Alkyl fragments

This catalytic reaction has been named alkane a-bond metathesis since alkyl fragments of alkane mixtures are exchanged. For example, propane is... 

G and H. This suggests that the isomerization of the surface alkyl fragments inter-converting D, E, and F, is slow with respect to the second carbon-hydrogen bond activation step and subsequent carbon-carbon bond cleavage. 

Method G is used to introduce the alkyl fragment when less reactive alkenes are employed or for cases where functionality within the dienophilic alkene undergoes reaction with the Grignard reagent. Following this procedure, a lithium anion is first added to the aldehyde 5 at 78 °C.27 After consumption of the aldehyde has been determined by TLC, the dienophile is added and magnesium bromide is introduced. The cycloaddition occurs as the reaction warms to room temperature. In the case of... 

The field of alkyl and aryl Co complexes in low formal oxidation states has been extensively studied, and is frequently associated with cluster chemistry.92 Alkyl and aryl ligands, with or without additional functionality, are often co-ligands with tt acceptors such as carbonyls and/or phosphines, e.g., (MeOCOCH2)Co(CO)3(PPh3).93 A simple example of a cluster is (RC)Co3(CO)9, where the triangular Co(CO)3 3 moiety is capped by the 73-alkyl fragment, which occupies the apex of a distorted Co3C tetrahedron. 

However, if protons at the a-carbon atom of the O-alkyl fragment are absent, another process can occur resulting in elimination of olefin and generation of the respective aci-nitro compound (Eq.2). In particular, this anomalous decomposition was found by Nenitzescu and Isacescu (234) for nitronate 74a (Eq. 3). 

APCI and ESI-FIA-MS-MS examinations in the positive and negative mode were performed. The product ions of the [M + NH4]+ parent ion m/z 394 from the feed extract allowed an unequivocal identification of the homologue as ion of the AE molecule with the formula Ci3H27—O—(CH2—CH2—0)4—H. The product ions m/z 45, 89, 133 and 177, known as ethoxylate fragments of the PEG chain, and the alkyl fragments m/z 57, 71, 85, 99,113 and 127 were also characteristic [7] for this AE type, which is presented with its fragmentation scheme in Fig. 2.9.4 [22],... 

Triton X-200 is known to be hardly biologically degradable. To confirm this behaviour, the compound characterised as NPE0-CH2-S03 containing two EO units in the ethoxy chain (NP(E0)2-S03) was submitted to a LC separation. RT comparison in APCI-LC-MS(+/-) experiments and APCI-FIA-MS-MS in the product ion mode were examined (Fig. 2.11.20(a)) in positive and negative modes [15]. In the positive CID spectrum of NP(E0)2-S03, the parent ion 420 disappeared and the product ion m/z 291 (cf. inset in Fig. 2.11.20(a)) known as the characteristic NPEO product ion was observed as base peak [22]. Application of CID furthermore led to alkyl fragments (m/z 57, 71, and 113) and ions at m/z 165 and 121 resulting from the abstraction of the alkyl chain of ion 291 or from the abstraction of the alkyl chain and one... 

Alkyl fragments result from rupture of the aromatic ring. (3-scission of phenyl radical will yield n-C4H3 and acetylene ... 

Radical chemistry has seen tremendous progress in the past two decades and can now be considered as an eminent sub discipline in synthetic organic chemistry [1-6]. Diastereoselective radical chemistry is well established and many examples of enantioselective radical reactions have appeared in the recent literature. For reviews on diastereoselective radical chemistry see [7-11] for reviews on enantioselective radical chemistry see [12-16] and for reviews on conjugate additions, see [17,18]. This review will detail different ways to introduce asymmetry during a radical reaction. These transformations can be broadly classified into atom transfer reactions, reductive alkylations, fragmentations, addition and trapping experiments, and electron transfer reactions. 

The results of path B and its alkyl fragment are shown next in Scheme 18.2. This essentially amounts to loss of CO, with the radical fragments staying close enough to each other in the cage to allow facile recombination. The resultant product, after hydrolysis, gives the p-hydroxycthoxy benzoic acid reported [21],... 

If the side chain is in an iso form, a more complex aromatic olefin forms. Isopropyl benzene leads to a methyl styrene and styrene [70], The long-chain alkylate aromatics decay to styrene, phenyl, benzyl, benzene, and alkyl fragments. The oxidation processes of the xylenes follow somewhat similar mechanisms [71, 72],... 

Upon extrapolation to larger ketones one can expect to observe larger acylium and alkyl fragments. The occurrence of series of homologous ions is a feature that can be very helpful to deduce structural information from mass spectra. Ions such as the acylium ion series and the carbenium ion series are also known as characteristic ions. Learning the nominal masses of the first members of each series by heart is useful (Tables 6.2 and 6.3). 

Consequently, this reaction could be identified with a process where an alkyl fragment is transferred from one alkane molecule to another. The methyl group is the smallest alkyl fragment and the easiest to be transferred. However, crossmetathesis shows that ethyl and propyl groups can also be transferred. Indeed, heavier homolog alkanes can result from successive reactions or from heavier alkyl group transfer. Consequently, because of the successive reactions, the real product distribution corresponds to the following equation ... 

H MAS NMR clearly shows five signals at 0.8, 1.9, 4.4, 10.1 and 12.1 ppm. The signals at 0.8, 1.9 and 4.4 are assigned to alkyl fragments bonded to silicon atoms, residual silanol groups on the silica surface and to silicon hydride species, respectively. The two downfield signals at 10.1 and 12.1 ppm are an indication of the presence of two types of zirconium hydride surface species [111]. DQ rotor-synchronized 2D H MAS NMR was used to discriminate these zirconium hydride... 

In order to process the emended data in as unprejudiced a manner as possible, we adopted as our fundamental variable for correlating structure with affinity the intramolecular distance of an alkyl fragment of a bound ligand from its ammonium ion. The rationale for this approach is that the binding site for the... 

C—O bond cleavage with the charge remaining on the alkyl fragment. 

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