[Bertran05]

Hi People,

1. I have a proton spectra of a molecule. This molecules has a methylene binding to oxygen (CH2-O) and other    methylene to nitrogen (CH2-N). I know that chemichal shift is difference because Oxygen is more electronegative than Nitrogen and then the chemichal shift for CH2-O is deshielded (4.5 ppm) and for CH2-N is 3.6 ppm. But I have no idea about why happens...I mean...is a question of electron density? or what?

2. And if you have a quaternary Nitrogen like CH2-N+ (with a positive charge) then the chemical shift of protons are more deshielded than protons of methylene when u have tertiary nitrogen (CH2-N). Why? its a question of loss electron density?

Thanks for u *delete me*!!

Ciao!

[macman104]

When something is "deshielded", you are talking about the relative electron density that can shield that nucleus from the magnet.  So, if oxygen is more electronegative than nitrogen, how might that influence the available density near the hydrogens on the methylene?

Likewise, now instead of a neutral molecule, such as CH₂-O or CH₂-N, both of which have lone pairs on the heteroatom, you now have a positive charge on the nitrogen, does this have more or less available electron density than the neutral molecules?