drawn.

Ab initio charge density analysis of (B6C)2– and B4C3 species — How to describe the bonding pattern?

2006 ◽  
Vol 84 (5) ◽  
pp. 771-781 ◽  
Author(s):  
Cina Foroutan-Nejad ◽  
Gholam Hossein Shafiee ◽  
Abdolreza Sadjadi ◽  
Shant Shahbazian
Keyword(s):  
Quantum Theory ◽  
Carbon Atom ◽  
Charge Density ◽  
Ab Initio ◽  
Atoms In Molecules ◽  
Central Carbon Atom ◽  
B3lyp Method ◽  
Central Carbon ◽  
Density Analysis ◽  
Concrete Ring

In this study, a detailed topological charge density analysis based on the quantum theory of atoms in molecules (QTAIM) developed by Bader and co-workers, has been accomplished (using the B3LYP method) on the CB62– anion and three planar isomers of the C3B4 species, which had been first proposed by Exner and Schleyer as examples of molecules containing hexacoordinate carbon atoms. The analysis uncovers the strong (covalent) interactions of boron atoms as well as the "nondirectional" interaction of central carbon atom with those peripheral atoms. On the other hand, instabilities have been found in the topological networks of (B6C)2– and B4C3(para) species. A detailed investigation of these instabilities demonstrates that the topology of charge density has a floppy nature near the equilibrium geometries of the species under study. Thus, these species seems to be best described as complexes of a relatively concrete ring containing boron or carbon atoms and a central carbon atom that is confined in the plane of the molecule, but with nondirectional interactions with the surrounding atoms.Key words: hypervalency, hexacoordinate carbon, quantum theory of atoms in molecules, charge density analysis, ab initio methods.

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