Vibrational spectra of tetramethoxymethane (TMM), tetraethoxymethane (TEM), tetramethoxysilane (TMS) and tetraethoxysilane (TES) have been recorded and assigned. DTA curves and temperature vs. time curves have been recorded in the region −150 to + 30°. No transition points have been observed, melting ranges are −1 to +2 (TMM); −16 to −12 (TEM); +10 to +16 (TMS) and −71 to −68° (TES).
The liquid state of tetramethoxymethane (TMM) contains two rotamers; the skeleton C(OC)4 may have S4 or D2d symmetry. The S4 form is about 1 kcal/mole more stable than the D2d form of TMM in the liquid. Solid TMM consists probably of the D2d configuration only.
There is no distinction between either configuration in tetramethoxysilane (TMS) as the rotation of methoxy groups around their SiO axes is apparently free for practical purposes.
The methyl group of an ethoxy group in X(OC2H5)4 may occupy a gauche or a trans position relative to its XO bond. Rotational isomerism of this kind is probably present in tetraethoxymethane (TEM).
Rotational isomerism is probably absent in tetraethoxysilane (TES).
The vibrational spectra (Raman and infrared) of tetrakis(methylthio)methane, tetrakis(ethylthio)methane, tetrakis(methylthio)silane, tetrakis(methy1thio)germane and tetrakis(methy1thio)stannane have been recorded and analyzed with an assignment of the frequencies observed. The vibrational spectrum of tetrakis-(isopropy1thio)methane has been obtained also.The liquid states of tetrakis(methy1thio)methane (TMC), -silane (TMSi) and -germane (TMGe) contain probably two rotamers; liquid and solid tetrakis-(methy1thio)stannane (TMSn) contain probably one configuration in which internal rotation is nearly free.Solid TMC shows a remarkable behaviour concerning the rotamers: modification 1, which is stable at temperatures below 23", contains only the D,, configuration; modification 2, stable between 23" and 46", contains only the Sq configuration and modification 3, stable between 46" and the melting point, consists of a mixture of both configurations.Rotamers present in solid and liquid tetrakis(ethy1thio)methane (TEC) are at least partly different. Raman spectra of solid TEC at temperatures above and below the transition point at -94" are identical within errors of measurement.Solid TMSi and TMGe consist in all probability of one of the rotamers present in the liquid.
Trimethylsulfonium bromide (CH3)3SBr has been prepared; melting range 183‐186°C. Infrared absorption and Raman spectra have been recorded and assigned.
The redundancy relations among thc bending coordinates around a central atom have been derived to second order approximation by means of spherical trigonometry. The formalism derived here is not always applicable. A numerical result is more easily obtained by means of the formalism given here than in the generally applicable methods proposed by Crawfordl and Cihla and Pliva z.
IntroductionIn solving the normal coordinate problem of the vibrational motions in a molecule one tries to connect the vibrational potential energy function V, with the vibrational parameters 1. V, may be developed quite generally as a power series of the internal displacement coordinates Si 3 * 4 :
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