Example 7.3: Electronegativity and Bond Polarity
Bond polarities play an important role in determining the structure of proteins. Using the electronegativity values in
Figure 6, arrange the following covalent bonds — all commonly found in amino acids — in order of increasing polarity. Then designate the positive and negative atoms using the symbols δ+ and δ–:
C–H, C–N, C–O, N–H, O–H, S–H
Solution
The polarity of these bonds increases as the absolute value of the electronegativity difference increases. The atom with the δ– designation is the more electronegative of the two.
Table 1 shows these bonds in order of increasing polarity.
\(\mathrm{ΔEN}_{\mathrm{\ce{C-H}}}\) \(= 0.4\)
\(\mathrm{ΔEN}_{\mathrm{\ce{S–H}}}\) \(= 0.4\)
\(\mathrm{ΔEN}_{\mathrm{\ce{C–N}}}\) \(= 0.5\)
\(\mathrm{ΔEN}_{\mathrm{\ce{N–H}}}\) \(= 0.9\)
\(\mathrm{ΔEN}_{\mathrm{\ce{C–O}}}\) \(= 1.0\)
\(\mathrm{ΔEN}_{\mathrm{\ce{O–H}}}\) \(= 1.4\)