Infrared active bond hydrocarbons

The Infrared Region 515 12-4 Molecular Vibrations 516 12-5 IR-Active and IR-lnactive Vibrations 518 12-6 Measurement of the IR Spectrum 519 12-7 Infrared Spectroscopy of Hydrocarbons 522 12-8 Characteristic Absorptions of Alcohols and Amines 527 12-9 Characteristic Absorptions of Carbonyl Compounds 528 12-10 Characteristic Absorptions of C—N Bonds 533 12-11 Simplified Summary of IR Stretching Frequencies 535 12-12 Reading and Interpreting IR Spectra (Solved Problems) 537 12-13 Introduction to Mass Spectrometry 541 12-14 Determination of the Molecular Formula by Mass Spectrometry 545... 

One may well wonder why the in-phase cw-CH wag near 690 cm is so much lower in frequency than the in-phase trans-CYi wag near 970 cm" in the infrared spectrum. In Fig. 4.16, the lone CH wag of the C2C=CHC group has a frequency near 825 cm in hydrocarbons. It can be seen that this vibration twists the C C bond. Also in Fig. 4.16 are seen the in-phase and out-of-phase CH wag vibrations in trans- and cis-C—CH==CH—C groups. Only the in-phase wag is infrared active. In the trans isomer this in-phase vibration gives the C=C bond a double twist, and in the cis isomer the... 

Considerable interest in the subject of C-H bond activation at transition-metal centers has developed in the past several years (2), stimulated by the observation that even saturated hydrocarbons can react with little or no activation energy under appropriate conditions. Interestingly, gas phase studies of the reactions of saturated hydrocarbons at transition-metal centers were reported as early as 1973 (3). More recently, ion cyclotron resonance and ion beam experiments have provided many examples of the activation of both C-H and C-C bonds of alkanes by transition-metal ions in the gas phase (4). These gas phase studies have provided a plethora of highly speculative reaction mechanisms. Conventional mechanistic probes, such as isotopic labeling, have served mainly to indicate the complexity of "simple" processes such as the dehydrogenation of alkanes (5). More sophisticated techniques, such as multiphoton infrared laser activation (6) and the determination of kinetic energy release distributions (7), have revealed important features of the potential energy surfaces associated with the reactions of small molecules at transition metal centers. 

Physicochemical properties of L zeolites and of clinoptilolite were studied by adsorption, chromatographic, spectral, and ther-mogravimetric methods. The sodium form of L zeolite is characterized by better adsorption with respect to water and benzene vapor and by higher retention volumes of C C hydrocarbons and CO than potassium and cesium forms. The activation energy of dehydration determined by the thermogravimetric method decreases on going from the sodium to cesium form of L zeolite. When calcium is replaced by potassium ions in clinoptilolite, the latter shows a decreased adsorption with respect to water vapor. The infrared spectra of the L zeolite at different levels of hydration show the existence of several types of water with different bond characters and arrangements in the lattice. 

Ceckiewicz studied the methanol conversion between 25 and 400 C on zeolite H-T (SiOj/AljOj molar ratio of 7.4) with different degrees of decationization and dealumination. By Fourier transform infrared spectroscopy (FT-IR) he found that CH3OH molecules interact principally with the most active 3,600 cm OH groups corresponding to Al-OH bonds. No transformation of methanol occurred at 25 C. The dehydration of methanol to dimethyl ether was the most important reaction between 200 and 300 C. The conversion of methanol to hydrocarbons was evident at temperatures higher than 300 C. The conversion of methanol was less than 100% in all the cases. After... 

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