Carbon-Carbon Bond Stretching Stronger bonds absorb at higher frequencies: >C-C 1200cm-1 >C=C 1660cm-1 >C=C <2200 cm-1 (weak or absent if internal) Conjugation lowers the frequency: >isolated C=C 1640-1680cm-1 >conjugated C=C 1620-1640cm-1 >aromatic C=C approx.1600 cm-1 Chapter 12 16
Chapter 12 16 Carbon-Carbon Bond Stretching • Stronger bonds absorb at higher frequencies: ➢C-C 1200 cm-1 ➢C=C 1660 cm-1 ➢CC <2200 cm-1 (weak or absent if internal) • Conjugation lowers the frequency: ➢isolated C=C 1640-1680 cm-1 ➢conjugated C=C 1620-1640 cm-1 ➢aromatic C=C approx. 1600 cm-1 =>
Carbon-Hydrogen Stretching Bonds with more s character absorb at a higher frequency. >sp3 C-H,just below 3000 cm-1 (to the right) >sp2 C-H,just above 3000 cm-1 (to the left) >sp C-H,at 3300 cm-1 => Chapter 12 17
Chapter 12 17 Carbon-Hydrogen Stretching Bonds with more s character absorb at a higher frequency. ➢sp3 C-H, just below 3000 cm-1 (to the right) ➢sp2 C-H, just above 3000 cm-1 (to the left) ➢sp C-H, at 3300 cm-1 =>