Interaction donation

Mixtures of HC1 and 2-butyne were reacted in the gas phase in a Pyrex IR cell between 23 and 63°C to yield only (Z)-2-chloro-2-butene.564 The process is suggested to be initiated and the rate determined by surface-assisted proton-alkyne interaction. Donation of the proton occurs from within a multilayer found on the wall, that is, from an HC1 molecule not directly attached to the wall. 

Even in the solid halogens themselves, halophilic secondary interactions (donation from a lone pair of electrons on one X2 molecule to the empty a orbital of another) occur between diatomic molecules in the same layers, giving interatomic distances much shorter within layers than between layers, and a lengthened a bond in the case of I2. This destroys the axial symmetry of the X2 molecule, so that they have nonzero asymmetry parameters (Table 1, Column H) r] = 0.20 for CI2 and for Br2 rj = 0.175 for I2. 

An alternative drivirg force could involve a donor - acceptor interaction. The electron-poor pyridine ring that is coordinated to the copper cation can act as electron acceptor with respect to the aromatic ring of the -amino acid. The fact that donating substituents on the amino acid increase the efficiency... 

The same situation is observed in the series of alkyl-substituted derivatives. Electron-donating alkyl substituents induce an activating effect on the basicity and the nucleophilicity of the nitrogen lone pair that can be counterbalanced by a deactivating and decelerating effect resulting from the steric interaction of ortho substituents. This aspect of the reactivity of thiazole derivatives has been well investigated (198, 215, 446, 452-456) and is discussed in Chapter HI. 

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