[metallica00789]

Hi,
Why the carbon of esters groups has a lower C13 NMR chemical shift (170-185ppm) compared to the carbon of ketone groups (205-220 ppm). I am thinking that since the carbon of esters are next two electronegative atoms (oxygen), it should more deshielded, and thus having a higher chemical shift.
Thank you

[salteen]

You are correct in that a more electron-deficient atom will have a higher chemical shift. Try drawing the resonance structures for a ketone vs an ester, and compare the amount of electron density each carbonyl carbon experiences.