Stretching Frequencies TABLE 12-1 Bond Stretching Frequencies In a group of bonds with similar bond energies,the frequency decreases with increasing atomic weight.In a group of bonds between similar atoms,the frequency increases with bond energy. The bond energies and frequencies listed hereare approximate. Bond Bond Energy [kJ(kcal)] Stretching Frequency(cm) Frequency decreases with increasing atomic mass C一H 420(100) 3000 C-D heavier atoms 420(100) 2100 y decreases C-C 350(83) 1200 Frequency increases with bond energy C-C 350(83) 1200 C=C 611(146) stronger 1660 v increases C=C bond 840(200) 2200 C-N 305(73) 1200 C=N 615(147) 1650 C=N 891(213) 2200 C-0 360(86) 1100 C=0 745(178) 1700 Copyright2010 Pearson Prentice Hall.Inc. Frequency decreases with increasing atomic mass. Frequency increases with increasing bond energy. Chapter 12 9 Chapter 12 9 Stretching Frequencies • Frequency decreases with increasing atomic mass. • Frequency increases with increasing bond energy