Question

I don't understand this at all, how can you determine the strength of conjugate base by looking at these molecules? How would you determine conjugate acid if that was the question?

7) What is the order of increasing strength of the conjugate base in the following molecules? Cl Cl

Answer 1

An alcohol behaves as an acid by formation of alkoxide ion,

R-OH → RO^​- + H⁺

​The acidity of alcohol is higher when the O-H bond is more polar. Presence of an electron releasing group like halogen increases the polarity of O-H bond​ due to -I effect. Closer the halogen to the C-OH bond, greater is the -I effect. Also -I effect increases with in number of halogen substituents.

Therefore the increasing order of acidic strength would be:

III<II<IV<I

III will be least acidic due to steric hindrance caused by presence of bulky Cl atoms on the same carbon.

We must consider steric reasons and inductive effect while determininng the correct order.