Advices For Studying Organic Chemistry

(Wang) #1
Table 3.1 Relative Strength of Selected Acids and their Conjugate Bases

Acid Approximate pKa Conjugate Base


Strongest Acid HSbF 6 (a super acid) < − 12 SbF 6 − Weakest Base


Incr

easing ac

id stre

ngth

HI
H 2 SO 4
HBr
HCl
C 6 H 5 SO 3 H
(CH 3 ) 2 O+H
(CH 3 ) 2 C=O+H
CH 3 O+H 2
H 3 O+
HNO 3
CF 3 CO 2 H
HF
H 2 CO 3
CH 3 CO 2 H
CH 3 COCH 2 COCH 3
NH 4 +
C 6 H 5 OH
HCO 3 −
CH 3 NH 3 +
H 2 O
CH 3 CH 2 OH
(CH 3 ) 3 COH
CH 3 COCH 3
HC≡CH
H 2
NH 3
CH 2 =CH 2

− 10
− 9
− 9
− 7
−6.5
−3.8
−2.9
−2.5
−1.74
−1.4
0.18
3.2
3.7
4.75
9.0
9.2
9.9
10.2
10.6
15.74
16
18
19.2
25
35
38
44

I−
HSO 4 −
Br−
Cl−
C 6 H 5 SO 3 −
(CH 3 ) 2 O
(CH 3 ) 2 C=O
CH 3 OH
H 3 O
HNO 3 −
CF 3 CO 2 −
F−
HCO 3 −
CH 3 CO 2 −
CH 3 COCH−COCH 3
NH 4 +
C 6 H 5 O−
HCO 32 −
CH 3 NH 3
HO−
CH 3 CH 2 O−
(CH− 3 ) 3 CO−
CH 2 COCH 3
HC≡C−
H−
NH 2 −
CH 2 =CH−

Incre

asing base strength

Weakest Acid CH 3 CH 3 50 CH 3 CH 2 − Strongest Base


3.5C PREDICTING THE STRENGTH OF BASES


  1. The stronger the acid, the weaker will be its conjugate base.

  2. The larger the pKa of the conjugate acid, the stronger is the base.

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