(a) The IR spectrum of gaseous N2O shows three strong absorption bands at 2224 cm-1, 1285 cm-1, and 2089 cm-1. In addition two quite weak bands are observed at 2563 cm-1 and 2798 cm-1 It is known that N2O is a linear molecule, but assume it is not known whether the structure is N-N-O or N-O-N. Use the IR data to decide between the two structures. What vibrations can be assigned to the strong absorption bands? What are possible causes of the weak absorptions?
(b) The IR spectrum of HCN shows three strong absorption bands at 3312 cm-1, 2089 cm-1, and 712 cm-1 From this information alone, can you deduce whether HCN is linear or nonlinear? Assuming that HCN is linear, assign vibrations to the three absorption bands.
(c) How many fundamental vibrational modes are expected for BF3? Which of these are expected to be IR active? Why? Sketch the vibrations.
(d) How many fundamental vibrational modes would you predict for (1) methane, (2) benzene, (3) toluene, (4) ethylene, and (5) carbon tetrachloride?