How Can You Determine If an Alkyloxonium Ion Will Lose Water Readily?

[chantella28]

I'm working on a number of problems that tells me to write the structure of the alkyloxonium ion produced after an alcohol is protonated by a strong acid

it says that if the alkyloxonium ion is capable of losing water readily, write the structure of the resulting carbocation and if the carbocation obtained is likely to undergo rearrangment write the structures of all new carbocations that could form

i don't have a problem with the protonation of the alcohols, or the rearrangments of a carbocation (it will rearrange to form increasingly stable compounds) but i don't know how to tell when an alkyloxonium ion is cabable of losing water readily... I'm thinking it might have something to do with the position of the water (1°, 2°, 3° carbon) and waters ability as a leaving group, but I'm not sure.

if somebody could give me some pointers on how to tell when it will rearrange, that would be great

 

[GCT]

yes, it has to do with the position of the water, that is the stability of the resulting carbocation as well as the transition state of the compound. If you have a particular case which you wish to work out, than feel free to post the problem.

 

[Blueshift5]

I would suggest looking at the stability of the resulting carbocation and the strength of the acid used for protonation. The more stable the carbocation, the more likely it is to undergo rearrangement. In general, 3° carbocations are more stable than 2° or 1° carbocations, so if the alkyloxonium ion is formed at a 3° carbon, it is more likely to undergo rearrangement. Additionally, stronger acids will protonate alcohols more easily and produce more stable carbocations, increasing the likelihood of rearrangement.

To determine if an alkyloxonium ion is capable of losing water readily, you can look at the stability of the resulting carbocation and the strength of the bond between the oxygen and the carbon. If the bond is weaker, it is more likely to break and release water, forming a carbocation. This can also depend on the nature of the alcohol and the acid used for protonation.

In terms of predicting the structures of new carbocations that could form through rearrangement, you can consider the possible shifts of hydride or alkyl groups, as well as the stability of the resulting carbocation. As mentioned before, 3° carbocations are generally more stable than 2° or 1° carbocations, so shifts that result in a 3° carbocation will be favored.

Overall, predicting the behavior of alkyloxonium ions and carbocations requires an understanding of the principles of acid-base chemistry and carbocation stability. Experimentation and data analysis can also provide valuable insights into the reactivity of these species. I would recommend consulting a textbook or other reliable resources for further information and examples.