Ch_322b_20.03

Ch_322b_20.03 - Basicity of Amines: Amine Salts Amines are...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Basicity of Amines: Amine Salts Amines are relatively weak bases. They are stronger bases than water and alcohols, but weaker bases than hydroxide and alkoxide ions and most carbanions. relative base strength R-O: H : < R-N-R'' R' < R-O - < R-C-R'' R' - A Quantitative Description of Base Strength The strength of a base is defined by the equilibrium: RNH 2 + H 2 O RNH 3 + + HO - K eq For dilute solutions, the concentration of the water does not change and a basicity constant (K b ) is defined as K b = K eq [H 2 O] = [RNH 3 + ] [HO - ] [RNH 2 ]
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Conjugate Pairs Tables often list the acidity constants, K a , of the conjugate acids. Remember that RNH 2 and RNH 3 + are conjugate pairs . RNH 2 : + H 2 O RNH 3 + + HO - base conjugate acid The defining equilibrium for acid strength of the conjugate acid is RNH 3 + + H 2 O K eq ' RNH 2 + H 3 O + and the acidity constant of the conjugate acid is given as K a = K eq [H 2 O] = [RNH 3 + ] [RNH 2 ] [H 3 O + ] ' Since for conjugate pairs, K a x K b = K w (1.0 x 10 -14 ) it is possible to determine the strength of a base from the acidity constant of the conjugate acid.
Background image of page 2
Estimating Base Strength from pK a Values It follows that strong bases (large values for K b ) have weak conjugate acids, and weak bases have strong conjugate acids. Some Examples of Bases with pK
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 11

Ch_322b_20.03 - Basicity of Amines: Amine Salts Amines are...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online