Question

roberto examines two molecular models. he sees that the atoms are the same in each model and are attached in the same order in each model. however, he cannot make the models appear the same without breaking a double bond. what do the models represent?
two structural isomers that have the same molecular formula
two geometric isomers that have the same molecular formula
two organic compounds that have the same structural formula
two models of a single organic compound

Explanation:

1. Recall the definitions of isomers:

• Structural isomers have different connectivity of atoms. But the problem states atoms are attached in the same order, so structural isomers (first option) are out.
• Geometric isomers (cis - trans isomers) occur when there is a double bond (which restricts rotation) and the atoms/groups are arranged differently around the double bond, with the same molecular formula and same atom connectivity (order of attachment).
• The third option says same structural formula, but if they can't be made to look the same without breaking a double bond, they can't have the same structural formula.
• The fourth option is wrong because they can't be the same compound if they can't be made to appear the same without breaking a double bond.

1. So the key here is the presence of a double bond restricting rotation, leading to geometric isomers with the same molecular formula.

Answer:

B. two geometric isomers that have the same molecular formula