In the study of chemical shifts in NMR spectroscopy, understanding the ranking of hydrogen atoms based on their deshielding effects is crucial. The most deshielded hydrogen, H5, is located on a double bond, which significantly influences its chemical environment. Following H5, H2 is next in line due to its attachment to a carbon that is bonded to fluorine, the most electronegative atom, making it an example of a ZCH (Z-configuration carbon-hydrogen bond). H3, which is associated with a triple bond, comes next, as triple bonds create a slightly lower deshielding effect compared to electronegative atoms like fluorine. H4, being an allylic hydrogen, is also classified as ZCH but is positioned lower in the ranking due to its unique structure. Finally, H1, which is simply a hydrogen on an alkane (CH), is the least deshielded.

The chemical shifts of these hydrogens are measured in parts per million (ppm) and are denoted by the Greek symbol delta (δ). For H5, the expected chemical shift ranges from 4.5 to 6 ppm, with a typical value around 5 ppm. H2, influenced by the presence of fluorine, has a shift near 4 ppm. H3, associated with a triple bond, typically shows a shift around 3 ppm. H4, being allylic, is expected to be around 1.9 ppm, slightly below 2 ppm. Lastly, H1, being secondary, has a shift closer to 1.4 ppm.

It is important to note that while these values can fluctuate, the general trends provide a solid foundation for understanding chemical shifts. Memorizing these values can be beneficial, especially for exams, as some instructors may provide different reference sheets that may not align with your understanding. Familiarity with these shifts enhances confidence and comprehension in the subject matter.