Propose a structure for C4H9N, which does not liberate a gas when treated with NaNO2 and HCL, and has IR absorptions at 917, 990, and 1640, as well as an N-H absorption at 3300. The 13C NMR spectrum is as follows: 36, 54.4, 115.8, 136.7. Please explain we have not covered this topic.