Hybridisation electronegativity, effect

Any effect which alters the density or spatial distribution of electrons around a nucleus will alter the degree of shielding and hence its chemical shift. H chemical shifts are sensitive to both the hybridisation of the atom to which the H nucleus is attached sp, sp etc.) and to electronic effects (the presence of neighbouring electronegative/electropositive groups). 

The sensitivity of 2J(POP) to changes in the hybridisation and electronegativity has been demonstrated for ATP. This effect is also noticeable when comparing ligands and related adducts, for example (1968>34)... 

The 13C spectrum of crotonaldehyde (CH3 CH=CH CHO Fig. 3.52) provides a good example of the way in which the 13C chemical shift is determined both by the state of hybridisation of the carbon atom and the nature of the substituent. The four carbon atoms have markedly different chemical shifts. The methyl carbon appears at 3 17.1. It is shifted downfield slightly compared to the methyl carbon at the end of a chain of methylene groups as in 3-methylheptane (Fig. 3.41) and hex-l-ene (Fig. 3.51). The two alkenyl carbons appear at <5133.4 and 3 152.9. The effect of conjugation of the carbon-carbon double bond is that the (i-carbon is shifted further downfield. The carbon of the carbonyl group is sp2-hybridised and is directly bonded to an electronegative atom. It is shifted furthest downfield and appears at 3 192.2,... 

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