Generally speaking, {HEAD ~ completely aliphatic quaternary ammonium compounds} appear to provide {TAIL ~ optimal antimicrobial activity} when the largest aliphatic group is a straight chain C16 18 group and benzyl quaternary ammonium compounds appear to provide optimal antimicrobial activity when the largest aliphatic group is a straight chain C14 group 
Generally speaking , { HEAD ~ completely aliphatic quaternary ammonium compounds } appear to provide { TAIL ~ optimal antimicrobial activity } when the largest aliphatic group is a straight chain C16 18 group and benzyl quaternary ammonium compounds appear to provide optimal antimicrobial activity when the largest aliphatic group is a straight chain C14 group
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH