Question

Which of the following is the strongest base? CH3CH2OH CH3CH2O- CF3CH2O- CH3CH2S- CH3CH2NH- Please explain. I can't find anything on this and I would really like to know how to determine this. Thanks!

Answer 1

CH₃CH₂OH. CH₃CH₂O^- CF₃CH₂O^- CH₃CH₂S^- CH₃CH₂NH^-

We all know that acidity of a molecule depends upon the donating the protons and basicity depends upon accepting the proton.

Ability to donate proton can be evaluated by Ka value. So more the Ka value more the acidic nature. Negative logarithm of Ka is pKa. So less the pKa value more acidic in nature.

More the pKa value more basic in nature.

pKa value of ethanol is 15.9 and its conjugate base is ethoxide

pKa value of CF₃ CH₂OH is 12.4 and its conjugate base is CF₃CH₂O^-

pKa value of CH₃CH₂SH is. 10.6 and its conjugate base is CH₃CH₂S^-

pKa value of CH₃CH₂NH₂ is 35 and its conjugate base is CH₃CH₂NH^-

Among the above molecules order of acidity is

thioethanol > trifloroethanol > ethanol > ethyl amine

So order of basicity of their conjugate base reverse of above order because weaker the acid stronger its conjugate base

So, CH₃CH₂NH^-> C₂H₅O^-> CF₃CH₂O^->C₂H₅S^-> C₂H₅OH

So strongest base is CH₃CH₂N^- and hydrogen is hard to remove from the compound. So it is ready to accept the proton than to donate