Toward the Observation of the Tin and Lead Analogs of Formaldehyde.

Heavy aldehyde and ketone analogues, R2X═O (X = Si, Ge, Sn, or Pb), differ from their R2C═O counterparts due to their greater tendency to oligeramize as the X═O bond polarity increases as one goes down the periodic table. To date, H2Sn═O and H2Pb═O have eluded experimental detection. Herein we present the most rigorous theoretical study to date on these structures, providing CCSD(T)/pwCVTZ fundamental frequencies computed on CCSD(T)/CBS optimized structures for the H2X═O (X = Sn, Pb) potential energy surface. The focal point approach is employed to produce the CCSDTQ/CBS relative energies. For the Sn and Pb structures, the carbene-like cis-HXOH was the global minima, with the trans species being less than 0.6 and 1.1 kcal mol-1 above the cis structures, respectively. The formaldehyde-like H2X═O structure is in an energy well of at least 34.8 and 25.4 kcal mol-1 for Sn and Pb, respectively. Our results provide guidance for future work that may detect H2Sn═O or H2Pb═O for the first time.