Elimination intermolecular

With l,2,2-trifluoro-l,2-dichloroethyl iodide, zinc reacts exothermically, but iodine IS eliminated intermolecularly, the reaction yields 1,2,3,4-tetrachloroper-fluorobutane [72] (equaoon 41)... 

In addition to being additive, intermolecular forces can also be competitive. More specifically, the orientation of the molecules that is optimal to satisfy one type of interaction may not be ideal for another type. The result is a compromise amongst the individual attractive forces to achieve the lowest potential energy state for the crystal. Furthermore, AHm is not the energy required to completely eliminate intermolecular attraction at Tm but the energy required to reduce the attraction to its level in the liquid that level being a function of intermolecular distance. 

Tannin-tannin, tannin-gum, and gum-gum hydrogen bonds. Aqueous tannin extract solutions are not true solutions but, rather, colloidal suspensions in which water access to all parts of the molecules present is very slow. As a consequence, it is difficult to eliminate intermolecular hydrogen bonds by dilution only [42,45]. 

Note the stress on dealing with free (which usually means gaseous) molecules. This eliminates intermolecular forces, and ensures that the enthalpy of atomization depends only on the energies of the bonds in the molecules. Thus, in this Section, we work with gaseous H2O and H2O2 and their thermodynamic properties at 25 °C, even though both substances are liquids at this temperature. 

In the synthesis of molecules without functional groups the application of the usual polar synthetic reactions may be cumbersome, since the final elimination of hetero atoms can be difficult. Two solutions for this problem have been given in the previous sections, namely alkylation with nucleophilic carbanions and alkenylation with ylides. Another direct approach is to combine radical synthons in a non-polar reaction. Carbon radicals are. however, inherently short-lived and tend to undergo complex secondary reactions. Escheirmoser s principle (p. 34f) again provides a way out. If one connects both carbon atoms via a metal atom which (i) forms and stabilizes the carbon radicals and (ii) can be easily eliminated, the intermolecular reaction is made intramolecular, and good yields may be obtained. 

The acylpalladium complex formed from acyl halides undergoes intramolecular alkene insertion. 2,5-Hexadienoyl chloride (894) is converted into phenol in its attempted Rosenmund reduction[759]. The reaction is explained by the oxidative addition, intramolecular alkene insertion to generate 895, and / -elimination. Chloroformate will be a useful compound for the preparation of a, /3-unsaturated esters if its oxidative addition and alkene insertion are possible. An intramolecular version is known, namely homoallylic chloroformates are converted into a-methylene-7-butyrolactones in moderate yields[760]. As another example, the homoallylic chloroformamide 896 is converted into the q-methylene- -butyrolactams 897 and 898[761]. An intermolecular version of alkene insertion into acyl chlorides is known only with bridgehead acid chlorides. Adamantanecarbonyl chloride (899) reacts with acrylonitrile to give the unsaturated ketone 900[762],... 

For elimination of intra- as well as intermolecular energy losses we have synthesized co-polymers - styrene or methylmethacrylate with P-diketones and used them in analysis for the same purpose. In this case the increase of sensitivity of Ln determination as well as selectivity was observed. 

A polyfluorinated P,y-unsaturated ketone is formed m situ from tributylamine and 3,4-bis(tnfluoromethyl)-3-(pentafluoroethyl)-5,5,6,6,6-pentafluoro-2-hex-anone. The enol form of the unsaturated ketone cyclizes via an intermolecular addition-elimination reaction that involves exclusive attack by oxygen rather than by carbon. This reaction demonstrates the hardness of a F-C= site toward... 

The above reaction is a convincing example of an intermolecular hydrogen abstraction leading essentially to the same result as obtained in the pyrolysis of alkyl-substituted thiirane oxides through an intramolecular /(-elimination of hydrogen. 

The Pummerer reaction346 of conformationally rigid 4-aryl-substituted thiane oxides with acetic anhydride was either stereoselective or stereospecific, and the rearrangement is mainly intermolecular, while the rate-determining step appears to be the E2 1,2-elimination of acetic acid from the acetoxysulfonium intermediates formed in the initial acetylation of the sulfoxide. The thermodynamically controlled product is the axial acetoxy isomer, while the kinetically controlled product is the equatorial isomer that is preferentially formed due to the facile access of the acetate to the equatorial position347. The overall mechanism is illustrated in equation 129. 

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