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The transition states for SN1 reactions that showcases tertiary carbons have the lowest transition state energy level in SN1 reactions. A tertiary carbocation will maximize the rate of reaction for an SN1 reaction by producing a stable carbocation. This happens because the rate determining step of a SN1 reaction is the formation of the carbocation.
A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH + 3, methanium CH + 5, acylium ions RCO +, and vinyl C ...
The stabilities of the carbocations formed by this dissociation are known to follow the trend tertiary > secondary > primary > methyl. Therefore, since the tertiary carbocation is relatively stable and therefore close in energy to the R-X reactant, then the tertiary transition state will have a structure that is fairly similar to the R-X reactant.
The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols. With primary and secondary alkyl halides, the alternative S N 2 reaction occurs.
One such example is the 1-methyl-1-cyclopentyl cation, which is formed from both the cyclopentane and cyclohexane precursor. In the case of the cyclohexane, the cyclopentyl cation is formed from isomerization of the secondary carbocation to the tertiary, more stable carbocation. Cyclopropylcarbenium ions, alkenyl cations, and arenium cations ...
Although the initial carbocation is already tertiary, the oxygen can stabilize the positive charge much more favorably due to the complete octet configuration at all centers. It can also be seen as the -OH's lone pairs pushing an alkyl group off as seen in the asymmetrical pinacol example.
tertiary cations are stable and many are directly observable in superacid media. The stabilization by alkyl groups is explained by hyperconjugation. [10] The donation of electron density from a β C-H or C-C bond into the unoccupied p orbital of the carbocation (a σ CH/CC → p interaction) allows the positive charge to be delocalized.
The chemical basis for Markovnikov's Rule is the formation of the most stable carbocation during the addition process. Adding the hydrogen ion to one carbon atom in the alkene creates a positive charge on the other carbon, forming a carbocation intermediate.