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Pham-Cam Nam,a,b
Pascal Gerbauxc,d and Minh Tho Nguyena,*
aDepartment of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001
Leuven, Belgium. E-mail: minh.nguyen@chem.kuleuven.ac.be
bFaculty of Chemical Engineering, University of Danang, Vietnam
cLaboratoire
de Chimie Organique, Université de Mons-Hainaut, Avenue Maistriau 19, B-7000 Mons, Belgium |
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The protonation and methylation of phenylphosphine
(C6H5PH2) and its mono-halogenated derivatives have been studied using ab initio quantum chemical calculations. Density
functional theory (B3LYP) calculations using the 6-311++G(d,p) basis set consistently confirm that protonation of phenylphosphines takes place at the phosphorus atom; the
C4-protonated phenylphosphine lying about 66 kJ mol–1 above the P-protonated isomer. Similarly, methylation of phosphines consistently occurs
at phosphorus. The proton and methyl cation affinities are estimated as follows: PA(phenylphosphine) = 863 ± 10 kJ mol–1 and
MCA(phenylphosphine) = 515 ∓ 12 kJ mol–1. Mono-halogen substitution appears to reduce the proton affinites by up to 20 kJ
mol–1. In this context, following P-protonation of either ameta– or a para-X–C6H4–PH2, an
elimination of the halogen X-atom under collisional activation (CA) conditions is expected to lead to a distonic radical cation, a low-energy isomer being 50 kJ
mol–1 above ionized phenylphosphine. |
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Keywords:
phenylphosphine, halo-phenylphosphines, protonation, proton affinities, methylation, methyl cation affinity, distonic
radical cations, ab initio calculations |
