Carbon approach

When two sp2-hybridized carbons approach each other, they form a cr bond by sp2-sp2 head-on overlap. At the same time, the unhybridized p orbitals approach with the correct geometry for sideways overlap, leading to the formation of what is called a pi (ir) bond. The combination of an >p2-sp2 a bond and a 2p-2p 77 bond results iii the sharing of four electrons and the formation of a carbon-carbon double bond (Figure 1.14). Note that the electrons in then-bond occupy the region centered between nuclei, while the electrons in the 77 bond occupy regions on either side of a line drawn between nuclei. 

You might recall from Section 1.9 that a carbon-carbon triple bond results from the interaction of two sp-hybridized carbon atoms. The two sp hybrid orbitals of carbon lie at an angle of 180° to each other along an axis perpendicular to the axes of the two unhybridized 2py and 2pz orbitals. When two sp-hybridized carbons approach each other, one sp-sp a bond and two p-p -rr bonds are... 

In the presence of ZrCU or HC1, cyclization of y - a I k o x y a 11 y I s t a n n a n e 158 bearing (i )-(+)-l-phenylethylamine as a chiral auxiliary occurs to produce trans-fi-aminocyclic ether 159 with high de (91%). As shown in Scheme 3-55, asymmetric addition of an allyl group to the imine carbon can be explained by the modified Cram model 160. The attack of the allylic y-carbon approaches... 

Dr. William W. Jacques further explored the carbon approach in 1896. His fuel cells had a carbon rod central anode in the electrolyte of molten potassium hydroxide. He made a fuel cell system of 100 cylindrical cells, which produced as much as 1500 W. Francis T. Bacon worked on fuel cells to produce alkaline systems that did not use noble metal catalysts in the 1930s. He developed and built a 6 kW alkaline hydrogen-oxygen system in 1959. In the same year, Dr. Harry Ihrig introduced... 

The bottom curve of Fig. 3 shows that acceptor semi-bridging carbonyls bend back as the carbon approaches the second metal (i.e., as the asymmetry decreases) until 9=135° for symmetrically bridged carbonyls. In the second type of interaction, which we denote as "donor semi-bridging", the M-C-0 angle is nearly invariant with respect to the asymmetry parameter. That the carbonyls remain essentially linear when they act in a donor capacity is reasonable when one considers that the oxygen must also approach the metal, M, in structure II. 

L. B. Luo, S. H. Yu, H. S. Qian, and J. Y. Gong, Large scale synthesis of uniform silver carbon rich composite (carbon and cross-linked PVA) sub-microcables by a facile green chemistry carbonization approach. Chem. Commun., (7), 793-795, 2006. 

For the SnI reaction, formation of a carbocation would require that the bridgehead carbon approach frigonal planar geometry, which would lead to a carbocation of extremely high energy due to the geometric constraints of the bicyclic ring. 

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