OH ROH R-O-R' R-足-Ry SH nS RSH R-S-R' R-是-HRy R-C-OH r-C-sh RNH2 R2NH RN RaNx- RPH2 R2PH RP RaPX Organic Chem Organic Chem RNH2 R2 NH R3 N R4 NX RPH2 R2 PH R3 P R4 PX ROH RSH OH SH R O R' R C H(R') O R C OH O R S R' R C H(R') S R C OH S R C SH O