Methylation of glucose (mechanism)

[duchuy]

Homework Statement

Nucleophilic or electrophilic substitution

Relevant Equations

x

Hi,
I don't understand why this correction would be a nucleophile substitution?
From what understand : The O atoms in the cyclic glucose acts as nucleophiles. ICH3 is also a nucleophile due to the presence of iodine's "non bonding electron pairs" (sorry I don't know the right term for this), and since I is a halogen, CH3 bares partial positive charge.
Ch3 being electrophilic, comes and replace H. So why isn't it a electrophile substitution?
Can you please explain to me what went wrong in my thought process?
And do you have a way that which I can determine what kind of substitution it is everytime because I don't really know which molecule would be the one that that has a substituted group? Like from this case, is H substituted by CH3 or I substituted by glucose?
Thank you so much for your help!

 

[mjc123]

In a sense it's all the same, because you can't have nucleophiles without electrophiles, just as you can't have acid without base, or oxidation without reduction. But in organic chemistry, we think of the reaction occurring at the carbon substrate. Thus, while the above reaction could be seen as an electrophilic substitution of H by methyl at the O of glucose, it would be normal to think of it as a nucleophilic substitution at the C of CH₃I.

 

[duchuy]

thank you sir!