Cornelia Mlynek

Resolution of chiral [2.2]paracyclophanes by enantioselective gas chromatography

Abstract [2.2]Paracyclophanes possessing a substituent on the aromatic ring are dissymmetric compounds due to the restricted rotation of the benzene rings. For interconversion of enantiomers temperatures above 200 °C are necessary. We have succeeded in resolving the enantiomers of some mono-substituted [2.2]paracyclophanes by enantioselective gas chromatography using 2,3-di-O-methylated β-cyclodextrins with bulky O-(1,1,2-trimethylpropyl)-dimethylsilyl or O- t .butyl-dimethylsilyl substituents in the 6-position of the glucose units as chiral stationary phases.

Intramolecular π-Type Hydrogen Bonding and Conformations of 3-Cyclopenten-1-ol. 2. Infrared and Raman Spectral Studies at High Temperatures

The vapor-phase infrared and Raman spectra of 3-cyclopenten-1-ol (3CPOL) have been collected at temperatures ranging from 25 to 267 degrees C. These clearly show the presence of four conformations of 3CPOL with the one with intramolecular pi-type hydrogen bonding being most abundant. The spectra of all four conformations have been assigned, and these agree well with the computed values from the DFT calculation. The frequency shifts observed for the different conformations are in accord with the predicted values. In the O-H stretching region the conformer A with the pi-type intramolecular hydrogen bond has the lowest stretching frequency at 3623.4 cm(-1) while the three higher energy conformers have frequencies 14.2, 32.0, and 36 cm(-1) higher. In the C=C stretching region conformer A again has the lowest frequency at 1607.3 cm(-1) while the other conformers have bands 2.1, 8.0, and 13.4 cm(-1) lower. Both the O-H stretching and the C=C stretching force constants are decreased about 2% by the hydrogen bonding. Five of the other vibrations show significant predicted frequency shifts up to 193 cm(-1). Analysis of intensity data at different temperatures was used to calculate the energy difference between the two most stable conformers. This was found to be 435 +/- 160 cm(-1), and the result agrees reasonably well with the high level ab initio results which range from 274 to 401 cm(-1).

A General Route to Fully Terminally tert‐Butylated Linear Polyenes

Starting from the readily available α,β-unsaturated ketone, 3-tert-butyl-4,4-dimethyl-2-pentenal, higher vinylogues, and fully terminally tert-butylated polyolefins with up to 13 consecutive conjugated double bonds have been prepared by either McMurry dimerization or Wittig chain-elongation routes. The highly unsaturated conjugated π systems, which show a remarkable stability, have been characterized by spectroscopic methods and, in many cases, by X-ray structural analysis. The yields are high enough to allow for thorough chemical reactivity studies.

On the trimerization of cyanoacetylene: mechanism of formation of tricyanobenzene isomers and laboratory detection of their radio spectra.

In support of a deeper understanding of the chemistry of cyanoacetylene--a known constituent of planetary atmospheres and interstellar space--theoretical and experimental studies address the chemical mechanism of dimerization and trimerization, and provide high-resolution rotational spectra of two of the trimeric products, 1,2,3- and 1,2,4-tricyanobenzene. Analysis of the rotational spectra is particularly challenging because of quadrupolar coupling from three (14)N nuclei. The laboratory rotational spectra provide the basis for future searches for these polar aromatic compounds in interstellar space by radio astronomy.

Intramolecular OH/π interaction: the molecular structure and conformations of 3-hexyn-1,6-diol

Abstract The molecular structure and conformational composition of 3-hexyn-1,6-diol have been studied by the gas electron diffraction method and by ab initio calculations. Four conformers ( AA , G + G −, G + G + and GA ) have been taken into account. The experimental data are in accordance with a conformational mixture consisting of 62.2% GG (equal parts of G + G − and G + G +) and 37.8% GA with a standard deviation of 10.3%. Similar results were, however, obtained when a small contribution (0≤ x ≥12%) from the high energy AA conformer was introduced and the other forms were properly corrected ( GG (62.2+ x %); GA (37.8−2 x %)). From the experimental data the total amount of gauche contribution in the two parts of the molecule is accordingly estimated to be in the region 76.0–86.3%. The GG and GA conformers are characterized by the formation of two, respectively one, OH⋯π hydrogen bonds.

The IR, Raman and NMR spectra and conformations of cyclohexylallene

Abstract Three conformers of cyclohexylallene, designated I, II and III, were observed in the IR and Raman spectra. Metastable crystals formed by annealing an amorphous solid from 80 K to 140 K, and crystals formed under a pressure of 30 kbar at ambient temperature, contained conformer II. The stable crystals obtained after heating the metastable crystals to 195 K contained conformer I. The conformer III was observed as a minor component in a nitrogen matrix heated to 900 K before deposition. Negligible intensity variations between the bands of conformer I and II were observed with nozzle temperatures 300–900 K in the argon and nitrogen matrices, indicating a ΔHo(I-II) below 0.4 kJ mol−1 while ΔHo(III-II) was equal to 6.5 kJ mol−1 and a barrier higher than ca. 11 kJ mol−1 was observed between the latter. Variable temperature measurements in Raman indicate ΔHo(I-II) ≈ 0.9 kJ mol−1 in the liquid. The 13C NMR spectra show that in deuteromethanol solution the equatorial conformer dominates (≈ 2% a at 193 K, ΔGo(a–e) ≈ 6.4 kJ mol−1). Analysing the temperature dependence of the vicinal H-H coupling across the cyclohexane - allene carbon bond on the basis of a guache ↔ anti equilibrium it is found 40% anti and 60% gauche in methanol solution at ambient temperature. We conclude that the abundant conformers II and I being respectively the anti and the gauche conformer, while III is the anti axial conformer.

Weak C—H...N[triple‐bond]C hydrogen bonds in the structures of two poly(cyano)‐substituted ring systems

In benzene-1,2,3-tricarbonitrile, C9H3N3, the packing of the two independent molecules is three-dimensional and complex, involving inter alia bifurcated (C-H)2...N systems from neighbouring CH groups. In [2.2]paracyclophane-4,5,12,13-tetracarbonitrile, C20H12N4, the [2.2]paracyclophane systems display the usual distortions, namely lengthened C-C bonds and widened sp3 angles in the bridges, narrow angles in the six-membered rings at the bridgehead atoms, and flattened boat conformations of the rings. The molecules are linked by a series of C-H...N interactions to form layers parallel to the ab plane.

(5RS,6RS)-5,6-Di-tert-butyl-2,2,9,9-tetramethyldecane-3,8-dione

The title compound, C22H42O2, displays approximate twofold symmetry. The elongated central single bond [1.563u2005(3)u2005A] and widened angles [116.00u2005(16) and 115.80u2005(16)°] at the methylxadene C atoms are probably indicators of steric strain. Molxadecules are linked in inversion-symmetric pairs by a bifurcated weak hydrogen-bond system of the form (C—H)2⋯O.

(E)-2,2,6,6-Tetra­methyl­hept-4-en-3-one

The title compound, C11H20O, shows a wide Me3C—C=C angle of 129.60u2005(14)°. Molxadecules associate into zigzag chains parallel to [101] via a hydrogen bond Hmethxadyl⋯Oketone.