Cyclopentadienyl cation, molecular

In the case of the cyclopentadienyl cation, there are only two electrons in the e" tt molecular orbitals that are degenerate in Dji, symmetry. The MO heatments... 

N t/ l Five cyclopentadienyl molecular orbitals 4f Cyclopentadienyl cation (four 77 electrons) 4f Cyclopentadienyl radical (five 77 electrons) -H- Cyclopentadienyl anion (six 7r electrons)... 

Molecular mechanics and ab initio calculations on the cyclopentadienyl cation have been carried out an allylic stmcture is favoured. Calculations referring to the initiation of polymerization of 1,1-disubstituted cyclopropanes by cations (also neutrals and anions) are reported. Rate constants for the solvolyses of (69) show reasonable Yukawa-Tsuno correlations, interpreted in terms of the less reactive substituents... 

A molecule with An n electrons in the ring, with the molecular orbitals made up from An p orbitals, does not show this extra stabilisation. Molecules in this class that have been made include cyclobutadiene 1.13 (n = 1), the cyclopentadienyl cation 1.14, cyclooctatetraene 1.15 andpentalene 1.16 (n 2), [12]annulene 1.17 (n = 3) and [16]annulene 1.18 (n A). 

The distribution of electrons in the tt molecular orbitals of (a) benzene, (b) the cyclopentadienyl anion, (c) the cyclopentadienyl cation, and (d) cyclobutadiene. The reiative energies of the tt molecular orbitals in a cyclic compound correspond to the relative levels of the vertices. Molecular orbitals below the midpoint of the cyclic structure are bonding, those above the midpoint are antibonding, and those at the midpoint are nonbonding. 

The distribution of electrons in the rr molecular orbitals of (a) benzene, (b) the cyclopentadienyl anion, (c) the cyclopentadienyl cation, and (d) cyclobutadiene. 

The mass spectra of phenols usually show strong molecular ion peaks. In fact, the molecular ion at miz = 94 is the base peak in the El-MS of phenol (Fig. 4.34). Favored modes of fragmentation involve loss of a hydrogen atom to create an M - 1 peak (a small peak at mIz = 93), loss of carbon monoxide (CO) to produce a peak at M -28 (m/z = 66), and loss of a formyl radical (HCO-) to give a peak at M - 29. In the case of phenol itself, this creates the aromatic cyclopentadienyl cation at m/z = 65. In some cases, the loss of 29 mass units may be sequential initial loss of carbon monoxide followed by loss of a hydrogen atom. The mass spectrum of ortho-cresol (2-methylphenol) exhibits a much larger peak at M - 1 (Fig. 4.35) than does unsubstituted phenol. Note also the peaks at miz = 80 and m/z = 79 in the o-cresol spectrum from loss of CO and formyl radical, respectively. 

At present, the difficulties described in 7-9 can be solved. The use of MAO can be avoided by the use of non-MAO catalysts such as cationic Group 4 metallocenes or neutral Group 3 metallocenes. It has been found that the molecular weight of the resulting polymer can be increased by introducing substituents at the 2,5-position in the cyclopentadienyl group of the... 

FIGURE 16. Molecular fractions of polymeric lithium cyclopentadienyl derivatives in the solid-state. The cations of the lithocene anions 47 and 48 (Ph4P+ and [(12-crown-4)2Li], respectively) have been omitted for clarity. With 55 the cation is [(THF)4Li]+. AU three are solvent-separated ion pairs. 

FIGURE 70. Molecular geometry of the MeMg(14-N-4) cation and the cyclopentadienyl anion 148a... 

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