CCC Plane Research Articles

ChemInform Abstract: CNDO 2 DIFFERENCE ELECTRON DENSITY CONTOURS IN SATURATED THREE‐MEMBERED RINGS

Theoretical difference electron density contours in the NCC, CCC, and OCC ring planes of ethyleneimine quinone, cis-1,2,3-tricyanocyclopropane and tetracyanoethylene oxide molecules, respectively, were calculated by the CNDO/2 molecular orbital method. They are qualitatively in good agreement with the experimental contours, and have reproduced the most characteristic features of the observed electron distributions in the bent bonds in the three-membered rings. The theoretical difference contours in the three-membered ring planes of aziridine, cyclopropane and oxirane molecules have shown essentially the same bonding electron distributions as the corresponding contours in the more complex molecules mentioned above.

CNDO/2 Difference Electron Density Contours in Saturated Three-membered Rings

Abstract Theoretical difference electron density contours in the NCC, CCC, and OCC ring planes of ethyleneimine quinone, cis-1,2,3-tricyanocyclopropane and tetracyanoethylene oxide molecules, respectively, were calculated by the CNDO/2 molecular orbital method. They are qualitatively in good agreement with the experimental contours, and have reproduced the most characteristic features of the observed electron distributions in the bent bonds in the three-membered rings. The theoretical difference contours in the three-membered ring planes of aziridine, cyclopropane and oxirane molecules have shown essentially the same bonding electron distributions as the corresponding contours in the more complex molecules mentioned above.

Conformational study of π-tetracarbonyl(mono-olefin)iron complexes by infrared spectra and dipole moment measurements

The electric dipole moments of the complexes π-LFe(CO)4, where L =trans-PhCHCHCOCH3, trans-PhCHCHCOPh, trans-PhCHCHCHO, CH2HCHO, and CH2CHCN, have been determined. It is found that the ligand plane is never parallel to the axis of the trigonal bipyramid. The ligand CO group in the carbonyl derivatives is slightly out of the CCC plane. The structure of the acrylonitrile complex in solution is the same as that found for the solid from X-ray studies. The ketone iigands have the same conformation in the complex as in the free ligand. The aldehyde ligands. present only as the s-trans-conformer in the free state, form both isomers when bonded to the metal. The enthalpy variation for the conformational equilibrium s-cis⇄s-trans for the aldehyde complexes has been ca culated from i.r. data, and an assignment of the CO stretchings has been proposed.

ChemInform Abstract: MICROWAVE SPECTRUM, DIPOLE MOMENT AND STRUCTURE OF ISOPROPYL CYANIDE

Abstract The microwave spectrum of isopropyl cyanide, (CH 3 ) 2 CHCN, has been recorded from 26.5 to 40.0 GHz. Both A- and C-type transitions were observed. The R-branch assignments have been made for the ground and three different excited states. The following structural parameters were obtained: r (C-CN) = 1.501 A, ∠CCC = 113.8°, and an angle between the CCC plane and the CN bond of 53.8° with reasonable assumptions made for the structural parameters for the isopropyl moiety and the nitrile bond. The dipole moment components were determined to be μ a = 4.05±0.02, μ c = 1.4 ± 0.2 and μ t = 4.29 ±0.10 D. The dipole moment of t-butyl cyanide has been re-measured and found to have a value of4.34±0.04 D. From the relative intensities of the excited state lines, the two torsional modes were found to have frequencies of 200 ±20 and 249 ±10 cm −1 which gave a periodic barrier to internal rotation of 3.3 kcal mole −1 .

Microwave spectrum, dipole moment and structure of isopropyl cyanide

The microwave spectrum of isopropyl cyanide, (CH 3) 2CHCN, has been recorded from 26.5 to 40.0 GHz. Both A- and C-type transitions were observed. The R-branch assignments have been made for the ground and three different excited states. The following structural parameters were obtained: r(C-CN) = 1.501 Å, ∠CCC = 113.8°, and an angle between the CCC plane and the CN bond of 53.8° with reasonable assumptions made for the structural parameters for the isopropyl moiety and the nitrile bond. The dipole moment components were determined to be μ a = 4.05±0.02, μ c= 1.4 ± 0.2 and μ t = 4.29 ±0.10 D. The dipole moment of t-butyl cyanide has been re-measured and found to have a value of4.34±0.04 D. From the relative intensities of the excited state lines, the two torsional modes were found to have frequencies of 200 ±20 and 249 ±10 cm −1 which gave a periodic barrier to internal rotation of 3.3 kcal mole −1.

