Undergraduate Organic Chemistry
1. Thorpe-Ingold effect - 5 More substituted chains react faster (e.g. epoxidation)
points
H: More substituted carbon chains decrease the heteroatoms
bond angle which makes it closer to the 102 degree "banana"
angle in an epoxide
H: R/R bond angle increases upon epoxidation which decreases
torsional/steric strain
S: bulky R groups greatly increased the population of reactive
(antiperiplanar) conformations
Transition state stabilisation due to inductive electron donating
effects
2. Baldwin's Rules Modes of Cyclisation:
Exo: bond breaking outside the forming ring
Endo: bond breaking inside the forming ring
Classification of Attack Site:
TET: sp3
TRIG: sp2
DIG: sp
Generally: All exo-tet and exo-trig favoured
Exo generally favoured over endo
5-exo usually fastest and product determining
Enolates:
Enolendo-exo: enolate forming inside the ring
Enolexo-exo: enolate forming outside the ring
3.
, Undergraduate Organic Chemistry
Woodward-Hoffman rules A ground state pericyclic reaction is symmetry allowed when the
- Definition total number of (4q+2)s and (4r)a components is odd
- [4,2] - Diels-alder Cycloaddi-
tion A pericyclic change in the first electronically excited state is sym-
- Electrocyclic ring opening metry allowed when the total number of (4q+2)s and (4r)a com-
of cyclobutene ponents is even
- Claisen Rearrangement
s=suprafacial - bond formation on same sides
(stereochem)
a=antrafacial - bond formation on opposite sides
- Group transfer (S-O ylid
with adjascent alkene)
- [2,2] Ketene cycloaddition
- oxyallyl cation cycloaddi-
tion (cyclopropanone)
- Allyl cation-diene cycloaddi-
tion
- Allyl anion-alkene cycload-
dition and cycloreversion
- 1,3-dipolar cycloaddi-
tion (ozonolysis, azomethine
ylid)
- Chelotropic cycloaddition
(CCl2 carbene, SO2-diene
with rev.)
- Electrocyclic reaction of cy-
cloproyl halide ionization
- Electrocyclic ring opening
of cyclohexadiene
- 1,n Hydride Shifts: [1,5],
[1,7]
- 1,n Alkyl Shifts: [1,2], [1,3]
(stereochem), [1,5] (stere-
, Undergraduate Organic Chemistry
ochem)
- [2,3]-Wittig rearrangement
4. Aldol reaction selectivty cyclic chair-like t.state
(zimmer-man traxler) - using Boron enolate more selective due to shorter B-O bond vs Li-O =>
LDA or Bu2OTf + i-Pr2NEt tighter, more sterically controlled transition state
5. Gauche Effect gauche preference of difluoroethane due to strong stereoelec-
tronic effect of C-H donation into very low energy C-F antibonding
orbital
6. Anomeric Effect stabilisation due to high energy lone pair donation into very low
energy C-X antibonding orbital, therefore partial Pi character and
shorter C-X bond length
7. Primary and Secondary Ki- 1st: D-C has a lower ZPE than H-C (quantum energy levels) there-
netic Isotope Effect fore H-C has a lower activation energy therefore reacts faster
2nd: isotopically varying atom is not part of a bond being bro-
ken, usually observed when it's on a reaction site that changes
hybridization
sp3 to sp2 is faster for lighter isotopes
changing hybridization affects the normal modes thereby chang-
ing the zero point energy
8. draw: cis/trans decalin,
anomeric effect for a
spiroketal
9. Nucleophilic Addition to Car- Steric Arguement: Felkin-Anh
bonyl Stereocontrol (steric, Largest substituent at 90 degrees to carbonyl this leads to 2
EWG, metal ion) conformers
Nucleophile attacks at Burgi-dunitz angle
This leads to 2 possible attacks across either small or medium
1. Thorpe-Ingold effect - 5 More substituted chains react faster (e.g. epoxidation)
points
H: More substituted carbon chains decrease the heteroatoms
bond angle which makes it closer to the 102 degree "banana"
angle in an epoxide
H: R/R bond angle increases upon epoxidation which decreases
torsional/steric strain
S: bulky R groups greatly increased the population of reactive
(antiperiplanar) conformations
Transition state stabilisation due to inductive electron donating
effects
2. Baldwin's Rules Modes of Cyclisation:
Exo: bond breaking outside the forming ring
Endo: bond breaking inside the forming ring
Classification of Attack Site:
TET: sp3
TRIG: sp2
DIG: sp
Generally: All exo-tet and exo-trig favoured
Exo generally favoured over endo
5-exo usually fastest and product determining
Enolates:
Enolendo-exo: enolate forming inside the ring
Enolexo-exo: enolate forming outside the ring
3.
, Undergraduate Organic Chemistry
Woodward-Hoffman rules A ground state pericyclic reaction is symmetry allowed when the
- Definition total number of (4q+2)s and (4r)a components is odd
- [4,2] - Diels-alder Cycloaddi-
tion A pericyclic change in the first electronically excited state is sym-
- Electrocyclic ring opening metry allowed when the total number of (4q+2)s and (4r)a com-
of cyclobutene ponents is even
- Claisen Rearrangement
s=suprafacial - bond formation on same sides
(stereochem)
a=antrafacial - bond formation on opposite sides
- Group transfer (S-O ylid
with adjascent alkene)
- [2,2] Ketene cycloaddition
- oxyallyl cation cycloaddi-
tion (cyclopropanone)
- Allyl cation-diene cycloaddi-
tion
- Allyl anion-alkene cycload-
dition and cycloreversion
- 1,3-dipolar cycloaddi-
tion (ozonolysis, azomethine
ylid)
- Chelotropic cycloaddition
(CCl2 carbene, SO2-diene
with rev.)
- Electrocyclic reaction of cy-
cloproyl halide ionization
- Electrocyclic ring opening
of cyclohexadiene
- 1,n Hydride Shifts: [1,5],
[1,7]
- 1,n Alkyl Shifts: [1,2], [1,3]
(stereochem), [1,5] (stere-
, Undergraduate Organic Chemistry
ochem)
- [2,3]-Wittig rearrangement
4. Aldol reaction selectivty cyclic chair-like t.state
(zimmer-man traxler) - using Boron enolate more selective due to shorter B-O bond vs Li-O =>
LDA or Bu2OTf + i-Pr2NEt tighter, more sterically controlled transition state
5. Gauche Effect gauche preference of difluoroethane due to strong stereoelec-
tronic effect of C-H donation into very low energy C-F antibonding
orbital
6. Anomeric Effect stabilisation due to high energy lone pair donation into very low
energy C-X antibonding orbital, therefore partial Pi character and
shorter C-X bond length
7. Primary and Secondary Ki- 1st: D-C has a lower ZPE than H-C (quantum energy levels) there-
netic Isotope Effect fore H-C has a lower activation energy therefore reacts faster
2nd: isotopically varying atom is not part of a bond being bro-
ken, usually observed when it's on a reaction site that changes
hybridization
sp3 to sp2 is faster for lighter isotopes
changing hybridization affects the normal modes thereby chang-
ing the zero point energy
8. draw: cis/trans decalin,
anomeric effect for a
spiroketal
9. Nucleophilic Addition to Car- Steric Arguement: Felkin-Anh
bonyl Stereocontrol (steric, Largest substituent at 90 degrees to carbonyl this leads to 2
EWG, metal ion) conformers
Nucleophile attacks at Burgi-dunitz angle
This leads to 2 possible attacks across either small or medium
