Rotational spectra of the C13 isotopomers of the 2-aminoethanol monomer have been recorded in natural abundance using a Fourier-transform microwave spectrometer. The two sets of C13 isotopomer rotational constants were used to complete the 2-aminoethanol substitution structure. Rotational spectra of the van der Waals complexes 2-aminoethanol–water and 2-aminoethanol–argon were also recorded. Sixteen a-, b-, and c-type transitions were fit to the Watson A-reduction Hamiltonian for 2-aminoethanol–argon yielding A=4986.762(2) MHz, B=1330.693(3) MHz, and C=1143.933(3) MHz. Fifteen a- and b-type transitions for 2-aminoethanol–water were fit to A=4886.451(5) MHz, B=3356.038(2) MHz, and C=2311.715(2) MHz. The spectra are assigned to the lowest-energy ab initio [MP2/6-311++G(d,p)] structures of the two complexes. The conformation of 2-aminoethanol is unchanged in the argon complex, and the argon is 3.775 Å from the monomer center of mass. A network of intermolecular hydrogen bonds in the 2-aminoethanol–water complex replaces the intramolecular hydrogen bond of the monomer, and formation of the network requires the OCCN torsional angle to increase from 57° to 75° and the O–N distance to increase from 2.796 to 3.100 Å.
Rotational spectra have been recorded for five isotopic species of valinamide, the amide derivative of the amino acid valine. The rotational constants for the normal species are A ) 3019.242(1) MHz, B ) 1473.0587(7) MHz, and C ) 1252.5350(8) MHz. Ab initio calculations at the MP2/6-31G** level identified six conformational minima with three different orientations of the isopropyl side chain and two different intramolecular hydrogen bonding interactions. None of the theoretical structures reproduces the fifteen experimental moments of inertia derived from the rotational constants. Least-squares fits of the theoretical structure with χ 1 ) 300°and an amide-to-amine intramolecular hydrogen bond find that the amino amide backbone torsional angle Ψ increases from -9.3°to +9.7(30)°. The nitrogen atomic coordinates of the leastsquares-fit structure were found to be in agreement with the coordinates calculated using Kraitchman's equations for single isotopic substitution, but the nitrogen coordinates of the theoretical structures were significantly different from the Kraitchman coordinates.
The rotational spectra of nine isotopomers of the 3-hydroxytetrahydrofuran-water complex were recorded using a Fourier transform microwave spectrometer. The spectra are assigned to the networked structure of the complex, with intermolecular hydrogen bonds from the hydroxyl to the water oxygen and from water to the furanose-ring oxygen. Ab initio calculations, at the MP2/6-31G** level, indicate that this is the lowest energy structure of the complex, and it is based on the lowest-energy ring-puckering conformation of the 3-hydroxytetrahydrofuran monomer, C 4′ -endo. Stark effect measurements were used to determine the projections of the dipole moment on the principal inertial axes: µ a ) 1.2 (3) D, µ b ) 1.8 (2) D, µ c ) 0.7 (4) D, and µ tot ) 2.2 (2) D.
Two examples have been observed of an orthorhombic crystal type, composed of particles of dimensions about 10--6 to 10 -4 cm separated by water layers of the same order of magnitude. The particles themselves are small crystals, likewise of orthorhombic shape, at least to a first approximation. Like the cubic crystals of certain viruses and similar systems, they belong to the same type of phase as the smectic and nematic 'tactosols' and the amorphous 'coacervates'.In order to distinguish phases of this type from those composed of molecules in immediate contact, they might be named phases of higher order or superphases. Their equilibrium is mainly determined by the surface charges and their counterions. The influence of temperature is small. Such phases with translation periods (smectic or crystalline) exhibit iridescence instead of X-ray interference.The new orthorhombic crystals are obtained from the iridescent smectic tactosols of ferric chloride hydrolysate and of tungstic acid by a treatment that diminishes the distance between the particles. In the smectic state the crystal leaflets are distributed at random around the main axis. They reveal their orthorhombic oblong shape only at short distance in the supercrystals by arrangement in a threedimensional periodic lattice.
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