Pyrolysis hydrogen bridging

Then, the first limitation of El is related to sample vaporization, usually obtained by heating the sample under vacuum conditions (10 5-10 6Torr) present in the ion source. Unfortunately, for many classes of compounds the intermolecular bonds (usually through hydrogen bridges) are stronger than the intramolecular ones and the result of heating is the pyrolysis of the analyte. The El spectrum so obtained is not that of analyte, but that of its pyrolysis products. As examples of... 

The trienone (74), either by reaction with diazomethane and pyrolysis of the derived pyrazoline or by treatment with dimethylsulphoxonium methylide anion, yielded28 the 1 a,2 -methylene derivative (75). Epoxidation followed by the action of hydrogen chloride gave (77). The methylene bridge was re-formed by the reaction of collidine, the product being (76). Halogenated steroids of use in determining the metabolic fate of 16-chloro-oestrone methyl ethers and of chlormadinone acetate have been synthesized.29... 

Beryllium, aluminium and some transition metals such as thorium differ from the alkali metals in forming volatile borohydrides which constitute the most volatile compounds of these elements. On pyrolysis they decompose giving hydrogen and non-volatile residues. Electron diffraction and infrared studies suggest they possess bridge structures. 

Dehydrogenation of enediones. The adduct (1) of 2,3-dimethoxyquinone and 1,3-dimethoxycyclohexa-l,3-diene is converted into the quinone (2) by enoliza-tion with potassium hydrogen carbonate and oxidation with potassium nitroso-disulfonate. The ethano bridge is lost on pyrolysis at 150° to give the tetramethyl ether of spirochrome-B (3).1... 

The FT-IR spectra for four coals and their vacuum tar are illustrated in Fig 27 For bituminous coals, the two materials are almost identical except for a higher concentration of aliphatic (hydroaromatic) hydrogen (especially methyl) in the tar This extra hydrogen is presumably abstracted from the char to stabilize the free radical sites formed when the bridges were broken Similar arguments were given for pyrolysis of model compounds by Wolfs et al (56) ... 

The bimetallic compound (Pb[CO)9Co3(CCOO)2]) , which is a chain array, results from the bridging carboxylate ligands. One central unit of this material is shown in 16, but without the associated carbonyl groups on the cobalt. Pyrolysis gives a bimetallic product that is a stable heterogeneous catalyst for the hydrogenation of 1,3-butadiene. 

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