Chapter 12 Organic Compounds with Oxygen and Sulfur 12.6 Chiral Molecules

Isomers Molecules are structural isomers when they have the same molecular formula, but different bonding arrangements.

Stereoisomers Stereoisomers have identical molecular formulas, but they are not structural isomers. In stereoisomers, the atoms are bonded in the same sequence but differ in the way they are arranged in space. When stereoisomers have mirror images that are different, they are said to have “handedness.”

Chiral Molecules Have Handedness have the same number of atoms arranged differently in space have one or more chiral carbon atoms, each of which is bonded to four different groups are like your hands Try to superimpose your thumbs, palms, back of hands, and little fingers.

Some Everyday Chiral and Achiral Objects

Chiral Carbon Atoms Are Mirror Images The mirror images of chiral compounds cannot be superimposed. When the H and I atoms are aligned, the Cl and Br atoms are on opposite sides.

Achiral Structures Are Superimposable When the mirror image of an achiral structure is rotated, the structure can be aligned with the initial structure. Thus this mirror image is superimposable.

Learning Check A. C H l B. C. B r Identify each as a chiral or an achiral compound. A. C H 2 3 l B. C. B r

Solution chiral achiral chiral A. C H l B. C. B r Identify each as a chiral or an achiral compound. chiral achiral chiral A. C H 2 3 l B. C. B r

Fischer Projections A Fischer projection is a two-dimensional representation of a three-dimensional molecule places the most oxidized group at the top uses vertical lines in place of dashes for bonds that go back uses horizontal lines in place of wedges for bonds that come forward

Drawing Fischer Projections

D and L Notations By convention, the letter L is assigned to the structure with the –OH on the left. The letter D is assigned to the structure with the –OH on the right.

Learning Check Indicate whether each pair is a mirror image that cannot be superimposed (enantiomers).

Solution Indicate whether each pair is a mirror image that cannot be superimposed (enantiomers). Yes No

Concept Map – Organic Molecules with O and S