[newbie!]

i have 2 questions regarding pyridine and related compound.
based on:



1) expalin the regiochemistry in the nitration of 2-benzylpyridine.
i found something that says "The nitration occurs selectively at the benzene ring.  This is because the NH+ of protonated pyridine is much more electronegative than CH in benzene"
i'm not sure how something with a positive charge can be electronegative if its missing electrons.
maybe it means the negative charge on the O?

2) explain why nitration of the pyridine ring does not ocur.
 i read on a thread on here that if the rxn is carried out under 10degrees c then nitration is favoured. but we did our between 0-5degrees c and obviously this is not the case.

the added sulphuric acid and red fuming nitric acid to the benzylpyridine.

[rucik5]

Hi.
Pyridine ring is electron poor (when compared to benzene) due to presence of the nitrogen, which pulls electrons towards itself via the inductive effect, and thus it doesn't undergo electrophilic substitution easily. You really need to push unsubstituted pyridine to nitrate it. The nitration in strong acid presumably goes via the pyridinium ion, which is even less reactive.

"The nitration occurs selectively at the benzene ring.  This is because the NH+ of protonated pyridine is much more electronegative than CH in benzene"

I must say i don't know what that means.
Regioselectivity for the two nitro groups is explained by the electron-donating effect of the CH2-, which is also ortho-/para- directing. The first nitro group should land ortho-, and the second nitration should be slower, since now you've got an electron withdrawing group, which is deactivating the ring.
Anyone is welcome to extrapolate or correct what I said