Electronegative groups are "deshielding" and tend to move NMR signals from attached carbons further "downfield" (to higher ppm values).
The -system of alkenes, aromatic compounds and carbonyls strongly deshield C nuclei and move them "downfield" to higher ppm values.
Carbonyl carbons are strongly deshielded and occur at very high ppm values. Within this group, carboxylic acids and esters tend to have the smaller values, while ketones and aldehydes have values 200.
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C NMR Chemical Shifts for
-system of alkenes, aromatic compounds and carbonyls strongly deshield 
values, while ketones and aldehydes have values 
200.