8  4        CHCHOH                        OH          CHCH－                      －OH                      －OH                                   CHOH＋HI→CHI＋HO
 
CHCHCHCHOH＋HI→CHCHCHCHI＋HO
                                     
CHCHCHCHCHCHCHCHOH＋HI→CHCHCHCHCHCHCHCHI＋HO
                                                                                                                                                                             
       －OH   I      
                                                    8—2                           —        
 8—2      