Methyl anion, bonds

Draw Lewis structures for methyl anion, ammonia and hydronium cation. How many electrons are left over in each after all bonds have been made Display and compare electron density surfaces for methyl anion, ammonia and hydronium cation. Which is the smallest molecule Which is the largest Rationalize your observation. (Hint Compare the number of electrons in each molecule, and the nuclear charge on the central atom in each molecule.)... 

It is reasonable to relate the values of k+fk at least qualitatively to the extents of bond making and breaking in the transition state. Bond making is all important in hydrolyses of carboxylic anhydrides, diaryl carbonates and methyl arenesulfonates. Bond breaking will be important in hydrolyses of alkyl halides and sulfonates, except for methyl derivatives, and especially so in water which can effectively solvate the leaving anion. 

Insertion and migration refer to the process in which an unsaturated molecule inserts to a metal-anion bond. The two ways of describing this elementary step have been depicted in Figure 2.2 and 2.3 In the platinum complex shown an acetyl fragment is formed from a co-ordinated CO and a methyl group, both attached to platinum. Clearly, the two reacting groups should occupy positions cis to one another, otherwise the reaction cannot occur [1]. 

A very useful thermodynamic cycle links three important physical properties homolytic bond dissociation energies (BDE), electron affinities (EA), and acidities. It has been used in the gas phase and solution to determine, sometimes with high accuracy, carbon acidities (Scheme 3.6). " For example, the BDE of methane has been established as 104.9 0.1 kcahmol " " and the EA of the methyl radical, 1.8 0.7 kcal/mol, has been determined with high accuracy by photoelectron spectroscopy (PES) on the methyl anion (i.e., electron binding energy measurements). Of course, the ionization potential of the hydrogen atom is well established, 313.6 kcal/ mol, and as a result, a gas-phase acidity (A//acid) of 416.7 0.7 kcal/mol has been... 

Methane, with its relatively nonpolar bonds, is inert to almost all reagents that could remove hydrogen as H or H e except under anything but extreme conditions. As would be expected, methyl cations CH3 and methyl anions CH3 e are very difficult to generate and are extremely reactive. For this reason, the following reactions are not observed ... 

Three reactive species, a methyl anion, methyl cation, and methyl radical, are shown in Figure 1.1. Ethane is composed of two methyl groups connected by a covalent bond and is a very stable compound. The methyl anion and methyl cation have an ionic bond mainly between carbons and counter ions, respectively, and are not particularly unstable, though there are some rather moisture-sensitive species. However, the methyl radical is an extremely unstable and reactive species, because its octet rule on the carbon is not filled. The carbon atom in the methyl cation adopts sp2 hybridization and the structure is triangular (120°) and planar. The carbon atom in the methyl anion adopts sp3 hybridization and the structure is tetrahedral (109.5°). However, the carbon atom in the methyl radical adopts a middle structure between the methyl cation and the methyl anion, and its pyramidal inversion rapidly occurs as shown in Figure 1.1, even at extremely low temperature. 

The hybridization and bond angles of a simple carbanion also resemble those of an amine. The carbon atom is sp3 hybridized and tetrahedral. One of the tetrahedral positions is occupied by an unshared lone pair of electrons. Figure 4-16 compares the orbital structures and geometry of ammonia and the methyl anion. 

In certain organic compounds, covalent bonds can be so strongly polarized that their structure and reactivity may be approximated by the corresponding ionic formulas. For example, the covalent bonds in methyl triflate 48 and methyllithium 49 are so strongly polarized that they behave as if they were fully ionized compounds, sources of the methyl cation and methyl anion respectively ... 

The microstructure of polymer formed by anionic polymerization of V was analyzed by and NMR spectroscopy. Both and NMR spectra indicate that the methyl groups bonded to silicon may be in one of three distinct environments. 

Each carbon is tetrahedral one has three carbon/hydrogen a single bonds, while the other has only two such bonds and a lone pair. This ion is even less stable than the methyl anion, because there are even more hydrogens that would prefer to donate electrons to the carbon that carries the negative charge. 

However, because there is only one electron in that orbital, it does not have the same repulsive effect as a pair of electrons. As a consequence the carbon/hydrogen bonds are not forced together as much as they are in, for example, the methyl anion, CH3, which adopts an almost regular tetrahedron shape. Suggest the direction and degree of polarisation that is present in the methyl radical. 

Hough and Richardson390 proposed that the loss of 178 from the 2,6-anhydro disulfone 189 occurs by dissociation of the C-l-C-2 bond to give the oxonium ion 190, which would be expected to adopt a conformation approximating the half-chair form illustrated, plus the bis(alkylsulfonyl)methyl anion, which subsequently react with solvent to yield D-lyxose and 178, respectively. In accord391 with this rationalization, (a) the C-methyl homologue (191) of 189 is not de-... 

One other example of alkane oxidative addition to a higher oxidation state late transition metal has been reported by Goldberg. Reaction of the trispyra-zolylborate complex K[r 2-Tp PtMe2] with B(C6F5)3 leads to the abstraction of a methyl anion and the formation of a transient species that adds to the C-H bonds of benzene, pentane, or cyclohexane (Eq. 15). This result provides the first example of the intermolecular addition of a C-H bond to a Ptn species to give a stable PtIV product [71]. Earlier work by Templeton had demonstrated that the trispyrazolylborateplatinumdialkylhydride product would be stable [72]. 

Tris(pentafluorophenyl)borane (35) is a powerful Lewis acid with a hard boron center. It interacts strongly with hard Lewis basic centers and abstracts hard anion such as methyl anion and hydride to initiate selective reactions that are otherwise difficult to achieve. The B(CgF5)3-promoted early transition-metal-catalyzed olefin polymerizations are typical reactions [16]. The B(C6F5)3-Ph3SiH system is useful for hydro-silylation of the carbonyl group, in which the boron of 35 activates the Si—H bond rather than the carbonyl group (see 40 in Scheme 3.39) and reduces even the ester carbonyl group effectively [17]. A number... 

Trimethylsilyl)methyl anion 328 reacts with N20 to generate Me3SiO 329 and the driving force for reaction 128 is obviously the formation of the strong silicon-oxygen bond and the conversion of the highly basic carbanion to the more stable oxide ion 330. 

Bonding in the Methyl Cation, the Methyl Radical, and the Methyl Anion... 

---