Abstract
The electronic mechanism for the gas-phase 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne is studied through a combination of modern valence-bond theory in its spin-coupled (SC) form and intrinsic reaction coordinate calculations utilizing a complete-active-space self-consistent field wavefunction. Tt is shown that the concerted reaction follows a "heterolytic" route, during which three orbital pairs corresponding to three distinct bonds in the reactants (an in-plane pi bond in ethyne, and a C-N and an N-O in-plane bond in HCNO) shift simultaneously to create the two new bonds closing the isoxazole ring and a nitrogen lone pair. The analysis of the SC wavefunction strongly suggests that the reacting system remains nonaromatic throughout the most important part of the cycloaddition process. This investigation provides the first demonstration of an alternative SC description of a bond rearrangement, achieved through the movement of singlet orbital pairs through space, during which at least one of the orbitals within a pair becomes completely detached from the atomic centre with which it is associated initially and ends up localized about another centre.
| Original language | English |
|---|---|
| Pages (from-to) | 222-229 |
| Number of pages | 8 |
| Journal | THEORETICAL CHEMISTRY ACCOUNTS |
| Volume | 100 |
| Issue number | 1-4 |
| Publication status | Published - 1 Dec 1998 |
Keywords
- spin-coupled approach
- 1,3-dipolar cycloadditions
- reaction mechanisms
- valence-bond theory
- SPIN-COUPLED DESCRIPTION
- CASSCF WAVE-FUNCTIONS
- ELECTRONIC-STRUCTURE
- MC-SCF
- REPRESENTATIONS
- CYCLOADDITIONS
- OPTIMIZATION
- MOLECULES
- PATHWAYS