卡宾重排无与伦比：C(7)H(6)势能面细节得以揭示。

Carbene Rearrangements Unsurpassed: Details of the C(7)H(6) Potential Energy Surface Revealed.

作者信息

Schreiner Peter R., Karney William L., von Ragué Schleyer Paul, Borden Weston Thatcher, Hamilton Tracy P., Schaefer III Henry F.

机构信息

Computer Chemistry Center, Institut für Organische Chemie der Universität Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany, the Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, the Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700, and the Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294.

出版信息

J Org Chem. 1996 Oct 4;61(20):7030-7039. doi: 10.1021/jo960884y.

DOI:10.1021/jo960884y

PMID:11667604

Abstract

The rearrangement of phenylcarbene (1) to 1,2,4,6-cycloheptatetraene (3) has been studied theoretically, using SCF, CASSCF, CASPT2N, DFT (B3LYP), CISD, CCSD, and CCSD(T) methods in conjunction with the 6-31G, 6-311+G, 6-311G(2d,p), cc-pVDZ, and DZd basis sets. Stationary points were characterized by vibrational frequency analyses at CASSCF(8,8)/6-31G and B3LYP/6-31G. Phenylcarbene (1) has a triplet ground state ((3)A") with a singlet-triplet separation (DeltaE(ST)) of 3-5 kcal mol(-)(1). In agreement with experiment, chiral 3 is the lowest lying structure on this part of the C(7)H(6) potential energy surface. Bicyclo[4.1.0]hepta-2,4,6-triene (2) is an intermediate in the rearrangement of 1 into 3, but it is unlikely to be observable experimentally due to a barrier height of only 1-2 kcal mol(-)(1). The enantiomers of 3 interconvert via the (1)A(2) state of cycloheptatrienylidene (4) with an activation energy of 20 kcal mol(-)(1). The "aromatic" (1)A(1) state, previously believed to be the lowest singlet state of 4, is roughly 10 kcal mol(-)(1) higher in energy than the (1)A(2) state, and, in violation of Hund's rule, (3)A(2) is also calculated to lie above (1)A(2) in energy. Thus, even if (3)A(2) were populated, it is likely to undergo rapid intersystem crossing to (1)A(2). We suggest (3)B(1)-4 is the metastable triplet observed by EPR.

摘要

已使用SCF、CASSCF、CASPT2N、DFT（B3LYP）、CISD、CCSD和CCSD（T）方法，并结合6-31G、6-311+G、6-311G（2d，p）、cc-pVDZ和DZd基组，从理论上研究了苯卡宾（1）重排为1,2,4,6-环庚四烯（3）的过程。通过在CASSCF(8,8)/6-31G和B3LYP/6-31G水平上进行振动频率分析对驻点进行了表征。苯卡宾（1）具有三重态基态（(3)A"），单重态-三重态分裂（ΔE(ST)）为3 - 5 kcal mol(-)(1)。与实验结果一致，手性3是C(7)H(6)势能面上这一部分能量最低的结构。双环[4.1.0]庚-2,4,6-三烯（2）是1重排为3过程中的中间体，但由于其势垒高度仅为1 - 2 kcal mol(-)(1)，因此不太可能通过实验观测到。3的对映体通过环庚三烯叉（4）的(1)A(2)态相互转化，活化能为20 kcal mol(-)(1)。先前认为是4的最低单重态的“芳香性”(1)A(1)态，其能量比(1)A(2)态大约高10 kcal mol(-)(1)，并且违反洪德规则，计算表明(3)A(2)的能量也高于(1)A(2)。因此，即使(3)A(2)被占据，它也可能迅速发生系间窜越至(1)A(2)。我们认为(3)B(1)-4是通过电子顺磁共振观测到的亚稳三重态。