The question of an open-ring form of cyclopropanone

The semi-empirical lcao-mo-scf theory has been applied to both the closed-ring and open-ring structures of cyclopropanone. Three main geometrical configurations have been considered, namely the (0,0), (0,90), and (90,90) forms, with the numbers in parentheses referring to the angles between the planes of the CH 2 group and the CCC plane. The ground state of the compound is found to be the (90,90) form, with a small value (62.5°) of the unique CCC angle. Thus the compound is best described as a closed-ring ketone, in agreement with recent experimental data. The open-ring form, which is found to be quite high in energy by these calculations, should probably not be considered as a major intermediate in the cycloaddition reactions of the compound. The interconversion of the two forms through a disrotatory motion involves a barrier, which occurs around the (30,30) form. Protonated cyclopropanone is also predicted to resist opening, as is the lowest triplet state of the compound ( 3 A 2), which loosely corresponds to an n → π * transition.

Crystal structure of malonamide

Crystals of malonamide, CH2(CONH2)2, are monoclinic, space group P21/c, a= 13·07, b= 9·45, c= 8·04 A, β= 73·0°, Z= 8 (two molecules in the asymmetric unit). The structure was determined with Mo-Kα diffractometer data by the symbolic addition procedure, and refined by least-squares methods, to R 0·05 for 941 observed reflexions. Hydrogen atom positions were determined.The two symmetry-unrelated molecules have different orientations in the crystal, but have similar conformations and dimensions. The amide groups are rotated out of the central CCC plane, one group in each molecule by about 65°, and the other group by 40°. The mean bond distances, after applying rotational oscillation corrections, are C–C 1·507, C–N 1·334, C–O 1·253 A(σ 0·004 A); there are no significant deviations from these mean values. The molecules are held together by a system of eight N–H ⋯ O hydrogen bonds (2·89–3·14 A) involving all the amino-hydrogen atoms, with each oxygen atom acting as an acceptor in two hydrogen bonds.

Microwave Spectrum, Rotational Isomerism, and Internal Barrier Functions in Propionyl Fluoride

The microwave spectrum of propionyl fluoride [CH3CH2COF] proves the existence of two stable rotameric conformations. For the cis form (methyl eclipsing oxygen) with a planar heavy-atom skeleton, rotational constants A = 10 042.53, B = 3762.19, C = 2832.69 MHz and a dipole moment of μtotal = 2.90, μa = 2.22, μb = 1.87 D have been determined. An approximate structure has been fitted to these data. Eight satellite spectra of the cis form have been analyzed yielding a torsional vibration frequency around the central carbon–carbon bond of 85 ± 3 cm−1 and an apparent barrier height V3 = 2400 ± 60 cal/mole hindering the internal rotation of the methyl group. The gauche conformation has rotational constants A = 8701.9, B = 3976.9, C = 3108.7 MHz and a total dipole moment of μtotal = 3.09 D with components μa = 2.93, μb = 0.32, and μc = 0.91 D. The dihedral angle between the CCC and COF plane is found to be 120° ± 2° and the torsional vibration frequency of the gauche form around the central carbon–carbon bond is 54 ± 5 cm−1. Energetically, the cis form is favored over the gauche form by 1290 ± 50 cal/mole. The data obtained on the two rotamers are used to derive the potential-energy function V(υ) for rotation around the central C–C bond. The first four Fourier coefficients are found to be V1 = 930, V2 = 720, V3 = 1150, and V4 = 130 cal/mole, resulting in a potential barrier of 2100 cal/mole separating the cis from the gauche form and 800 cal/mole separating the two equivalent gauche forms from each other. The modification of the υ-dependent intramolecular forces which accompanies the substitution of one hydrogen atom by a methyl group is obtained. With the assumption that these modifications are additive and from the observed approximate constancy of V3, it becomes possible to predict the potential functions of several related molecules, for later comparison with experiment.