Acetylene deprotonation energy

The calculated deprotonation energies of ethane, ethylene and acetylene by SCF Hartree-Fock (FIF) and MP2 methods follow the expected order 456, 455 (basis... 

Regarding the first problem, the most elemental treatment consists of focusing on a few points on the gas-phase potential energy hypersurface, namely, the reactants, transition state structures and products. As an example, we will mention the work [35,36] that was done on the Meyer-Schuster reaction, an acid catalyzed rearrangement of a-acetylenic secondary and tertiary alcohols to a.p-unsaturatcd carbonyl compounds, in which the solvent plays an active role. This reaction comprises four steps. In the first, a rapid protonation takes place at the hydroxyl group. The second, which is the rate limiting step, is an apparent 1, 3-shift of the protonated hydroxyl group from carbon Ci to carbon C3. The third step is presumably a rapid allenol deprotonation, followed by a keto-enol equilibrium that leads to the final product. 

Houk, Schleyer, and co-workers studied the nucleophilic additions of lithium hydride and methyllithium to acetylene and ethylene, respectively [135, 136]. The best estimate of the activation energy from Schleyer s study is 3 kcal/mol for the reaction of acetylene with lithium hydride. There is a negligible difference in the calculated activation energies of the acetylene-LiH and ethylene-LiH reactions, although acetylene appears to form a weaker n-complex with LiH than ethylene does. The competitive deprotonation processes were also considered by these and other workers [137]. 

Despite their high dissociation energy of 133 kcal/mol, sp C—H bonds are prone to C—H bond activation. Indeed, the simplest alkyne, acetylene, has a rather small pR, value of25—26, which makes it a weak acid in organ-ometaUic chemistry, and can be deprotonated by a strong base such as a nitrogen- or carbon-based anion. Therefore, the reaction between a metal alkyl complex and a primary alkyne is usually thermodynamically favorable and resembles a classical acid—base metathesis reaction. 

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