Trimethylenemethane

Abstract

I I 12 5 cp.s. 35 EPS.Figure 1. Proton nrnr spectra (60 Mcps) of 11, at various temperatures. The scale is in cycles per second downfield from tetramethylsilane. 0"'""'" n iiswr. 5 5 cps.Figure 3. Proton nmr spectra (60 Mcps) of IV at various ternperatures. The scale is in cycles per second downfield from tetramethylsilane. 120 cp 5. 30 CRS Figure 2. Proton nmr spectra (60 Mcps) of I11 at various temperatures. The scale is in cycles per second downfield from tetramethylsilane.the others are then "axial." The eight "equatorial" bonds are shown in V. The pseudo-rotation or wagging process mentioned above results in the formation of two sets of bonds: let set A be [le, 2e, 3e, 4a, 5a, 6a, 7e, 8e]; then set B is [la, 2a, 3a, 4e, 5e, 6e, 7a, 8a]. Only ring inversion will mix set A with set B. A large group can be accommodated in set A (positions le, 2e, 3e, 7e, or 8e) or in set B (positions 4e, 5e, or 6e). Therefore, the low-temperature nmr spectrum of an alkylcyclooctane should show two conformational isomers, even if the sole ring conformation is the boat-chair. Also it is possible to have two equatorial substituents on adjacent carbon atoms in either set A or set B, and therefore trans fusion to another ring also allows two conformational isomers to be present. It can also be seen that conversion of a group from set A to set B and vice versa is analogous to ring inversion in cyclooctane itself, except that it should lead, at high temperatures, to a relatively narrow band for the methylene protons instead of a single sharp line as with cycl~octane.~ Thus, the present evidence points to the boat-chair as the major conformation in cyclooctane and monosubstituted cyclooctanes. The assignment* of con-(7) A mechanism for inversion which is satisfactory for 11, 111, and IV, as well as for cyclooctane itself, involves stretching out CS and C7 in V to give a centrdymmetrical ring "conformation" (conformation V in ref Sa) as a transition state. (8) N. L. Allinger and S. Greenberg, J. Am. Chem. SOC., 84, 2394 ( 1962).figurations to the 5-i-butylcyclooctanols, made on the basis of a crown conformation, is therefore not convincing, but it is not easy to predict the relative proportions of boat-chair and crown forms for these compounds. Further work on the conformations of eightmembered rings is in progress. Trimethylenemethane Sir :Trimethylenemethane (I) is important in theoretical chemistry by virtue of the fact that the central carbon I atom of this molecule attains the maximum T bond order possible for any carbon at0m.l The magnitude of the bond order thus obtained (4.732) is the base for numerous calculations of free valence indexes of carbon compounds. In addition, this molecule has been used as a model in theoretical calculations of negative spin density in triplet states2 and in a comparison of different methods useful in theoretical calculations of the energies of T systems.(1) (a) W. E. Moffitt, footnote to C.

The synergy between qualitative theory, quantitative calculations, and direct experiments in understanding, calculating, and measuring the energy differences between the lowest singlet and triplet states of organic diradicals

“…1, 2 Moreover, in order to minimize Coulombic repulsion between the open-shell electrons in the singlet states of both diradicals, the singlets can be predicted to utilize different sets of NBMOs than the triplet states. EPR studies have established that both TMM [80][81][82][83] and MBQDM 84 do, in fact, both have triplet ground states. As described in the following sections, NIPES subsequently provided accurate values for E ST in each of these diradicals and also in oxyallyl, a heteroatom derivative of TMM.…”

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

“…Here the adiabatic S-T gaps for methylene, halocarbenes (CF 2 , CCl 2 , and CBr 2 ), and TMM calculated with the CAS-BCCC4 method are listed in Table 6 1 and 1 B 1 ) are predicted to be of C 2v symmetry (not degenerate, due to the Jahn -Teller effect) [31,171,172]. In our CAS-BCCC4 calculations, the equilibrium structures in the ground-and lowest-excited states are from FCI/TZ2P optimizations [173] for CH 2 , from CASSCF(18,12)/cc-pVTZ optimizations [174] for halocarbenes, and from SF-DFT/6-31G(d) optimizations [31] for TMM.…”

Didehydro radical anions from ketones via O− chemical ionization

“…Diradicals, an atom or molecule in which two electrons occupy two degenerate or nearly degenerate molecular orbitals [1], have been of great interest for a long time [2,3]. One intriguing property of a diradical is the energy difference between its singlet and triplet states.…”