651.
06
114
Carbocations
terminology: historically, R3C⊕
was referred to as a “carbonium ion” but:
C
vs
C
carbonium carbenium
(hypervalent) (hypovalent)
5 bonds to C -rare 3 bonds to C -commonplace
moot point until the advent of super acids (George Olah,...
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651.
06
114
Carbocations
terminology: historically, R3C⊕
was referred to as a “carbonium ion” but:
C
vs
C
carbonium carbenium
(hypervalent) (hypovalent)
5 bonds to C -rare 3 bonds to C -commonplace
moot point until the advent of super acids (George Olah, Nobel ‘96)
ex:
CH4
FSO3H - SbF5
SO2 (l)
"super acid"
CH5 SbF6 CH3
- H2
(also HF - SbF5)
methanonium
ion extremely non-nucleophilic,
non-basic counterion
(see Olah, JACS 1972, 94, 808; CHEMTECH 1971, 1, 566)
structure:
R
R
R C
empty p orbital
sp2 hybridized
quite standard sp2 hybridization
H
C
HH
H
H
3 - center, 2e- bond
planar structure
note: it lacks an octet ⇒ unstable
What about ?
H
H H
H H
empty sp
2
orbital (very unstable)
-can’t rehybridize to give empty p orbital
Less
