Although benzene itself absorbs at 128 ppm in its 13C NMR spectrum, the carbons of substit...

Although benzene itself absorbs at 128 ppm in its 13C NMR spectrum, the carbons of substituted benzenes absorb either upfield or downfield from this value depending on the substituent. Explain the observed values for the carbon ortho to the given substituent in the monosubstituted benzene derivatives X and Y.