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MCAT Organic Chemistry – Molecules

  • by Kerry Goldstein
  • Feb 02, 2015
  • MCAT Blog, MCAT Organic, MCAT Question of the Day

moleculess

 

The two molecules above can best be described as:

A) Structural isomers

B) Diastereomers

C) Enantiomers

D) Conformational isomers

 

Explanation

A) Structural isomers

B) Diastereomers

C) Enantiomers

D) Conformational isomers

 

The molecule on the left is trans 1, 2-diiodocyclohexane. The molecule on the right is cis 1, 2-diiodocyclohexane. Cis and trans molecules are a type of diastereomer called geometric isomers.

A: Structural isomers have fundamentally different connectivity between the atoms. So for example if the iodine were on carbons 1 and 3 and then in the other molecule on carbons 1 and 4, that would be structural isomers.

C: Enantiomers are mirror image reflections of each other, which these molecules are not.

D: Conformations isomers allow you to freely interconvert between the molecules without breaking any bonds. The classic example is chair and boat cyclohexane. Here, to flip the one iodine from R to S configuration would require breaking a bond in the ring, rotating, and then re-attaching. That requirement for bond-breaking means these are not conformers.

 

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