Search results
Results From The WOW.Com Content Network
Since thermal electrocyclic reactions occur in the HOMO, it is first necessary to draw the appropriate molecular orbitals. Next, the new carbon-carbon bond is formed by taking two of the p-orbitals and rotating them 90 degrees (see diagram). Since the new bond requires constructive overlap, the orbitals must be rotated in a certain way.
The p z orbital is the same as the p 0 orbital, but the p x and p y are formed by taking linear combinations of the p +1 and p −1 orbitals (which is why they are listed under the m = ±1 label). Also, the p +1 and p −1 are not the same shape as the p 0 , since they are pure spherical harmonics .
In the usual analysis, the p-orbitals of the metal are used for σ bonding (and have the wrong symmetry to overlap with the ligand p or π or π * orbitals anyway), so the π interactions take place with the appropriate metal d-orbitals, i.e. d xy, d xz and d yz. These are the orbitals that are non-bonding when only σ bonding takes place.
The other two p-orbitals, p y and p x, can overlap side-on. The resulting bonding orbital has its electron density in the shape of two lobes above and below the plane of the molecule. The orbital is not symmetric around the molecular axis and is therefore a pi orbital. The antibonding pi orbital (also asymmetrical) has four lobes pointing away ...
When comparing localized molecular orbitals derived from the same atomic orbitals, these classes generally follow the order σ < π < n < p (n*) < π* < σ* when ranked by increasing energy. [ 20 ] The localized molecular orbitals that organic chemists often depict can be thought of as qualitative renderings of orbitals generated by the ...
The p orbital can hold a maximum of six electrons, hence there are six columns in the p-block. Elements in column 13, the first column of the p-block, have one p-orbital electron. Elements in column 14, the second column of the p-block, have two p-orbital electrons. The trend continues this way until column 18, which has six p-orbital electrons.
For the hydrogen fluoride molecule, for example, two F lone pairs are essentially unhybridized p orbitals of π symmetry, while the other is an sp x hydrid orbital of σ symmetry. An analogous consideration applies to water (one O lone pair is in a pure p orbital, another is in an sp x hybrid orbital).
To summarize, we are assuming that: (1) the energy of an electron in an isolated C(2p z) orbital is =; (2) the energy of interaction between C(2p z) orbitals on adjacent carbons i and j (i.e., i and j are connected by a σ-bond) is =; (3) orbitals on carbons not joined in this way are assumed not to interact, so = for nonadjacent i and j; and ...