The Raman and infrared spectra of CF4 have been recorded in its liquid and two crystalline phases. In the liquid, rotational wings along side some of the fundamentals and the appearance of some forbidden infrared bands reveal the high degree of molecular disorder characteristic of this phase. Very little change occurs in the spectra at the liquid–solid transition; the spectra of Phase I thus appear to be those of a plastic crystal. Marked changes are observed upon cooling to Phase II. The splitting of the fundamentals in the Phase II spectra of CF4 is best interpreted in terms of a S4 tetragonal structure, with the molecules lying on sites of S4 symmetry.
'I'riacyloxyboranes ((RC0z)aB) are obtained in good yields by the action of organic acids on boron sulfide or on o-thioboric acid esters.\Ye have reported previously that functional groups bearing labile hydrogens, such as alcol~ols (I), mercaptans (2), and anlines (3), react with boron sulfide to form B-0, B-S, and B-N bonds, respectively. Besides this sensitivity towards protons, boron sulfide can also react with aldehydic or lretonic carbonyls a t rooin temperature to give the corresponding thioaldehydes or thiolretones. Under more energetic conditions deoxygellation has been noted with esters (4). With o-thioboric acid esters, carbonyls are readily transformed into their corresponding thioacetals a t rooin tenlperature (5). A study has been undertaken to determine the reactivity of the acid function towards boron sulfide and o-thioboric acid esters, the carbonyl group or the hydroxyl group or both being able a priori to react accordiilg to the pattern outlined above.We have found that both aliphatic and aromatic organic acids react smoothly with boron sulfide to give the corresponding triacyloxyboranes (eq. [I]).'The triacyloxyborane is also obtained if an o-thioboric acid ester is used instead of boron sulfide (eq. [ 2 ] ) . \Ale have noted that the carbonyl group is not affected by the o-thioboric acid ester.The mechanism of this reaction should call for the formation of a coinplex bet~veen the electron-poor boron atom and the acidic group, these groups being good acceptors and good donors, respectively. The forination of this complex should be facilitated by the assistailce of hydrogen bonding between neighboring sulfur and hydrogen atoms. By subsequent electron shift, the rupture of the B-S bond and the forination of the 13-0 bond would follolv ( eq. [3]).-.
The Raman and infrared spectra of liquid and crystalline SiF, have been recorded. The assignment of some of the Raman bands of the crystal to longitudinal modes has been confirmed by the infrared reflection spectrum. These indicate that the crystal structure is not centrosymmetric. In other respects the spectra are also more complicated than is expected on the basis of the previously reported Td3 structure. Possible explanations are discussed.On a enregistre les spectres Raman et infrarouges de SiF4 dans ses Ctats condenses. Certaines bandes Raman du cristal, attribuCes a des modes longitudinaux de par le spectre de reflexion infrarouge, indiquent que la structure du cristal n'est pas centrosymetrique. Les spectres sont par ailleurs plus compliquCs que ceux predits d'apres la structure cristalline Td3 proposCe antkrieurement. On apporte quelques explications a ces anomalies.
The overwhelming number of electrocardiograms (ECGs) now recorded routinely has prompted the development of computer analysis which in turn has benefited electrocardiography with important technological advances. All automated ECG analysis systems adopt a similar approach: a measurement program and a program that interprets the clinical significance of these measurements along with a rhythm analysis algorithm. Measurement, selection and classification of parameters vary according to the program used. Data compression is applied to the signal to reduce processing time and allow long-term storage. Diagnostic accuracy, however, is not greatly improved over that of experienced cardiologists. Programs studied using a validated data bank provided by an international group of cardiologists show a variability not only in parameter measurement but also in diagnostic statement and in the way in which such statements are expressed. Recommendations for measurement standards have been made to fulfil the need for exchange of diagnostic criteria. No recommendations concerning the selection of parameters have been proposed, and so new parameters or combinations of parameters can be introduced with the ultimate aim of increased diagnostic performance.
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