The general tendency of anomeric substituents to prefer an axial position is called Anomeric effect.
For example, the α-methyl glucoside is more stable than the β-methyl glucoside due to hyperconjugation.
In α-methyl glucoside, the non bonding HOMO with a pair of electrons on the ring oxygen is antiperiplanar to the antibonding LUMO of C-O bond in methoxy group. This allows hyperconjugation between them and thus by stabilizing the α-form. HOMO - highest occupied molecular orbital LUMO - lowest unoccupied molecular orbital
The general tendency of anomeric substituents to prefer an axial position is called Anomeric effect.
For example, the α-methyl glucoside is more stable than the β-methyl glucoside due to hyperconjugation.
In α-methyl glucoside, the non bonding HOMO with a pair of electrons on the ring oxygen is antiperiplanar to the antibonding LUMO of C-O bond in methoxy group. This allows hyperconjugation between them and thus by stabilizing the α-form. HOMO - highest occupied molecular orbital LUMO - lowest unoccupied molecular orbital
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ReplyDeletethis conformation is more stable since lone pairs on ether oxygen in ring are anti to glycosidic bond that interacts via hyperconjugation
DeleteThe general tendency of anomeric substituents to prefer an axial position is called Anomeric effect.
DeleteFor example, the α-methyl glucoside is more stable than the β-methyl glucoside due to hyperconjugation.
In α-methyl glucoside, the non bonding HOMO with a pair of electrons on the ring oxygen is antiperiplanar to the antibonding LUMO of C-O bond in methoxy group. This allows hyperconjugation between them and thus by stabilizing the α-form.
HOMO - highest occupied molecular orbital
LUMO - lowest unoccupied molecular orbital
how can we tell that alpha-glycoside is a major product??
ReplyDeletethis conformation is more stable since lone pairs on ether oxygen in ring are anti to
ReplyDeleteglycosidic bond that interacts via hyperconjugation
The general tendency of anomeric substituents to prefer an axial position is called Anomeric effect.
ReplyDeleteFor example, the α-methyl glucoside is more stable than the β-methyl glucoside due to hyperconjugation.
In α-methyl glucoside, the non bonding HOMO with a pair of electrons on the ring oxygen is antiperiplanar to the antibonding LUMO of C-O bond in methoxy group. This allows hyperconjugation between them and thus by stabilizing the α-form.
HOMO - highest occupied molecular orbital
LUMO - lowest unoccupied molecular orbital