Science, Tech, Math › Science Ipso, Meso, and Peri Substitutions in Organic Chemistry Ring Substitutions of Organic Molecules Share Flipboard Email Print This shows the difference between ipso-, meso- and peri- arene substitution patterns. Todd Helmenstine Science Chemistry Molecules Basics Chemical Laws Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated August 06, 2018 The prefixes ipso-, meso-, and peri- describe ring substitutions in organic chemistry. They are part of the IUPAC nomenclature used to specify the position of any non-hydrogen substituents in an aromatic hydrocarbon. Ipso Substitution The ipso- prefix is used when two substituents share the same ring position in an intermediate compound. This could occur in an electrophilic aromatic ring substitution. Meso Substitution The meso- prefix is used when substituents occupy a benzylic position when the first carbon covalently bonds adjacent to a benzene or other aromatic ring. It is seen in acridines and calixarenes. Peri Substitution The peri- prefix is used to describe substituents at the 1 and 8 positions. It is seen specifically in naphthalenes. In addition to ipso, meta, and peri, there are two other ring substitution patterns you may encounter. There is the ortho, meta, and para substitution and the cine and tele substitution. Cine and Tele Substitution In the cine- substitution, the entering group is positioned adjacent to the one that was occupied by the leaving group. This is seen in aryne chemistry. In the tele- substitution, the new position of the entering group is more than one atom further away on the aromatic ring.