Torsional isomers in methylated aminoethanols - A jet-FT-IR study

Jet-FT-IR spectra of aminoethanol (AE), N-methylaminoethanol (MAE), and N,N-dimethylaminoethanol (DMAE) are presented and compared to gas-phase and matrix isolation IR, microwave, and quantum chemical data. The intramolecular O-H···N hydrogen bond gives rise to characteristically shifted O-H stretching bands and torsional difference bands in the monomer spectra. It stabilizes one out of 14 diastereomeric monomer conformations of AE and DMAE and two out of 27 diastereomeric MAE conformations. The latter two correspond to torsional or N-inversional isomers, the interconversion of which is hindered by the intramolecular hydrogen bond. Their energy difference is found to be <1.2 kJ/mol. The intermolecular aggregation patterns of the three aminoethanols are quite distinct and non-monotonic, as suggested by their O-H stretching fingerprints.Key words: aminoethanol, IR spectroscopy, conformation, hydrogen bond, supersonic jet.

Torsional Isomerism of Bent Metallocene Complexes The Molecular Structure of Bis(isopropylcyclopentadienyl)zirconiumdichloride in the Solid State

Bis(isopropylcyclopentadienyl)zirconiumdichloride (1) was synthesized by the reaction of isopropylcyclopentadienyl lithium with 1/2 molar equivalent of zirconiumtetrachloride and then crystallized from methylenechloride. Complex 1 crystallizes in space group C2/c with cell parameters a = 24.492(3)A, b = 13.525(1)Å, c = 22.894(3)Å, β = 117.90(1)°, Z = 16, R = 0.046, Rw = 0.057. There are three independent molecular entities of 1 in the asymmetric unit. These represent torsional isomers differing in the relative positions of the isopropyl substituents at the Cp-rings. The three torsional isomers may be described as anti-, syn-, and gauchelike metallocene rotamers.

Mikrowellenspektrum, interne Rotation, Struktur und Dipolmoment von Methylchloroform

The microwave spectrum of several symmetric and asymmetric top isotopic species of CH3CCl3 has been studied in the region from 8 to 40 GHz. A least squares analysis of the rotational con-stants gave the following structural parameters :dC-C =(1.541 ±0.001) A, dC-Cl = (1,7712 ± 0.0008) A, dC-H = (1.090 ± 0.002) A, ∢H—C—H= (110.04±0.25) ° , ∢Cl—C—Cl= (109.39 ±0.25) ° .A dipole moment of μ = (1.755 ± 0.015) D has been derived from the investigation of the Stark effect of the transition J=4→5 of CH3CCl3335. From intensity measurements the barrier to internal rotation is estimated to be (1740 ± 300) cal/mol. An analysis of the spectrum of CH2DCCl2Cl37 shows conclusively that methylchloroform in its equilibrium configuration has the methyl group staggered with respect to the CCl3-group. It could be shown that there exist two torsional isomers gauche and anti with specific microwave spectra.