node anti bonding M ( σ* ) A A : bonding M ( σ ) A: atomic orbital M: molecular orbital
node anti bonding M filled orbital of molecular 1 M bonding M vacant orbital of molecular 2 LUM
LUM (lowest unoccupied molecular orbital) 3 3 anti bonding σ* x bonding π' z π' y σ x M (highest occupied molecular orbital) z π z π y σ 's y x σ s
3 3 LUM Eσ * σ* x Eσ σ x p x p x M
2 2 π* z LUM anti bonding bonding π z M π' y π y π x z σ' s y σ s x
2 2 LUM Eπ * π* Eπ π p z p z M
LUM σ* x Eσ * p x Eσ σ x p x M
LUM Eσ * π* Eσ p x π p x M
Ψ 4 π* π* Ψ 3 anti bonding LUM bonding M Ψ 2 π π Ψ 1
LUM (1) M (1) LUM (2) M (2)
Nu (M) π* = (LUM) π = (M) E (LUM)
p orbital axis N M LUM θ axis θ = 109 ( Bürgi-Dunitz angle) M N LUM l axis
M-LUM M-LUM Na + LUM M l - M δ + δ - 2 Br Br 2 LUM
Ψ 1 Ψ 2 hard soft +, + = 3 Si +
cyclooctene trans cis π bond biradical θ θ θ = 0 θ = 90 60 120 120
Bredtʼs rule: (bridgehead) Ph N Me Bz Ac taxol Ac P-263,114 2
2 M π ' ' ' ' σ SP 3 ( ' ' SP 2
1) rotation about single bond ' ' ' synclinal ' antiperiplaner ' < << ' eclipsed gauche staggered (anti) ' E a eclipsed σ - E b σ - Ea + Eb = 0 rule:two-electron interactions are bonding, four-electron interactions are antibonding.
' 3 1,3-diaxial interaction ' 2 1 cis 1 3 ' 1 ' 3 allylic 1,3-strain (A strain) ' 30 '
1,3-diaxial interaction ' ' eq eq α-d-glucose β-d-glucose 1-methyl derivative ax 1,3-diaxial interaction 2 64% eq Me 2 67% 33% Me 36% pentacetyl derivative tetracetyl 1-chloro derivative Ac Ac Ac Ac Ac 2 Ac Ac Ac Ac 86% 14% Ac Ac Ac Ac Ac l 2 Ac Ac Ac 94% 6% Ac l ax electronegative group
σ-delocalisation n-σ* overlap effect anomeric effect n (M) σ* - (LUM) n antiperiplanar σ* - rule: There is a stereoelectronic preference for conformations in which the best donor lone pair is antiperiplanar to the best acceptor bond. antiperiplanar
σ σ σ (M) σ* - (LUM) ' staggered (anti) antiperiplanar rule: There is a stereoelectronic preference for conformations in which the best donor σ bond is antiperiplanar to the best acceptor bond. M: n N > n > σ -, σ - >> σ -N > σ - > σ -S > σ -hal LUM: π* = > σ* -hal > σ* - > σ* -N > σ* -, σ* -
F F staggered (anti) repulsion? F F gauche F F σ - -σ* -F interaction σ (M) F σ* -F (LUM)
Karplis 3 J 1,2 θ θ θ 0 θ = 0 θ = 90 θ = 180 σ - (M) σ* - (LUM) σ - (M) σ* - (LUM)
I. 1) S N 1 reaction of haloalkane + - 1 cation 3 cation << 3 << 3 hyperconjugation 3? σ (M) vacant P (LUM)
α Me l Me l - Me hyperconjugation n (M) vacant P (LUM)
3) reactivity and regioselectivity for the Friedel-rafts reaction Me Me Me - Me Me o p hyperconjugation n (M) Me vacant P (LUM) Ac
σ-σ* interaction short F long NMe 3 F S + NMe 3 F NMe 3 trifluoromethoxide F F F F n -σ* -F hyperconjugation σ* -F (LUM) F F F n (M)
' N 3 3 N ' N n N σ* - axis N ' ' - - N ' N ' N '
S Me S Me S S Me Me S 2 Ar S 2 Ar S 2 Ar S 2 Ar Ar 2 S S Me Ar 2 S S
exo endo Y 6-exo-tet Y 6-endo-tet θ θ = 180 tet (SP 3 ) θ = 109 θ trig (SP 2 ) θ = 60 θ trig (SP 2 )
Me N 5-endo-trig Me endo N 2 exo Me N 2 5-exo-trig N Me 2 Me 3 Na Ph 5-endo-dig Ph Ph
(1) (2) n l σ* -l l fast Br fast slow Br Br twist boat chair (1) (2) a b Br Br chair Br endo exo a b 6-endo-tet 5-exo-tet exo? twist boat
S N 2 (1) M/LUM M Y LUM Y π = (M) π = (LUM) Y Y Y Y n (M) Me 2 NPh Br N + Me 2 Ph Y Y Br N + Me 100 times faster!! 2 Ph
S N 2 (2) S + NS S NS Bn S + Bn S NS NS S + NS S NS-Et 8000 times slower!! S + S + NS NS
S N 1 (1) π = n S N 1 S N 2 π = n π = vacant
S N 1 (2) σ =,, metal ( σ delocalization σ p
Si E + Si E E Si E a Si E Si E + a b E + b Si E
σ-delocalisation Involving - bond (1) σ - σ cyclopropane cyclopropane π* = π* = cf.
