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How does the connectivity of atoms change between constitutional isomers?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

Constitutional isomers, also known as structural isomers, are chemical compounds that share the same molecular formula—meaning they contain the same number and types of atoms—but differ in how those atoms are connected to one another.12

While the individual components remain the same, the specific order or arrangement of the bonds between them changes. For example, in the case of butane and isobutane, both possess the formula $C_{4} H_{10}$ , but their connectivity differs: butane features a continuous chain of four carbon atoms, whereas isobutane exhibits a branched structure.12

Because these differences in connectivity result in distinct spatial arrangements of atoms, constitutional isomers function as unique molecules with their own specific chemical and physical properties. This is distinct from stereoisomers, where the connectivity remains identical but the orientation of the parts in space differs.12