Reinhard Mecke

Konformative beweglichkeit flexibler ringsysteme. Untersuchungen mit hilfe der protonenresonanz-spektroskopie—VI. Mitteilung: Eine erweiterung und verfeinerung des verfahrens zur bestimmung der aktivierungsenergie

Abstract The methods to evaluate the lifetime of conformative molecular states by measurementsof the temperature dependence of proton resonance, have been refined and extended. For this purpose, the apparent line width is divided into two components, the temperature dependence of each being studied. It is shown, that also that part of the total line width which is not influenced by the exchange, the “Eigenbreite”, depends on temperature. The temperature dependence of the “Eigenbreite” has to be considered when using the various methods for the determination of τ, especially when the “Eigenbreite” is relatively large compared to the chemical shift. The efficiency of the method is demonstrated for some examples, i.e. ring compounds, for which the proton resonance signals of two pairs of geminal ligands, on different places in the ring system, can be analysed separately.

Spektroskopische untersuchungen an organischen ionen—III: Das infrarot-spektrum und die struktur des thiohamstoff-kations (thiouromum-ions), des s-methyIthiouromum-ions, des thioacetamid-kations und des thioacetamid-kupfer(I)chlorid-komplexes

Abstract The cations, which are present in the salts of thiourea and thiouacetamide, respestively, with strong acids are sulphonium ions formed by addition of the proton to the sulphur atom. The normal vibrations of these ions as well as those of their free “bases” are assigned. The spectral changes on salt formation are chiefly due to changes in π-electronic structure.

Frequenzen und normalkoordinaten der nicht-ebenen normal-schwingungen von symmetrischen ortho-, meta-, 1:3:5-und hexasubstituierten benzolderivaten

Abstract Using the model described by Whiffen [1] the frequencies of the out-of-plane normal vibrations and the normal co-ordinates of symmetrically substituted benzene derivatives including the ortho-, meta- , 1:3:5- and hexa-forms have been calculated. The calculated frequencies are compared with the frequencies observed in the Raman and infra-red spectra, and an assignment is given.

Spektroskopische Untersuchungen an organischen Ionen—V Die Struktur der Salze des Acetamids

Abstract The vibrational frequency assignment is given for acetamide in the gas phase, in solution and in the two known crystal modifications. From a study of two metal complexes of the neutral acetamide it is evident that the acetamide molecule is attached to the metal by the oxygen atom. The structure of the acetamide cation formed by addition of a proton to acetamide is shown to be an oxonium type ion Download : Download full-size image The frequency assignments of this cation as well as the acetamide anion formed by removal of a proton are also given. The structures of the heavy metal salts of acetamide, which are supposed to be “inner complexes” are discussed.

IR-spektroskopische Untersuchungen über die Rotationsisomerie bei 2-substituierten Äthanolen

ZusammenfassungBei den 2-substituierten Äthanolen der allgemeinen Form X-CH2-CH2-OH konnten von den fünf zu erwartenden Rotationsisomeren IR-spektroskopisch nur zwei, die all-trans-Form und die geschlossene gauche-Form nachgewiesen werden. Sofern man im gasförmigen oder flüssigen Aggregatzustand bzw. in Lösung untersucht, stehen beide Konfigurationen miteinander im thermodynamischen Gleichgewicht. Als Schlüsselbanden zur Unterscheidung der beiden Rotationsisomeren sind die zwei Teilbanden der OH-Valenzschwingung (νOH trans und νOH gauche) herangezogen worden. Das Verhältnis ihrer relativen Intensitäten erlaubt qualitative Rückschlüsse auf die Stabilität der beiden Gleichgewichtspartner und auf die Lage des Gleichgewichts selbst.

