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Isomers quiz #1

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  • Which of the following pairs of formulas represent isomers: pairs of compounds that have the same molecular formula but differ in connectivity or spatial orientation?
    Isomers are compounds with the same molecular formula but different connectivity (structural isomers) or spatial arrangement (stereoisomers). To determine if a pair represents isomers, check if both have identical molecular formulas but differ in either how atoms are connected or arranged in space. For example, C4H10 as n-butane (straight chain) and isobutane (branched chain) are structural isomers, while cis-2-butene and trans-2-butene (both C4H8) are geometric (stereoisomers).
  • What distinguishes a structural (constitutional) isomer from a stereoisomer?
    Structural isomers differ in the connectivity of their atoms, while stereoisomers have the same connectivity but differ in the spatial arrangement of their atoms.
  • How can you quickly identify if two molecules are optical isomers?
    You can imagine placing a mirror between the two molecules; if one is the non-superimposable mirror image of the other, they are optical isomers.
  • What is the key feature that allows geometric isomers to exist?
    Geometric isomers exist due to restricted rotation around a double bond, leading to different spatial arrangements of substituent groups.
  • How do you differentiate between cis and trans geometric isomers?
    Cis isomers have substituent groups on the same side of the double bond, while trans isomers have them on opposite sides.
  • What is a simple method to draw the optical isomer of a molecule with wedged and dashed bonds?
    Invert the solid wedged bonds to dashed and dashed bonds to solid, keeping all other atoms in the same position.
  • Why can't optical isomers be superimposed on each other?
    Optical isomers are non-superimposable mirror images, meaning their three-dimensional arrangements cannot be perfectly overlaid.
  • What molecular formula do both n-butane and isobutane share?
    Both n-butane and isobutane share the molecular formula C4H10.
  • What type of isomerism is present when two molecules have the same molecular formula and connectivity but differ in the arrangement of atoms in space?
    This is stereoisomerism.
  • What visual clue in a molecular structure often indicates the presence of geometric isomerism?
    The presence of a double bond with different groups attached to each carbon is a visual clue for geometric isomerism.