The structure of propadienone (CH2CCO)

A complete r_o structure has been obtained for propadienone (CH₂CCCO) with the aid of ab initio molecular-orbital calculations. The effect of electron correlation has been investigated using third order Møller-Plesset perturbation theory. The molecule is found to be planar bent (CCC145°) and the calculated structure yields rotational constants which are in good agreemant with experimental values.     

Synthesis of 1,3,4,14b-tetrahydro-2H,10H-pyrazino[1,2-α]- pyrrolo[2,1-c][1,4]benzodiazepines

1,3,4,14b-Tetrahydro-2H,10H-pyrazino[1,2-α]pyrrolo[2,1-c] [1,4]benzodiazepines (1a-e) were synthesized to investigate their potential CNS activity. The key step in the synthesis was the formation of the 10,11-dihydro-5H-pyrrolo[2,1-c][1,4]benzodiazepine (13) by reduction and concomitant cyclization of the nitroketone (11). Biological evaluation of 1a-e revealed interesting properties for 1b (CGS 7525A) [2].     

An ab initio molecular orbital study of structures and energies of spirocompounds: spiro[3.3]heptane and spiro[3.3]hepta-1,5-diene

Ab initio molecular orbital theory with the STO-3G and 4-31G basis sets is used to determine the equilibrium geometries, enthalpies of formation, strain energies and spiro-interactions for spiro[3.3]heptane and spiro[3.3]hepta -1,5 - diene. For spiro[3.3]heptane, molecular mechanics calculations suggest that the component cyclobutane rings are puckered to a greater extent than in cyclobutane itself. For spiro[3.3]hepta - 1,5 - diene, STO-3G calculations predict that the component cyclobutene rings deviate slightly from an orthogonal arrangement. Spiro-interactions in spiro[3.3]hepta - 1,5 - diene are revealed by comparing the calculated structural parameters and strain energies with those of appropriate reference systems. The π-orbitals in spiro[3.3]hepta -1,5 -diene are predicted to be split by about 0.4 eV.     

A theoretical approach to substituent effects: Interaction between directly bonded groups in the isoelectronic series XNH3+, XCH3, and XBH3−

Ab initio molecular orbital theory including full geometry optimization at the 4-31G level is used to examine the interactions between substitutents X(X = Li, BeH, BH₂, CH₃, NH₂, OH and F) and substrates Y(Y = NH₃⁺, CH₃, BH₃^?) in the isoelectronic series XNH₃⁺, XCH₃ and XBH₃^?. The results indicate that the interaction energies are dominated by σ-effects. NH₃⁺ is found to interact favorably with the σ-donors (e.g. Li, BeH and BH₂) and unfavorably with the σ-acceptors (e.g. F, OH, NH₂). The reverse pattern a observed for XBH₃^?. The range of interaction energies for XCH₃ is considerably smaller than for XNH₃⁺ and XBH₃^?.     

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