Ring opening of cyclopropylidene and internal rotation of allene
- Friedrich-Alexander Universitaet Erlangen (Germany)
- Univ. of Georgia, Athens, GA (United States)
Density functional theory and ab initio quantum mechanical techniques were employed to study the ring opening of singlet cyclopropylidene 1-S and the internal rotation of singlet allene 2-S. Single-point TZ2P energies were evaluated at CCSD(T) and multireference configuration interaction with single and double excitations (MR-CISD) levels. Employing the four most important configurations at the MR-CISD/TZ2P//UB3LYP/TZP level gave singlet-triplet separations for 1 of 11.1 kcal mol{sup -1} and for 2 48.9 kcal mol{sup -1}. Asymmetric transition structures for the ring opening of 1-S were obtained at B3LYP/TZP and CISD/TZP. The barriers are 4.2-4.5 kcal mol{sup -1} at CCSD(T)/TZ2P with these geometries. In contrast, only one C{sub s} symmetric TS was located at CASSCF-(4,4), and the ring opening barrier is only 3.6 and 3.1 kcal mol{sup -1} at CCSD(T)/TZ2P and MR-CISD/TZ2P, respectively. At CCSD(T)/6-31G* an asymmetric structure for the TS results confirming the predictions of the B3LYP and CISD methods. The B3LYP/6-31G* intrinsic reaction coordinate (IRC) delineated the complex modes of rotation of the methylene groups during the ring opening. The B3LYP/TZP ring opening (4.8 kcal mol{sup -1}) and allene internal rotation (44.6 kcal mol{sup -1}) barriers are in remarkably good agreement with the CCSD(T)/TZ2P//B3LYP/TZP value (4.5 kcal mol{sup -1}) on the barrier and with the MR-CISD/TZ2P//B3LYP/TZP barrier for the latter (44.6 kcal mol{sup -1}). 50 refs., 4 figs., 9 tabs.
- OSTI ID:
- 420877
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 40 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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