Hydroxycarbene isomer

These values suggest that the two hydroxycarbene isomers convert into one another very easily. The barrier to molecular dissociation of the cis form is significant, however, and so this structure probably does not dissociate directly, but rather first converts to the trans isomer, which is subsequently transformed into formaldehyde, which dissociates to carbon monoxide and hydrogen gas. The article from which this study was drawn computes the activation energy for the trans to cis reaction as 28.6 kcal- moT at RMP4(SDQ)/6-31G(d,p) (it does not consider the other reactions). 

The hydroxycarbene isomer (H)Co(CO)3(CHOH) was also examined. It yielded a complex with molecular electronic energy more than 60 kcal/mole higher on the energy scale. The hydroxycarbene complex is not likely to play a significant role in the catalytic cycle. It is of some interest to inquire why the 18e hydroxycarbene complex (H)(CO) Co(=CH0H) is less stable than the 16e isomer (H)(CO)3C0(CH2O). The results suggest that the formation of the carbonyl double bond makes the critical difference. The electronically delocalized structure (H)(CO)3Co+5-CH2 0" may provide some extra stabilization for the formally unbonded formaldehyde moiety. The resonance form is dipolar and could be further stabilized by polar solvents. 

We can easily identify both structures by the value of the dihedral angle. In the one on the left, the dihedral angle has increased to 118.3°, indicating that this side of the path is leading to the trans form. Indeed, if we look at ail of the points in the reaction path, we see that the dihedral angle steadily increases on this side of the transition structure, and steadily decreases on the opposite side. From the latter, we can conclude that the right structure is tending toward the cis form. Thus, we have confirmed that this transition structure does in fact connect the cis and trans isomers of hydroxycarbene. 

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