Connection π
The connection π is a Chemical bond which is created between two atoms by covering of orbital of secondary quantum Nombre > 1 (orbital p, D…). Covering is side, i.e. the 2 lobes of the two orbital ones in interaction are parallel, contrary to the case of the connections σ where the lobes of 2 the orbital atomic ones point one towards the other.
The connection π is present in particular in the Alcène S and the Alcyne S.
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Olefinic hydrocarbons: presence of double linkings in a carbonaceous skeleton
- Alkyne compounds: presence of triple connections in a carbonaceous skeleton
The presence of a connection π prevents very free rotation around this connection because it involves a molecular rigidity. It is with this rigidity that the Stéréoisomérie is due some Alcène S or Alcyne S. Moreover the connection π allows the reactions of addition, because it breaks easily, contrary to the connection σ.
Example: the addition of Diiode on the Propyne is done by rupture of the connections π (there remains always the Liaison σ).
A molecule which has several connections π (or a nonflexible connection π and doublets or electronic gaps) shows the characteristic to have several forms mésomères: the electrons are delocalized.
See too
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