Alkynes reactivity

React at room temperature for up to 3 days (or at 4°C, if the protein is not stable at ambient temperature). The optimal time of reaction is dependent on the protein being coupled and the number of alkyne reactive groups available. An alkynyl-protein added to the nanoparticles at a high molar ratio probably would reach maximal coupling yield in a matter of hours. 

The carbonyl Co2(CO)6 forms stable 7i-complexes of alkynes 0/2 complexes). Four effects on alkyne reactivity are expected from this coordination (i) protection of the triple bond (ii) stabilization of the carbonium ion on the a-carbon (or propargylic cations (iii) syntheses of common and medium-size cycloalkynes and (iv) steric effects. 

Alkynes are somewhat less reactive than alkenes. For example, 1-butene is 20 times more reactive than 1-butyne in 8.24 M112804. " Alkyne reactivity increases with the addition of ERG substituents. Solvent isotope effects are indicative of a ratedetermining protonation. " These reactions are believed to proceed by rate-determining proton transfer to give a vinyl cation. Reactions proceeding through a vinyl cation would not be expected to be stereospecific, since the cation will adopt sp hybridization (see Section 3.4.1). 

A major factor in determining the magnitude of relative rates is the solvent used. Thus, high alkene alkyne reactivity ratios are found in organic solvents of low dielectric constant (acetic acid), but the rates of reaction are comparable when water is the solvent. This is true not only for the hydration but also for bromination. Polar solvents, water in particular, are evidently capable of minimizing the energy difference between the two transition states. Whether this is accomplished by very strong solvation or by some other mechanism is not entirely clear. Addition reactions of alkenes and alkynes with trifluoroacetic acid also take place at comparable rates. ... 

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