Which one of the following molecular vibrations is infrared-inactive? 

(a) The C = O symmetrical stretch of CO₂;

(b) The C = O unsymmetrical stretch of CO₂. (See Fig. 12.8)

Transcribed Image Text:

FIGURE 12.8 Normal vibra- tional modes of a typical CH₂ group in a structure R-CH₂-R. In each model, the white spheres are the hydrogens, the black sphere is the carbon of the CH₂, and the blue spheres represent the R groups. The center model in each normal mode represents the average position of the hydrogens. For each mode, start at the center and view left, center, right, center to see how the hydrogens move with time. average position time symmetrical stretch unsymmetrical stretch unsymmetrical in-plane bend (rock) symmetrical in-plane bend (scissor) symmetrical out-of-plane bend (wag) unsymmetrical out-of-plane bend (twist)