# What is the reason that tertiary alcohol pKa is higher than primary alcohol pKa?

A tertiary alcohol has a $\mathrm{p}K_\mathrm{a}$ of 18 while a primary alcohol has a $\mathrm{p}K_\mathrm{a}$ of 16. Shouldn't the tertiary alcohol be more acidic since its conjugate base is more stabilized due to induction?

• Which tertiary and primary alcohol are you referring to? Please give some references for your data. – bon Apr 30 '15 at 21:03
• I meant (CH3)3COH for tertiary and CH3CH2OH for primary. – Jordan Chan Apr 30 '15 at 21:07
• It's other way around with induction - tert-butyl group is electron donating stronger than ethyl. – Mithoron Apr 30 '15 at 21:55
• Here is a nice explanation. Considering polarizability and solvation effects you can explain the solution pKa data, as well as why it reverses in the gas phase. – ron May 1 '15 at 16:59
• Methanol is a weaker acid than t-BuOH in the gas phase. pubs.acs.org/doi/pdf/10.1021/ja00723a029 – user55119 Dec 6 '17 at 19:41

1. The hydroxy group of the tert butyl alcohol is intramolecular stabilized by hydrogen bonds (2nd image), between the methyl hydrogens and the oxygen. In the other hand, i.e. the hydroxy group of methanol is intermolecular stabilized with another methanol molecules ("Behave more like a water") (3th image). Therefore, the equilibrium $\ce{ROH}\rightleftharpoons\ce{RO^-}+\ce{H^+}$ is more displaced to the right with the methanol than with the tert-butil alcohol.