CH2−C\mathrm{CH}_{2}-\mathrm{C}CH2−C
C2H5Cl\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}C2H5Cl
HCl\mathrm{HCl}HCl
POCl3\mathrm{POCl}_{3}POCl3
C&D \text { C\&D } C&D