Conformation effect on reactivity

Conformational effects, on reactivity of cycloamyloses, 23 242, 245-249 Constant Ci, values for, 33 273, 274 Contact catalysis, mechanism of, 2 251 Contact catalysts, surface area measurements for studying, 1 65... 

Counterion effects similar to those in ionic chain copolymerizations of alkenes (Secs. 6-4a-2, 6-4b-2) are present. Thus, copolymerizations of cyclopentene and norbomene with rhenium- and ruthenium-based initiators yield copolymers very rich in norbomene, while a more reactive (less discriminating) tungsten-based initiator yields a copolymer with comparable amounts of the two comonomers [Ivin, 1987]. Monomer reactivity ratios are also sensitive to solvent and temperature. Polymer conformational effects on reactivity have been observed in NCA copolymerizations where the particular polymer chain conformation, which is usually solvent-dependent, results in different interactions with each monomer [Imanishi, 1984]. 

Conformational effects on reactivity can be considered under the heading of steric effects,11 though in these cases we are considering not the effect of a group X and that of another group X upon reactivity at a site Y but the effect of the conformation of the molecule. Many reactions fail entirely unless the molecules are able to assume the proper conformation. An example is the rearrangement of N-benzoylnorephedrine. The two dia-... 

If two different three-dimensional arrangements of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are conformations otherwise, they are configurations. Configurations represent isomers that can be separated however, conformers cannot be separated. Conformational effects on reactivity may be considered under the steric effects. 

Many of the conformational effects on reactivity can be described and analyzed in terms of the difference between van der Waals interactions in the ground state and the transition state. Some cyclic molecules contain another type of strain, known as angle strain, resulting from distortion of bond angles from optimal values. We would now like to consider how such distortions might effect reactivity. 

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