Planar methyl group

The orbitals of a planar methyl group, created using the rules of Table 1.7. 

The importance of steric effects in determining the oxidation state of the product can be illustrated by a thioether linkage, eg (57). If a methyl group is forced to be adjacent to the sulfur bond, the planarity required for efficient electron donation by unshared electrons is prevented and oxidation is not observed (48). Similar chemistry is observed in the addition of organic nitrogen and oxygen nucleophiles as well as inorganic anions. 

Though it could be argued that a planar structure analogous to 11 for acetyl chloride would be disfavored by steric crowding between the chlorines and the methyl group, this was not found to... 

The crystal structure of a CODH/ACS enzyme was reported only in 2002.43,44 It reveals a trio of Fe, Ni, and Cu at the active site (6). The Cu is linked to the Ni atom through two cysteine-S, the Ni being square planar with two terminal amide ligands. Planarity and amide coordination bear some resemblance to the Ni porphinoid in MCR. A two-metal ion mechanism is likely for acetyl CoA synthesis, in which a Ni-bound methyl group attacks an adjacent Cu—CO fragment with formation of a Cu-acyl intermediate. A methylnickel species in CODH/ACS has been identified by resonance Raman spectroscopy.45... 

The solid-state structure of 68c, Figure 36, shows that the zinc atom is surrounded in a trigonal-planar fashion by one methyl group and two 2,4,6-trisilacyclohexyl ligands, of which one has a chair conformation, while the other one has a boat conformation. 

However, such intercalation involves the insertion of a flat molecule, with a ir-electron system, between the ir-electron systems of the bases of DNA. Therefore a buckled molecule and/or a methyl group will not fit well in such an intercalation mode. Thus, since the buckled molecules (with a methyl group in the bay region) are more carcinogenic, we concluded that complete intercalation of the hydrocarbon between the bases of DNA is not a likely mechanism for carcinogenicity, since the less planar molecules are more active in terms of carcinogenic activity. However, as we shall show later, it is possible that the planar portion of the PAH may lie between the bases of DNA in a semi-intercalation mode the methyl groups, if present, probably do not take part in this semi-intercalation. 

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