C-H Bond Formation

Fluorinated alkenes can insert into C-H bonds at elevated temperatures, a relatively unusual example of simultaneous C-C and C-H bond formation [20, 21] (equations 16 and 17)... 

Ethylene is a simple compound of carbon and hydrogen with the formula QH4. Thus it has two less hydrogen atoms than does ethane, QH6. This means that to write a structure of ethylene we must take account of two electrons that are not used in C—H bond formation. Suppose we write an electron dot representation involving only single bonds... 

The insertion of a carbene into a Z-H bond, where Z=C, Si, is generally referred to as an insertion reaction, whereas those occurring from Z=0,N are based on ylide chemistry [75]. These processes are unique to carbene chemistry and are facilitated by dirhodium(II) catalysts in preference to all others [1, 3,4]. The mechanism of this reaction involves simultaneous Z-H bond breaking, Z-car-bene C and carbene C-H bond formation, and the dissociation of the rhodium catalyst from the original carbene center [1]. 

When C—H bond formation occurs, the result is inversion. Racemization results in polar aprotic solvents such as DMSO. In these solvents the carbanions are rela-... 

Hydroboration is a stereospecific syn addition that occurs through a four-center TS with simultaneous bonding to boron and hydrogen. The new C—B and C—H bonds are thus both formed from the same face of the double bond. In molecular orbital terms, the addition is viewed as taking place by interaction of the filled alkene it orbital with the empty p orbital on boron, accompanied by concerted C—H bond formation.158... 

Two trials employing D2 were carried out for this system. The results demonstrate the existence of an average kinetic isotopic effect, k/H2/k/D2 = 1.27. This suggests the involvement of C-H bond formation in the rate-determining step of the mechanism. 

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