Suppose you have synthesized a new compound. Even if the combustion analysis agrees with the empirical formula of the compound you had intended to prepare, you might have made an isomer of the desired compound instead. Therefore, it is useful to be able to identify all possible isomers. Draw two-dimensional structural formulas for all the isomeric alkanes of formula C₅H₁₂.

PLAN Isomers cannot be changed into one another simply by rotating either the entire structure or parts of the structure on the page. One approach is to insert CH₂ groups into different parts of the formulas of the two C₄H₈ molecules given earlier (as 24 and 25), then discard formulas that repeat those already obtained. It is often easier to identify different conformations of the same isomer by building molecular models that allow rotation about single bonds.