Summary
Summary Unit 3.3.4. - Alkenes
- Module
- Unit 3.3.4 - Alkenes
- Institution
- AQA
Detailed revision notes for AQA A Level chemistry - organic - 3.3.4. - mechanisms - polymers - Markovnikov stability rule
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ALKENES3. 3. h I
.
.
STRUCTURE BONDING , REACTIVITY
,
unsaturated hydrocarbons
-
-
bonding : double covalent bond
pairs of
-
two shared e in line between two C
molecular orbital ( high probability of
finding particular pair of e- )
physical properties
only 1. ME Van :
der Waals weak 1. M F
-
-
- .
-
NPT & BPT are similar between the same chain structure alkane and equivalent alkene
-
insoluble in water
Sigma ( 61 bonds
single covalent bond can have
sigma without pi
-
,
can 't have
caused
by end on overlap of electron orbitals pi without sigma
- -
IT bond
pi CHI bond £
formed
by sideways overlap of orbital &
-
-
e
H -
-
-
. .
. '
'
H
A bond
tightly
- . .
not hold
. .
-
e in :
as C -
C
Bad
H H
attracts ( positive end of molecule) ¥03.74
tively charged polar
-
ions
↳ CAUSES ALKENES TO BE FAR MORE REACTIVE THAN ALKANES o bond
, 3.3.42 .
ADDITION REACTIONS OF ALKENES
1.
electrophilic addition
molecule added bond
-
=
liking reagent across
-
electrophile
.
e
pair acceptor
-
e
-
,
attracted dense A bond 6 bond it bond
-
intact
-
to the caused by le
"
e
region in
rearrange
=
;
mechanism : l,
electrophile attracted to =
bond t ion
A bond )
( high density H
-
area H
e
charged ( polar)
-
have ⑦ area ti H l l
, -
④
charged electrophile accepts pair of C C X Y → H C c
-
-
t H
-
-
l
- -
e -
, '
' l l
H
3.
,
a ⑤ ion ( CARBOCATION what electrophile added ) formed
-
-
H
y y
h
,
-0
charged ion forms a bond with carbocation
1. REACTION WITH HYDROGEN HALIDE ① FIBT
reagent hydrogen : bromine Hot Bri
-
H
,
C C
# -
H
Htt
-
-
electrophile
'
:
H
H
-
H H
e
.
Htt attracted to f- Clhigh e
-
density area )
①
H -
C
l
-
l
C -
H
" t
l of H
r
Bromine nucleophile
pairs of e- from f- C forms bond with as
°
°
I
-
!!
'
H
to form ① ion ( CARBOCATION) :L : .
one of Br lone pairs
" +
Brr Brd attacks C
-
-
drawn to
-
•
e in the H -
HETEROlytic Fission H H
( both e- go
to Br ) ③ l l
byproducts
°
no
H -
C -
C -
H
Br attaches to 't of carbocation and forms
-
°
ion : i i
"
when =
not in middle
H Br
bond with one of its pairs of e- Brian bond to either C
CARBOCATION STABILITY
3 structural factors carbon atoms
neighbouring
•
mains :
neighbouring carbon carbon multiple bonds
• -
atoms with lone
neighbouring pairs
•
>
adjacent alkyl groups stabilize carbocation
H CHS
number of carbons H H l
l
① ,
-
attached to carbocation CH , c C C
' ' '
Hf
'
CH, HI CH 3
it
, C CHS
O l 2 3
methyl primary secondary tertiary
least stable
>
most stable
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