These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Accurate heats of formation of the "Arduengo-type" carbene and various adducts including H2 from ab initio molecular orbital theory.
    Author: Dixon DA, Arduengo AJ.
    Journal: J Phys Chem A; 2006 Feb 09; 110(5):1968-74. PubMed ID: 16451031.
    Abstract:
    The heats of formation of saturated and unsaturated diaminocarbenes (imadazol(in)-2-ylidenes) have been calculated by using high levels of ab initio electronic structure theory. The calculations were done at the coupled cluster level through noniterative triple excitations with augmented correlation consistent basis sets up through quadruple. In addition, four other corrections were applied to the frozen core atomization energies: (1) a zero point vibrational correction; (2) a core/valence correlation correction; (3) a scalar relativistic correction; (4) a first-order atomic spin-orbit correction. The value of DeltaHf( 298) for the unsaturated carbene 1 is calculated to be 56.4 kcal/mol. The value of DeltaHf( 298) for the unsaturated triplet carbene (3)1 is calculated to be 142.8 kcal/mol, giving a singlet-triplet splitting of 86.4 kcal/mol. Addition of a proton to 1 forms 3 with DeltaHf( 298)(3) = 171.6 kcal/mol with a proton affinity for 1 of 250.5 kcal/mol at 298 K. Addition of a hydrogen atom to 1 forms 4 with DeltaHf( 298)(4) = 72.7 kcal/mol and a C-H bond energy of 35.8 kcal/mol at 298 K. Addition of H- to 1 gives 5 with DeltaHf( 298)(5) = 81.2 kcal/mol and 5 is not stable with respect to loss of an electron to form 4. Addition of H2 to the carbene center forms 6 with DeltaHf( 298)(6) = 41.5 kcal/mol and a heat of hydrogenation at 298 K of -14.9 kcal/mol. The value of DeltaHf( 298) for the saturated carbene 7 (obtained by adding H2 to the C=C bond of 1) is 47.4 kcal/mol. Hydrogenation of 7 to form the fully saturated imidazolidine, 8, gives DeltaHf( 298)(8) = 14.8 kcal/mol and a heat of hydrogenation at 298 K of -32.6 kcal/mol. The estimated error bars for the calculated heats of formation are +/-1.0 kcal/mol.
    [Abstract] [Full Text] [Related] [New Search]