title: Nucleophilic and electrophilic reactions of polyynes catalyzed by an electric field: toward barcoding of carbon nanotubes like long homogeneous substrates.
abstract: Computational studies at the B3LYP/6-31+G* level were carried out on the addition of pyridine to polyynes (C6-C18) and on the protonation of polyynes by methyl ammonium fluoride under electric fields of 2.5 and 5 MV/cm. The electric field in each case was oriented along the polyyne axis in a direction that enhances the reaction by stabilizing the incipient dipole. It was found that the reaction of pyridine addition is endothermic with a late transition state. The longer the polyynes and the stronger the field, the electric field catalysis was more efficient. Extrapolation of the data to long polyynes shows that at 1000 nm an electric field of 50 000 V/cm will reduce the barrier by 10 kcal/mol. This reduction is equivalent to 7 orders of magnitude in rate enhancement. A similar barrier reduction could be achieved with a 2.5 MV/cm field at a polyyne length of 20 nm. Protonation reactions were found to be much more affected by the electric field. A reduction of the reaction barrier by 10 kcal/mol using a 2.5 MV/cm electric field could be achieved at a polyyne length of 10 nm. Thus the electric field along the long axis of a substrate could induce a gradient of reactivity which could, in principle, enable the barcoding of substrates by using a sequence of reactants having different reactivities.
authors.affiliation: Department of Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel.
authors.forename: Abraham
authors.initials: A
authors.lastname: Yosipof
authors.forename: Harold
authors.initials: H
authors.lastname: Basch
authors.forename: Shmaryahu
authors.initials: S
authors.lastname: Hoz