\footnotesize
\schemestart
\chemfig{H-C(-[2]H)(-[6]H)-C(-[2]H)(-[6]H)-O(-[7]H)} \+
\chemfig{O_2} \arrow
\chemfig{H-C(-[2]H)(-[6]H)-C(=[1]O)-[7]O-H} \+
\chemfig{H_2O}
\schemestop