Carbocations methyl

Unlike tertiary and secondary carbocations methyl and primary carbocations are too high m energy to be intermediates m chemical reactions However methyl and primary... 

Secondary alkyl halides react by a similar mechanism involving attack on benzene by a secondary carbocation Methyl and ethyl halides do not form carbocations when treated with aluminum chloride but do alkylate benzene under Friedel-Crafts conditions The aluminum chloride complexes of methyl and ethyl halides contain highly polarized carbon-halogen bonds and these complexes are the electrophilic species that react with benzene... 

Substrate 3° (requires formation of a relatively stable carbocation) Methyl > 1° > 2° (requires unhindered substrate)... 

Substituent effects Carbocations are formed in the S l reactions. The more stable the carbocation, the faster it is formed. Thus, the rate depends on carbocation stability, since alkyl groups are known to stabilize carbocations through inductive effects and hyperconjugation (see Section 5.2.1). The reactivities of SnI reachons decrease in the order of 3° carbocation > 2° carbocation > 1° carbocation > methyl cation. Primary carbocation and methyl cation are so unstable that primary alkyl halide and methyl halide do not undergo SnI reachons. This is the opposite of Sn2 reactivity. 

Methyl cation, 105, see also Carbocations Methyl chloride... 

Unlike tertiary and secondary carbocations, methyl and primary carbocations are too high in energy to be intermediates in chemical reactions. However, methyl and primary alcohols are converted, albeit rather slowly, to alkyl halides on treatment with hydrogen halides. Therefore, they must follow a different meehanism, one that avoids carbocation intermediates. This alternative process is outlined in Mechanism 4.2 for the reaction of 1-heptanol with hydrogen bromide. 

Butyl carbocation Methyl 2-Propyl carbocation Ethyl... 

From experiments such as these and a great amount of other experimental evidence, we know that a 3° carbocation is more stable and requires a lower activation energy for its formation than a 2° carbocation. A T carbocation, in turn, is more stable and requires a lower activation energy for its formation than a 1 ° carbocation. Methyl and 1° carbocations are so unstable they are rarely observed in solution. It follows, then, that a more stable carbocation intermediate forms faster than a less stable carbocation intermediate. Following is the order of stability of four types of alkyl carbocations. 

The structures, geometries, and relative stabilities of simple alkyl radicals are similar to those of alkyl carbocations. Methyl radical is planar, and all other radicals are nearly so, with bond angles near 120° about the carbon with the unpaired electron. This geometry indicates that carbon is sp hybridized and that the unpaired electron occupies the unhybridized 2p orbital. As mentioned, the order of stability of allyl radicals, like alkyl carbocations, is 3° > 2° > 1° methyl. 

---