Mutarotation

Question 1

glucose interconverts

Answer 1

beta glucose in base or acid converts to alpha glucose

with base ring opens, bond rotates, and ring reforms

in acid protonate ether, C1OH db forms opens ring

Question 2

alpha and beta glucose…

Answer 2

are stereoisomers called diastereomers
called aromers

c1 carbon called anomeric carbon

in equilibrium there is 36% alpha and 64% beta

Question 3

anomeric effect

Answer 3

heteroatomic substituent on C1 prefers axial position

67% alpha 33% beta

Question 4

electrostatic model

Answer 4

in beta dipoles are cumulative (less stable)

in alpha dipoles cancel which reduces charge repulsion

Question 5

molecular orbital theory

Answer 5

favorable orbital overlap between unpaired e- on ring O and antibonding MO of C1-X bond

antiperiplanar in alpha

Question 6

mutarotation vs CH3OH rxn

Answer 6

muta 64% beta CH3OH 33% beta

solvent polarity is the cause!

as polarity decreases, C1 axial&raquo_space; C1 equitorial

Question 7

solvent polarity

Answer 7

more polar solvent interacts with net dipole of beta to stabilize: more beta

less polar solvent increases anomeric effect: more alpha

Question 8

CH3OH rxn

Answer 8

glucose + HCl, CH3OH protonate C1 OH

H2O leaves, ether lone pair double bonds carbocat

CH3OH atks C1, Cl- deprotonates