Stereoelectronics Flashcards
why can’t C=C rotate?
p-orbitals are parallel
orbital distortion in C=O bond
O = more electronegative than C
π orbital = distorted to O
π* orbital = distorted to C (opposite)
interaction of adjacent orbitals
adjacent orbitals are able to interact
lowers overall energy (i.e. it’s beneficial)
filled orbital able to donate into unfilled orbital
adjacent orbitals in amide
nitrogen = sp2 hybridised
remaining p orbital is well positioned to overlap with unfilled π* orbital of C=O
Nn (donator) -> π* C=O
*n = non-bonding
x-ray evidence for orbital interaction
C=O bond in amide is longer than in ketone (weaker due to partial filling of π*)
C-N bond in amide is shorter than normal C-N (stronger as it has some double bond character)
orbital interaction in ester
No -> π* C=O
why is the s-trans conformation in esters more stable?
an additional orbital interaction is possible
= 2nd oxygen lone pair in sp2 with σ* of C=O
why are lactones more reactive than esters?
ring locks conformation as s-cis, making it less stable
in sub. cyclohexanes, when is the conformer most stable?
when sub. is placed equatorially
6-membered rings containing oxygen
if carbon adjacent to oxygen has electronegative sub. AXIAL = preferred
epimer
carbohydrates that differ in the location of the -OH group in one location
anomeric effect
tendency of heteroatomic sub. adjacent to a heteroatom in cyclohexane ring to prefer the axial position instead of the less-hindered equatorial
due to No -> σ* C-O (more of these interactions = more stable)
orbital effects in Sn1
[via carbocation]
more stabilising orbital effects = faster reaction
hyperconjugation
donation from σC-C / C-H to empty p-orbital on carbon
conjugation
pi systems linking
