A theoretical study of low-lying electronic states of aminonitrene, phosphinonitrene, and phosphinocarbene

Abstract

A theoretical study of the electronic structure and spectroscopic properties of the low-lying electronic states of the molecule SiB A theoretical investigation of some lowlying electronic states of imidazoleThe recently formulated multiconfiguration-based unitary coupled electron pair approximation (UCEPA) is compared with muItireference configuration interaction (MR-CISD) calculations, including all single and double excitations, for the molecules in this study. The electronic states of the molecules in this study are not only of experimental interest, but represent a challenge to any formalism to accurately predict the energy separations of the lowlying electronic states. The equilibrium geometries and fundamental vibrational frequencies of the three lowest electronic states (i.e., IA I , 3A If, and IA ") of amino nit rene H 2 N 2 , and phosphinonitrene, H 2 PN, have been determined using a split-valence basis with polarization functions on the heavy atoms and a small complete active space self-consistent-field (CASSCF) description of the active space. Both MR-CISD and UCEPA calculations have been performed at the equilibrium structures using larger basis sets to accurately determine the relative energetics of the electronic states. The equilibrium geometries and vibrational frequencies of the two lowest electronic states (Le., I A ' and 3 A ") of phosphinocarbene, H 2 PCH, have been determined using a larger than double zeta basis set, augmented with polarization and diffuse functions, and a CASSCF description of the active space. Both MR-CISD and UCEPA calculations were performed on the equilibrium structures and predict that the singlet lies between 10.4 and 11.8 kcallmollower in energy than the triplet. The use of a generalized valence bond (GVB) reference function within UCEPA is introduced and is shown to be a useful approximation.

Thermochemistry, Tautomerism, and Thermal Decomposition of 1,5-Diaminotetrazole: A High-Level ab Initio Study

“…This reaction yields three products, viz., N 2 , cyanamide, and 1,1-diazine (Figure ). Note that such process is very specific for DAT in comparison with other 1-substituted tetrazoles due to enhanced stabilization of 1,1-diazine, which is a singlet aminonitrene, in comparison with similar simple singlet nitrenes (e.g., :NH or :N–CH 3 ). , …”

“…Note that such process is very specific for DAT in comparison with other 1substituted tetrazoles due to enhanced stabilization of 1,1diazine, which is a singlet aminonitrene, in comparison with similar simple singlet nitrenes (e.g., :NH or :N−CH 3 ). 52,53 The elimination of azide NH 2 N 3 (TS3, Figure 4, left side) is ∼10 kcal mol −1 higher than the primary channel (Scheme 4). Although the former reaction has been scrutinized in detail in a recent computational work, 29 it turned out to be entirely unimportant kinetically.…”

How Is a Metabolic Intermediate Formed in the Mechanism‐Based Inactivation of Cytochrome P450 by Using 1,1‐Dimethylhydrazine: Hydrogen Abstraction or Nitrogen Oxidation?

“…This finding is consistent with the trend observed in previous ab initio studies. [31] It was previously postulated that Int1A may also undergo a rebound to form a N-hydroxyl intermediate (Intermediate 2 in Scheme 1). [22] However, our attempts to identify the pathway connecting Int1A and In- termediate 2 were unsuccessful, and we found that a N-hydroxyl intermediate was obtained only on Path B (Int2B).…”

Stable Carbenes

“…Similar conclusions can be drawn from the X-ray crystal structure analysis of the phosphinosilylcarbene XIg (Figure 12), 82 the silyl group playing the same role as the phosphonio group of XIIa. The Si2N2C3N1C2P1C1Si1 skeleton is planar (maximum The first study by Hegarty and co-workers 84 concluded that the parent phosphinocarbene H 2 PCH XIg* has a singlet ground state, with a singlettriplet gap of 3 kcal/mol, while later on Hoffmann and Kuhler 85 predicted a somewhat larger gap (6.7 kcal/ mol) using a more sophisticated level of theory. Together, the planar geometry of the singlet state and the shortness of the PC bond (1.616 Å) confirm the strong interaction of the phosphorus lone pair with the vacant orbital of the carbene center.…”

“…The first study by Hegarty and co-workers concluded that the parent phosphinocarbene H 2 PCH XIg* has a singlet ground state, with a singlet−triplet gap of 3 kcal/mol, while later on Hoffmann and Kuhler predicted a somewhat larger gap (6.7 kcal/mol) using a more sophisticated level of theory. Together, the planar geometry of the singlet state and the shortness of the PC bond (1.616 Å) confirm the strong interaction of the phosphorus lone pair with the vacant orbital of the carbene center.…”