Which of the following molecules have four degrees of unsaturation? Select all that are correct. Which of the following molecules, all of which have a molecular weight of 128 , is consistent with the mass spectrum shown below? None What factors influence 1H NMR chemical shifts? Select all that apply. The presence of electronegative atoms. Resonance involving electron-donating and electronwithdrawing groups. p-electron ring currents. The degree of substitution. The presence of 13C