σ-delocalisation Involving - bond (2) a l 2 a a b b b
σ-delocalisation Involving - bond throuh the space the center of electron-density 2 N
MgBr 2 2 M MgBr LUM σ -M (M) M Br σ* Br-Br (LUM) Br
(t-bu 2 ) 3 Sn Et Me Br 2 Br Et Me Et Me Br retention inversion σ -M (M) Sn Br σ* Br-Br (LUM) Br σ -M (M) Sn Br Br σ* Br-Br (LUM) retention inversion
1) (1) Nu Nu Nu M Nu Nu 109 2 1 π* = (LUM) Nu 1 2 Nu β-attack α-attack β α Nu * 2 1 * 2 Nu 1
(1) t-bu t-bu t-bu α- β- Li(sec-Bu) 3 B 97 : 3 NaB 4 14 : 86 bulky t-bu 1,3-diaxial interaction
α σ Nu β-attack? α-attack σ* - (LUM) Nu 2 2 1 1 α-attack? Nu Nu M ram (Felkin-Anh ) Nu S 109 M L Felkin-Anh model Nu S L L S Nu M chlation model
Nu Nu Nu β-attack twist boat + Nu α-attack Nu Nu chair
-Y Y σ* Br-Br (LUM) Br Br Br Br Br Br Br Br π = (M) Br Br σ* - (LUM) + π = (M)
Y + Y M n π = σ - p σ -Si Si
π Z -Y Z Y Z β-face π = (M) E α-face σ -Z Z Z: electron donating group Z 1 2 -Y Z * * 2 1 Y 1 2 Z Allylic 1,3-strain β-face 1 2 Z 30 1,2-strain 2 1 Z 2 120 Z 30 90 1
π t-bu trans SiMe 3 Ph t-bul, Til Me Ph 4 Me Ph t-bu σ -Si Si cis SiMe 3 Ph t-bu t-bul, Til S Ph 4 Ph t-bu Me σ -Si Me Si
π emote ontrol by F atom F σ - σ* - "" mpba F F ( 2 : 1 ) Z-isomer E-isomer
Me S Me S Me S Me S Me S σ* -S S S S Me S S Z-enolate Z-enolate Me S σ* -S 1,4-addition Me S Me S "syn-isomer" π π
β Elimination 1) E1 - + cation intermadiate 2) E2 B - B + 3) E1cB B B + -
2) E2 - + σ - (M) vacant P (LUM) σ - (M) - σ* - (LUM) B + NMe 3 NMe 3 NMe 3 NMe 3 anti: 95% Me 3 N NMe3 anti : syn = 54 : 46 σ - (M) σ* - (LUM) syn: 90% synperiplaner
NMe 3 NMe 2 92% 8% Me N Me Me S N 2 100% NMe 2
Me Me Br Br σ σ* σ σ* σ σ* σ σ* 30 60 Sp 3 anti Sp 3 syn Sp 2 anti Sp 2 syn
2 2 Ms tert-bu Ms
N N 2 / N Ts N l N 2 N N Me Ts N Me
1,2-shift σ 1 2 σ* antiperiplaner Pinacol earrangement 2 antiperiplaner 2 3 3 antiperiplaner 3 3 2 3 3 3 3 3 3
Beckman earrangement Ar σ Me N Me N σ* Ts Ar 2 Me N Ar antiperiplaner ofman earrangement Ar N NaBr Na Ar σ N σ* Br N Ar 2 N Ar antiperiplaner
σ σ LUM: π* = > σ* -hal > σ* - > σ* -N n (M) σ* - (LUM) σ (M) σ* - (LUM) antiperiplanar