A student is studying four C₄ hydrocarbons shown below, each drawn as a condensed structural formula at the level of connectivity only (no stereochemical information is provided).
I. CH₃CH₂CH=CH₂ (1-butene)
II. CH₃CH=CHCH₃ (2-butene)
III. (CH₃)₂C=CH₂ (2-methylprop-1-ene)
IV. CH₂=C=CHCH₃ (1,2-butadiene)
For each compound, the student wants to know whether at least two distinct geometric isomers (cis/trans or E/Z) are possible.
(a) For each of the four compounds, state whether geometric isomerism is possible. Organize your answer in a clearly labeled table.
(b) For every compound you identified as capable of geometric isomerism, draw the complete set of geometric isomers, using conventional E/Z or cis/trans notation as appropriate.
(c) Provide a brief justification for one compound that can form geometric isomers and one compound that cannot, explicitly relating your reasoning to the identity and arrangement of substituents about the carbon–carbon multiple bond.