Effect of fluorination: gas-phase structures of N,N-dimethylvinylamine and perfluoro-N,N-dimethylvinylamine.

The gas-phase structures of N,N-dimethylvinylamine, (CH(3))(2)NC(H)=CH(2) (1), and perfluoro-N,N-dimethylvinylamine, (CF(3))(2)NC(F)=CF(2) (2), were determined by gas electron diffraction and quantum chemical methods (B3LYP and MP2 with 6-31G basis sets). The configuration around nitrogen is slightly pyramidal in both compounds, with the sum of the nitrogen bond angles 351.2(12) degrees and 354.8(6) degrees in 1 and 2, respectively. In the parent compound 1, the (CH(3))(2)N group lies nearly in the plane of the vinyl group, and the nitrogen lone pair (lp) is almost perpendicular to this plane (Phi(C=C-N-lp) = 98(6) degrees). In the perfluorinated species 2, however, the (CF(3))(2)N group is oriented perpendicular to the vinyl plane, and the lone pair is parallel to the C=C bond (Phi(C=C-N-lp) = 2(5) degrees). A natural bond orbital analysis provides a qualitative explanation for this conformational change upon fluorination. The sterically unfavorable in-plane orientation of the dimethylamino group in 1 is stabilized by conjugation between the nitrogen lone pair and the C=C pi-bond. The anomeric effect between the lone pair and the C(alpha)-F sigma-bond in addition to steric effects favors the perpendicular orientation of the (CF(3))(2)N group in 2. Both quantum chemical methods reproduce the experimental structures satisfactorily.

Structures and conformations of trifluoromethyl fluoroformate and perfluorodimethyl carbonate.

The conformational properties and geometric structures of trifluoromethyl fluoroformate, CF(3)OC(O)F (1), and perfluorodimethyl carbonate, (CF(3)O)(2)CO (2), have been studied by matrix IR spectroscopy, gas electron diffraction (GED), and quantum chemical calculations (MP2 and B3LYP with 6-311G basis sets). In both compounds the synperiplanar orientation of the O-CF(3) groups relative to the C=O double bond is preferred. If heated Ar/1 and Ar/2 mixtures are deposited as a matrix at 14 K, new bands appear in the matrix IR spectra which are assigned to the anti form of 1 and to the syn/anti form of 2. At room temperature the contribution of the anti rotamer of 1 is 4% (DeltaH degrees = H degrees (anti) - H degrees (syn) = 1.97(5) kcal/mol), and the contribution of the syn/anti conformer of 2 is estimated to be less than 1%. These high-energy conformers are not observed in the GED experiment. The quantum chemical calculations reproduce the structural and conformational properties of both compounds satisfactorily.

((Fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3: unexpected conformational properties.

The geometric structure and conformational properties of ((fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3, are investigated by gas electron diffraction (GED) experiments, IR (gas) spectroscopy, and quantum chemical calculations (HF, MP2, and B3LYP with 6-31G* basis sets). The GED intensities are reproduced best with a mixture of 79(12)% trans-syn and 21(12)% cis-syn conformers. "Trans/cis" describes the orientation around the S=N double bond (FC(O) group relative to sulfur substituents), and "syn" refers to the orientation of the C=O bond relative to the S=N bond. From the intensities of the C=O bands in the IR (gas) spectrum, a composition of 86(8)%:14(8)% is derived. These ratios correspond to delta G0(GED) = 0.79(36) and delta G0(IR) = 1.09(35) kcal mol-1. The preference of a trans structure, around the S=N double bond is unexpected, since all imidosulfur compounds studied thus far possess a cis configuration. The conformational properties are reproduced qualitatively correctly by all theoretical calculations. The predicted energy differences delta E(HF) = 2.41, delta E(MP2) = 0.64, and delta E(B3LYP) = 0.28 kcal mol-1 are larger or slightly smaller than the experimental values. Additional theoretical calculations (B3LYP) for several imidosulfur compounds reveal that only FC(O)N=S(F)CF3, with mixed substitution at sulfur and the FC(O) group bonded to nitrogen, prefers the trans structure.

[Microbial contamination of tube feeding solutions]. / Mikrobiel kontamination af sondekost.

Forty patients receiving respirator treatment were subdivided at random to receive tube-feeding with either a "home-made" powder product (group 1) or a ready-made sterile standard tube-feeding product: Salvimulsin MCT (group 2). Tube-feeding was administered as a continuous drip infusion and the patients were followed throughout three days, with particular attention to the development of diarrhoea. A series of cultures were taken from the tube-feeding diet, at the beginning and end of an infusion. The volumes were similar in both of the groups and averaged 860 ml on the first day and approximately 1,300 on the second and third days. Significantly greater bacterial contamination was found in the "home-made" tube-feeding diet, particularly with growth of Gram-negative rods. Seven patients (35%) in group 1 and two patients (11.1%) in group 2 developed diarrhoea. This difference is not statistically significant. No correlation was found between hypoalbuminaemia and the development of diarrhoea. It is concluded that powder mixtures and dilution of tube-feeding diets should be avoided on account of the risk of contamination and, similarly, tube-feeding should not be administered for more than 6-8 hours.

Myocardial infarction and cerebral infarction in a Danish suburban community.

A comparison was made of 485 cases of cerebral infarction (CI), registered prospectively in Frederiksberg, Copenhagen, with 495 cases of myocardial infarction (AMI), recorded retrospectively in the same population. The overall annual incidence of AMI was 6.5 per 1,000 population for males, 3.8 for females; the rates for CI were 2.4 and 2.5, respectively. The age-incidence curves, particularly those for AMI, were significantly steeper in the females than in the males. Correspondingly, the male predominance in the AMI-group subsided with age. Age-specific incidence-rates rose exponentially with advancing age; for each sex and diagnosis the relationship can thus be expressed as a simple mathematical formula, which may facilitate comparisons of incidence patterns in different communities. Theories explaining the similarities and differences of the age-incidence curves for AMI and CI are discussed.

Haemodynamic and clinical effects of isosorbide-dinitrate in patients with severe effort angina on beta-blocking treatment.

The effect of isosorbide-dinitrate (ISDN) 20 mg 4 times daily against placebo has been tested in 12 patients with stable effort induced angina pectoris receiving prophylactic treatment with metoprolol. ISDN did not decrease the attack rate or nitroglycerine consumption, nor was exercise tolerance increased after it. Left ventricular function, assessed by radionuclide ventriculography, increased in 6 out of 8 patients (p less than 0.1). It is concluded that ISDN has no place in the treatment of haemodynamically intact patients with severe angina pectoris in spite of beta-blocking treatment, but that it may be of value in the treatment of patients with left ventricular failure, including those whose left ventricular failure has been brought about by beta-blocking treatment necessitated by angina pectoris.