Spektroskopische Untersuchungen an organischen Ionen-I: Das Schwingungsspektrum des Acetamidinium- und des N-d4-Acetamidinium—Ions

Abstract The infra-red spectra of the acetamidinium ion [H 3 C−C(NH 2 ) 2 ] + both in the chloride and in salts with complex anions of type MeCl 6 − as well as the spectrum of the deuterated ion [H 3 C−C(ND 2 ) 2 ] + are assigned in terms of normal vibrations assuming a C 2 v -model. The interpretation of the spectra proves the structure assumed. Comparing the spectrum of the acetamidinium ion with those of its deuterated analogue and of isoelectronic ions leads to the conclusion that the assignment proposed by Davies and Parsons [3] is to be improved. The advantage of using complex salts in i.r.-spectroscopic studies of organic cations [4] is emphasized.

Spektroskopische Untersuchungen an organischen Ionen—II: Das Infrarot-Spektrum des Guanidinium-Ions in verschiedenen Salzen

Abstract The vibration frequencies of the guanidinium ion in a series of salts has been measured. Differences in the spectra are attributed to hydrogen bonding to the anions of different strengths.

Kraftkonstantenberechnung an molekülen der symmetriegruppe D3h

Abstract From the vibration frequencies of the molecules BF3, BCl3, BBr3, BJ3, BO33−, CO32−, NO3− und C(NH2)3+ the force constants of a valence force field are calculated using an electronic analog computer. The solutions are presented graphically. If available the frequencies of isotopic molecules are used to find a unique solution, but in the case of BBr3 and BJ3 the isotope effect is too small to be of any practical value, whereas for BF3 and BCl3, it is just sufficient to set rather broad limits for the true potential function of the molecules.

Kraftkonstantenberechnung an einigen ebenen Molekülen vom Typ XZY2

Abstract The calculation of force constants of a valence force field including interactions from molecular vibration frequencies is a problem which in general has no unique solution. Therefore a number of different potential functions, all of which are in agreement with the observed molecular frequencies, are calculated for some planar molecules of the type XZY 2 under different assumptions, and the resulting sets of force constants are compared and discussed, in order to find solutions which probably are close to the true nature of the molecules. The following molecules are treated: CO(CH 3 ) 2 ; CO(NH 2 ) 2 ; CH 3 CO 2 − ; CH 3 C + (NH 2 ) 2 ; OHC + (NH 2 ) 2 ; COF 2 COCl 2 and COBr 2 .

Absorptionsintensitäten der CH- und CD-Valenzschwingungen deuterierter Benzol-Isotope

Abstract The absorption intensities of the CH- and CD-stretching vibrations of the deuterated benzene isotopes C 6 H 6 , C 6 H 5 D, p -C 6 H 4 D 2 , symC 6 H 3 D 3 , and C 6 D 6 have been measured in CCl 4 solution. Independent of the molecular symmetry and the actual form of the normal vibrations each CH(CD) oscillator gives a constant contribution of 0,099 cm 3 /mol to the integrated intensity in the region of the CH- or CD-stretching vibrations respectively. This is a special case of the “Isotope Intensity Sum Rule”. 1. 1. Die Frequenzen der CH- bzw. CD-Valenzschwingungen der gemessenen Benzol-Isotope fallen auf einen engen Bereich zusammen. Die durch Kopplung bewirkte Frequenzaufspaltung betragt maximal 2% des Absolutwerts. 2. 2. Die Absorptionsschwerpunkte fallen fur alle Isotope zusammen. Das Frequenzverhaltnis ν CH /ν CD ist um nur 2% kleiner, als man fur vollig ungekoppelte Oszillatoren erwartet. 3. 3. Die einzelnen Bindungen geben unabhangige Beitrage zur gesamten integralen Intensitat in ihrem Frequenzbereich. 4. 4. Zur Bestimmung der integralen Intensitat mussen samtliche Banden in dem Frequenzbereich erfasst werden, auch wenn ihre Zahl die Zahl der IR-aktiven Schwingungen ubersteigt. Diese Resultate werden in folgenden Untersuchungen benutzt werden, um den Einfluss von Substituenten auf die einzelnen CH-Bindungen in Benzolderivaten durch Intensitatsmessungen zu erfassen [9]. Wahrend die Bindungsintensitaten bei unsubstituiertem Benzol in allen Bindungen gleich sind, werden sie bei den Derivaten in unterschiedlichem Mas mit der Stellung zum Substituenten variieren.