Methane radical cation

Figure 6.9. Top to bottom Two possible Jahn-Teller distorted geometries for the methane radical cation and calculated geometry for its energy minimum schematic representation of the SOMO for ethane radical cation SOMOs of three different propane radical cations observed by ESR the SOMO of butane radical cation and SOMOs for two conformers of pentane radical cation.

Varied Methane Cations. The methane molecular ion (methane radical cation, CH4+ ), the parent ion in mass spectrometry, and the methane dication (CH42+) are of great significance and have been studied both experimentally and theoretically.800 802 Recent advanced studies have shown that the methane radical cation, CH4+ has a fivecoordinate planar structure as suggested in early calculations by Olah and Klopman.800... 

The methane radical cation, CH4, is known to Jahn-Teller distort from the symmetric tetrahedral neutral ground state structure to a conformation of C2, symmetry, with two elongated and two shorter CH bonds (1.18 and... 

In the next section we discuss the radical cations generated upon electron transfer from simple -alkanes to holes generated in various matrices upon radiolysis. The ESR spectra observed in these matrices reveal many interesting structural details. We will begin with the special case of the long-elusive methane radical cation, followed by the radical cations of -alkanes and those of branched alkanes. 

Figure 2. Possible Jahn-Teller distorted geometries for methane radical cation.

It is noteworthy, that ab initio calculations even for small molecules give substantially different results depending on the basis set and the method used to take electron correlation into account. These difficulties are illustrated here with the results from three different calculations on two different methane radical cations. At... 

Table 1. Structures and isotropic hyperfine coupling constants (Gauss) of the methane radical cation.

D-lMbeUed Methane Radical Cations CH4, CDH3, CD2H2, CD3W and CD4+... 

Knight et al. observed ESR spectra of a series of selectively deuterated methane radical cations, CH4+, CDH3, CD2H2 , CD3H+ and CD4+, generated and stabilized in a neon matrix at 4 K [53, 54], The observed isotropic /i/coupling constants... 

Table 5.4 Experimental isotropic it/ splittings, aiso (mT) for H and D atoms in D-labelled methane radical cations in neon matrix at 4 K. The table is reproduced from [54] by permission of the American Institute of Physics...

In order to account for the observed fliso values of and D atoms the following rules were proposed for the location (or site) of and D atoms in the radical cation by Knight [54]. (a) Methane radical cation possesses a Civ type geometrical structure with two distinctly different electronic sites, i.e. apical a site and equatorial e site, (b) Site a can accommodate two or D atoms and is coplanar with the carbon p-orbital with an unpaired electron site e can accommodate two atoms and lies in the nodal plane of this same carbon p-orbital, see Fig. 5.13. (c) D atoms... 

The second topic is concerned with Jahn-Teller (J-T) distortion of organic radical cations whose mother molecules have either 7d or Csv structure with a doubly degenerate HOMO. A series of D( H)-labelled methane radical cations (CH4, ... 

Geometry of methane radical cation. (Adapted from reference 301.)... 

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