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15.4 Physical Properties

15.5 Chiral Molecules

Chapter 15 Aldehydes, Ketones, and Chiral Molecules

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Physical Properties The polar carbonyl group provides

dipole-dipole interactions. + - + -

C=O 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.

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Comparison of Boiling Points

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

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Solubility in Water

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

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Comparison of Physical Properties

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Types of Isomers

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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.

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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.

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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.

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Some Everyday Chiral and Achiral Objects

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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.

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Drawing Fischer Projections

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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.