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Evidence of Sn adatoms quantum tunneling at the alpha-Sn/Si(111) surface

Fabio Ronci1, Stefano Colonna, Antonio Cricenti

  • 1ISM CNR, Via del Fosso del Cavaliere 100, I-00133 Roma, Italy. ronci@ism.cnr.it

Physical Review Letters
|November 13, 2007
PubMed

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SN2 Reaction: Transition State

An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
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Electrophilic Addition to Alkynes: Halogenation

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Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
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