Hydroxymethylene has never actually been observed, although it is believed to be an intermediate both in the photo-fragmentation of formaldehyde to hydrogen and carbon monoxide,

and in the photo-dimerization of formaldehyde in an argon matrix:

Does hydroxymethylene actually exist? To have a chance €œat life,€ it must be separated from both its rearrangement product (formaldehyde) and from its dissociation product (hydrogen and carbon monoxide) by a sizable energy barrier (>80 kJ/mol). Of course, it must also actually be a minimum on the potential energy surface.

a. First calculate the energy difference between formaldehyde and hydroxymethylene and compare your result to the indirect experimental estimate of 230 kJ/mol. Try two different models, B3LYP/6-31G* and MP2/6-31G*. Following calculation of the equilibrium geometry for hydroxymethylene, obtain vibrational frequencies. Is hydroxymethylene an energy minimum? How do you know? Is the energy difference inferred from experiment reasonably well reproduced with one or both of the two models?

b. Proceed with the model that gives the better energy difference and try to locate transition states both for isomerization of hydroxymethylene to formaldehyde and for dissociation to hydrogen and carbon monoxide. Be certain to calculate vibrational frequencies for the two transition states. On the basis of transition states you have located, would you expect that both isomerization and dissociation reactions are available to hydroxymethylene? Explain. Do both suggest that hydroxymethylene is in a deep enough energy well to actually be observed?

Transcribed Image Text:

Н.со_ нсон]—н, +со |Н,со- -нсон). н.со —носн,сно