Physical Properties 15.5 Chiral Molecules Chapter 15 Aldehydes, Ketones, and Chiral Molecules

2 Physical Properties The polar carbonyl group provides dipole-dipole interactions.  +  -  +  - C=O Without an H on the oxygen atom, aldehydes and ketones cannot form hydrogen bond. Aldehydes and ketones can form hydrogen bonds with the water molecules.

3 Comparison of Boiling Points Aldehydes and ketones have higher boiling points than alkanes and ethers of similar mass, but lower boiling points than alcohols.

4 Solubility in Water The electronegative O atom of the carbonyl group of aldehydes and ketones forms hydrogen bonds with water.

5 Comparison of Physical Properties

6 Types of Isomers

7 Chiral Objects Chiral compounds have the same number of atoms arranged differently in space. A chiral carbon atom is bonded to four different groups. Your hands are chiral. Try to superimpose your thumbs, palms, back of hands, and little fingers.

8 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.

9 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.

10 Some Everyday Chiral and Achiral Objects

11 Fischer Projections A Fischer projection: Is a 2-dimensional representation of a 3- 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.

12 Drawing Fischer Projections

13 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.