Carbon compound protonation electronegativity

Substituent effects (substituent increments) tabulated in more detail in the literature demonstrate that C chemical shifts of individual carbon nuclei in alkenes and aromatic as well as heteroaromatic compounds can be predicted approximately by means of mesomeric effects (resonance effects). Thus, an electron donor substituent D [D = OC//j, SC//j, N(C//j)2] attached to a C=C double bond shields the (l-C atom and the -proton (+M effect, smaller shift), whereas the a-position is deshielded (larger shift) as a result of substituent electronegativity (-/ effect). 

In organic compounds having C—H bonds, the carbon atom being more electronegative will pull the bonding electron towards itself and so hydrogen can go out as a proton. Therefore, in presence of a base this H will be attracted by the base and a carbanion will be obtained. This acidic hydrogen will be abstracted by bases like NaOH, t-BuOe or alkyl lithium where the alkyl radical will behave like a base. 

Proton chemical shifts are very valuable for the determination of structures, but to use the shifts in this way we must know something about the correlations that exist between chemical shift and structural environment of protons in organic compounds. The most important effects arise from differences in electronegativity, types of carbon bonding, hydrogen bonding, and chemical exchange. 

The next compound has only one carbonyl group but gains a little acidity from the electronegative chlorine atom - it is a proton from that side of the ketone that is lost. Delocalizing the charge on to the carbon atoms shows this. 

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