the sn bond breaking is bond for f ft iii
TRANSCRIPT
Products
The SN2 Mechanism
Summary:
Regiochemistry:
Stereochemistry:
Example:
NaN3
H O + BrC
H
H
H
Transition state
Na
I
Bond that
Bondthatis is breaking
for
storeH f
u ft IiiNucleophile must react at
he back of the C Br bond
this angle and direction ofattack helps break the C Br bond
itH C HTheconfiguration
at C isinverted
BAt
The nucleophile attacks by makinga new bond to C from the back of theC X bond just as the X leaves
N AINVERSION at siteofreactors
4 Inde.phN3ueaEfsP
Products
The E2 Mechanism
Summary:
Regiochemistry:
Stereochemistry:
Example:
NaOH
H3C O + C
H
H
H
Transition state
Na
H3C
CH3
C
Br
CH3
CH3
ClCH3
BondsbeingBonds being
broke
EoutEBr
GHK
43kH H RCH3
C F CCH
The H that is leaving and
the Br must be HK I H B.inanti periplanar
Base removes an H atom as a piband forms and the Br atom leaves
The H and Dr must be
anti peri planarZaitsev's Rule most stable alkene productDetermined by anti periplanar transition state
1734 5 3
µH kHz
Products
The SN1 and E1 Mechanisms
C
Cl
C
H
H
H
C
C
H HH
H
H
C
H
H
H
H3C O H
Products
H3C O HE1 H3C O H
SN1
Summary:
Regiochemistry:
Stereochemistry:
Example:
CH3CH2OH
(S)
Br
H heat
yHaloalkae with CHz 17
Breaka bond
t H tcH3
it.it oE'it fifth city1 H f lH H K H H L Ha t t Make a 11 H
bond it
Take a Take a protonproton awayaway
KE't it H H a inH H d d c C HH C c I l l H
y H H H C HH it if I
t t Hy F HHFor sterically hindered haloalkanes the C X
bond breaks to give a carbocation intermediate thateither reacts as an electrophile Sv 1 or
has a proton taken away EI
EI Zaitsev's RuleSv1 Scrambled not quite I exactly
fr E't sit3 I A4 v Bocage atCHS
To
Substitution/Elimination Decision Map
Primary Haloalkane
Methyl Halide
Tertiary Haloalkane
E2
SN1/E1Very Weak Base ?
SN2
tBuOK ? Yes E2
No SN2
Yes
No
For SN2 Remember Chiral Center InVERSiONFor E2 Remember anti-periplanar and ZaitsevFor SN1 Remember Chiral Center ScramblingFor E1 Remember Zaitsev
Note: With Very Weak Bases, SN2 can compete here, but for the purposes of this class, assume SN1 / E1 predominate
Note: If tBuOK is the very strong base, an appreciable amount of a non-Zaitsev product can be formed because the bulky tBuOK will tend to react with the most accessible H atom.
Secondary Haloalkane
or
Allylic/Benzylic Halides
SN1/E1Very Weak Base ? Yes
Very Strong Base ? Yes E2
No SN2
*
**
*
**
1 Methyl halo alkane always SNZ
2 to halo alkanes Sw 2 with all but
tBu0 k
Kota
try zNEE bond
Sir
nBr I
3 20 halo alkanes Sir 2 with allbut strong bases or veryweak bases
EZ with strong bases
sv1 E1 with very weak bases
strong base
CH CX t CH CE H
Br E220 haloalkane 2,523daLt
Rj 9 INVERSION
very weak base
Nap A Bratz
SNHEI Et NZeitz
SNI
4 30 halo alkanes EZ withall but veryweak bases
Na OH 41700
I Na
EL
Zaitsev
very weak base 1I HOTISNI EI SNIEI
EPIC NEW REACTIOND Alkylation of terminal attkyane
anim with a primary halotaldkane
T P CHz CEC CHICHICHCH C t CH CHIK B.ir
Pr kae 3
New C C bond
Making new GC bonds allows us to
construct larger molecules fromsmaller fragments
Tine capsuleThis is an SNLreaction The halo alkanemust be primary toavoid E3
E Conversion o
vicinal dihalo a Kane
to an alkyne in base
ratio ofmolecules
toBr Br 2 equivalents
NaN H2Hsc CHz H C CEC CH
H H Very straybase Alkyne
Vicinal dihaloalkane
isa E'EIII
When creating a terminal alkyneyou need to all 3 equivalents of
NaN Hz then in a second step addmild acid Halite
For highly substituted halo alkanes
you must first look for t Zaitsev
most substituted alkene productthen possibly rotate
a C C bond to find theanti periplanar geometry that
predicts Evs Z
424 H3 CHIH s
Hye Ia Br D Br CH
E Ciotat H EI'tperiplanor
Not a reactiveconformation
Rotak central C C bondBr
HSE 1B't H C featsHzcHfac C CH HGH tH3
CHIH HH
Br and H are
anti periplanarThis is the reactiveconformation
HE Mr NaOCH Itsy 4 3
HZCHIAE.ec C C c
if bi HEH EZ HE KICKS
Anti perilanarZ product
H IHy H it
E teaHtt
These twoaxons
are These two H atomsa
ratare anti periplanarto the Br atomso they could react
No E2This reactsbecause there
are NO because thereare
anti peri planar anti periplananH atoms H atoms
Thg Ei7z