# Negative charged intermediate in acidic conditions - what's the problem?

Why positively charged intermediates are preferred over negative charged intermediates, when formed during a reaction taking place in acidic conditions?

For example:

Image source: Organic Chemistry by David R. Klein

Here, per Organic Chemistry by David R. Klein says,

That is, the mechanism does not exhibit any negative charges, which is consistent with acidic conditions.

Why?

• What do you think happens to negatively charged species under acidic conditions? – orthocresol Jan 2 '17 at 17:42
• What happens to a positively charged one? I am missing somewhere. – Reeshabh Ranjan Jan 2 '17 at 17:55
• Well, cations containing hydrogen are usually quite acidic and anions basic, aren't they? – Mithoron Jan 2 '17 at 19:55

$$\ce{HA + H2O <=> H3O+ + A-}\tag{1}$$
However, this does not mean that no anions can exist in aquaeous solution. For example, a typical method to transform alcohols into iodides is refluxing in aquaeous hydrogen iodide. Here, $\ce{HI}$ is a very strong acid that very readily dissociates to give iodide anions, $\ce{I-}$. These, even though negatively charged, do exist in acidic conditions and are able to attack nucleophilicly. That’s all due to the high acidity of $\ce{HI}$.
$$\ce{R-OH + H3O+ + I- <<=> R-OH2+ + H2O + I- -> R-I + 2 H2O}\tag{2}$$