Question

Which of the following compounds is most acidic? (Consider the functional groups present and their effect).

Select one:

a. ethanol

b. propanol

c. 2-chloropropanol

d. butanol

e. 3-chloropropanol

Answer 1

The acidity of the following compounds decided by two effects namely:

+I effect and -I effect

So, the groups with +I effect (mostly alkyl groups) tends to decrease the acidity of alcohols beacuse the alkyl group are electron releasing so it increases the electron density on oxygen atom of the alcohol which makes the release of proton difficult. Therefore, the order of acidity in alcohol be like :

CH3OH > 1° alcohol > 2° alcohol > 3° alcohol

And, when the group with -I effect attached to the chain it tends to increase the acidity of alcohols because it pulls the electrons towards itself and thus making oxygen deficient and therefore makes the release of proton easier.

And - I effect is distance dependant ie the more it would be closer to carbon carrying OH group, the more would be the acidity.

So, the order of following compounds in terms of acidity would be :

2-chloropropane > 3-chloropropane > ethanol > propanol > butanol

So, we can see, 2-chloropropane is the most acidic among the given compounds.