Allyl cation electronic configuration

It was suggestedthat bicyclobutane formation from conjugated dienes occurs in a concerted fashion from vibrationally relaxed singlet having an allyl anion-methyl cation electronic configuration. 

Electronic Configurations of the Allyl Radical, Cation, and Anion 681... 

The electronic configuration of the allyl cation (Figure 15-12) differs from that of the allyl radical it lacks the unpaired electron in tt2, which has half of its electron density on Cl and half on C3. In effect, we have removed half an electron from each of Cl and C3, while C2 remains unchanged. This MO picture is consistent with the resonance picture showing the positive charge shared by Cl and C3. 

Q Show how to construct the molecular orbitals of ethylene, butadiene, and the allylic Problems 15-35 and 36 system. Show the electronic configurations of ethylene, butadiene, and the allyl cation, radical, and anion. 

Fig. 7a and b. Interconversion of cyclopropyl and allyl cation (1), radical (2), and anion (3) correlation diagrams for electron configurations and states a) conro-tatorymotion b) disrotatory motion... 

There is a third kind of orbital called a non-bonding orbital. Electrons in these orbitals neither strengthen nor weaken the bonding between atoms. The 7r-electron configurations for the ground states, and first excited states of the allyl cation, free radical, and anion are ... 

Manganese group olefin compounds have electronic configuration (Table 6.14). Cationic complexes such as [Mn(CO)5 (olefin)] are not formed from the unstable Mn(CO)g but from the chlorocarbonyl compound Mn(CO)5Cl and olefin in the presence of AICI3, or by protonation reaction of <7-allyl compounds ... 

The ground-state tt-electron configuration of the allyl system is built up by putting electrons in pairs into the MOs, starting with those of lowest energy. Thus far, we have been describing our system as the allyl radical. However, since we have as yet made no use of the number of tt electrons in the system, our results so far apply equally well for the allyl cation, radical, or anion. 

Stereochemistry A Pd(0) complex displaces allylic leaving groups (with inversion of configuration) to generate cationic Tr-allyl palladium species A. This complex is electronically deficient and undergoes attack of a suitable soft nucleophile (with inversion) to give a product with overall retention (Scheme 5.8). 

Figure 29.7. Allyl system. Configuration of tt electrons in cation, free radical, and anion.

A series of 7r-allyl-Fe(CO)3 cationic complexes has been obtained by treatment of diene-Fe(CO)3 complexes with strong acids such as HBF4 or HCIO4 50). These complexes are unusual in that the Fe atom is two electrons short of having the next inert gas configuration. Thus reaction of butadiene-Fe(CO)3 with HBF4 produces anft-l-methyl-w-allyliron tricarbonyl fluoroborate (XCI) while protonation of ra tt-l,3-pentadiene-... 

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