Chemistry · Ch 14 — Basic Principles of Organic Chemistry
Isomerism
Isomerism
Isomerism is the phenomenon in which two or more genuinely DIFFERENT compounds nonetheless share exactly the same molecular formula; any two (or more) such compounds are called isomers of one another. Two fundamentally different flavours of isomerism are observed among organic compounds. STRUCTURAL isomerism occurs when two or more compounds share the same molecular formula but have a DIFFERENT structural formula -- meaning the actual pattern of which atom is bonded to which is genuinely different between them, even though the raw count of each type of atom is identical. STEREOISOMERISM, by contrast, occurs when two or more compounds instead share BOTH the same molecular formula AND the same structural formula, but differ only in the relative SPATIAL (three-dimensional) arrangement of their groups or atoms -- so on paper (in a flat 2-D structural formula) they would look identical, and only a genuinely 3-D representation reveals the difference between them. This chapter develops only structural isomerism in real detail (in section 14.5.1 immediately following); stereoisomerism is lef …
Worked out. An activity box asks students to observe two given structural formulae (an ester-type structure, CH3-CO-O-C2H5, and an aldehyde-type structure, CH3-CH2-CO-H, as best read from the source), find their molecular formulae, note the difference between them, and state the relationship between the two compounds -- functioning as a hands-on lead-in that primes the definition of structural isomerism given immediately afterward in 14.5. …