CH2, dimerization

K Me2E14=X Dimer K Me2E14(X)CH2 Dimer K Me2E14=CH2 Dimer... 

Consider, for example, the radical anion from styrene, PhCH=CH2. Dimerization of styrene to a biradical would remove the two terminal carbon atoms from conjugation. The resulting loss in n energy per styrene unit would then be Nt being the corresponding reactivity number, namely... 

Collision-induced dissociation mass spectrum of tire proton-bound dimer of isopropanol [(CH2)2CHOH]2H. The mJz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mJz 103), loss of isopropanol mJz 61) and loss of 42 anui mJz 79). (b) Ion-molecule reactions in an ion trap. In this example the mJz 103 ion was first isolated and then resonantly excited in the trap. Endothennic reaction with water inside the trap produces the proton-bound cluster at mJz 121, while CID produces the fragment with mJz 61. 

Sote 1. In the final stage of the distillation the remaining liquid is subjected to a relatively higli temperature. This causes dimerization of the greater part of the yne-allene RCeC-CH=C=CH2, which is formed as a by product. 

Note 2. During this operation the small amount of CH3C C-CH=C=CH2, present in the crude product, dimerized. 

The two dimers of (CH3)2C=CH2 are formed by the mechanism shown m Figure 6 16 In step 1 protonation of the double bond generates a small amount of tert butyl cation m equilibrium with the alkene The carbocation is an electrophile and attacks a second molecule of 2 methylpropene m step 2 forming a new carbon-carbon bond and generating a carbocation This new carbocation loses a proton m step 3 to form a mixture of 2 4 4 tnmethyl 1 pentene and 2 4 4 tnmethyl 2 pentene... 

Ketenes. Derivatives of the compound ketene, CH2=C=0, are named by substitutive nomenclature. For example, C4Hc,CH=C=0 is butyl ketene. An acyl derivative, such as CH3CH2—CO—CH2CH=C=0, may be named as a polyketone, l-hexene-l,4-dione. Bisketene is used for two to avoid ambiguity with diketene (dimeric ketene). 

Dialkyl and diarylthaHium(III) derivatives are stable, crystalline soHds that melt at 180—300°C. The dimethylthaHium derivatives of CN , CIO, BF, and NO 2 contain linear (CH2)2T1 cations and the free anions (19). In aqueous solutions, they ionize to the (CH2)2T1(H20) ions, except those derivatives containing alkoxide, mercaptide, or amide anions, which yield dimeric stmctures (20,21). 

Thermal stability is enhanced in chelates thus dimethyl-2-methy1pentane-2,4-dio1titanium [23916-35-0] (22) is much more stable than (CH2)3Ti(OCH(CH2)2)2 (68)- The stmcture of the former has been shown by x-ray diffraction to be dimeric and five-coordinate through oxygen bridges. The more highly substituted the six-membered ring, the mote thermally stable the compound. 

Double alkoxides of zirconium with alkah metals of the type MZr2(OR) have been obtained by reaction of alkah metal alkoxides with zirconium alkoxides (220). Although these usually are monomeric derivatives, the reaction between zirconium tetra-/-butoxide [1071 -76-7] and sodium /-butoxide was found (221) to form dimeric NaZr(OC(CH2)2) ]2. 

The diacids are characterized by two carboxyHc acid groups attached to a linear or branched hydrocarbon chain. AUphatic, linear dicarboxyhc acids of the general formula HOOC(CH2) COOH, and branched dicarboxyhc acids are the subject of this article. The more common aUphatic diacids (oxaUc, malonic, succinic, and adipic) as weU as the common unsaturated diacids (maleic acid, fumaric acid), the dimer acids (qv), and the aromatic diacids (phthaUc acids) are not discussed here (see Adipic acid Maleic anhydride, maleic acid, and fumaric acid Malonic acid and derivatives Oxalic acid Phthalic acid and OTHERBENZENE-POLYCARBOXYLIC ACIDS SucciNic ACID AND SUCCINIC ANHYDRIDE). The bihinctionahty of the diacids makes them versatile materials, ideally suited for a variety of condensation polymerization reactions. Several diacids are commercially important chemicals that are produced in multimillion kg quantities and find appHcation in a myriad of uses. 

In view of the facile oxidation of 10.13a-c it is not surprising that some metathetical reactions with metal halides result in redox behaviour. Interestingly, lithium halides disrupt the dimeric structures of 10.13a or 10.13c to give distorted cubes of the type 10.14, in which a molecule of the lithium halide is entrapped by a Ei2[E(N Bu)3] monomer. Similar structures are found for the MeEi, EiN3 and EiOCH=CH2 adducts of 10.13a. In the EiN3 adduct, the terminal... 

Alternatively, thermolysis yields the terminal alkene RCH=CH2. Note that, if propene or higher alkenes are u.sed instead of ethene, then only single insertion into Al-C occurs. This has been commercially exploited in the catalytic dimerization of propene to 2-methylpentene-1, which can then be cracked to isoprene for the production of synthetic rubber (cu-1,4-polyisoprene) ... 

Bis(l-methylimidazol-2-yl)methane and -ketone with the dimer [Rh(CO)2Cl]2 in the presence of sodium tetraphenylborate give the dicarbonyl complexes 68 (X CHj, CO L = CO) where the carbonyl ligands may easily be substituted by the triphenyl phosphine ligands to yield 68 (X = CH, CO L = PPh ) (99JOM(588)69). The bis(l-methylbenzimidazol-2-yl)methane analogs of 68 (X=CH2 L=C0, PPhj) can be prepared similarly. 

For a more complete treatment of the derivations and determination of experimental rate constants (to be discussed briefly below) refer to Ref. 46 for Gramicidin A and Ref. 47 for the malonyl dimer of Gramicidin A. (Malonyl Gramicidin A is formed by deformylation of Gramicidin A and then joining to amino ends together using the malonyl moiety, —CO—CH2—CO—, to form the covalent dimer.)... 

With bulky diphosphines Bu2P(CH2) PBu2 (n = 8-12), similar reactions of the diphosphines with MCl2(PhCN)2 give separable mixtures of monomer, dimer and trimer. With small phosphines (n = 5-7) dimers predominate (Figure 3.48). 

Specific examples where structures have been determined are trans-Pt[Bu2P(CH2) 2PBu2]Cl2 and dimeric [Pd(Bu P(CH2) PBu )Cl2]2 (n = 5, 7, 10). 

Figure 3.47 The dimeric diphosphine-bridged complex [Pd Ph2P(CH2)6PPh2 Cl2]2.

Dimeric complexes like [Cl(NH3)Pt H2N(CH2)4NH2 Pt(NH3)Cl]Cl2 are also being investigated as they bind to DNA in a different way to that involved in cisplatin binding and are active in cisplatin-resistant human tumour cells. They are more potent than cisplatin in lung cancer models in vivo and are likely to go on clinical trials in the near future [204],... 

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