Vinyl and Formyl Hydrogen Chemical Shifts

Two carbons connected by a double (i.e., a + 71) bond are called vinyl or olefinic carbons. Each vinyl carbon is nominally sp hybridized and attached to three atoms (one of which is the other vinyl carbon). These three atoms describe an approximately equilateral triangle, which is why vinyl carbons are also described as trigonal. Hydrogens attached directly to vinyl carbons are called vinyl (or olefinic) hydrogens. 

Vinyl hydrogens typically appear in the 8 4.5-7.0 region of the H spectrum. We can establish a list of substituent parameters for vinyl substituents (Table 6.4) similar to the one we had for methyl substituents (Table 6.2). Notice that the magnitude of a substituent s (de)shielding effect is strongly 

TABLE 6.4 Substituent Parameters (A5x, ppm) for Vinyl Hydrogen Chemical Shifts  

---