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Stereochemistry: importance: biochemicals medicine

Section 21-4 Hydrocarbon Isomers Distinguish between the two main categories of isomers—structural isomers and stereoisomers. Differentiate between geometric isomers with cis- and transprefixes. Describe the structural variation in molecules that results in optical isomers.

Section 21-4 Section 21.4 Hydrocarbon Isomers (cont.) isomer structural isomer stereoisomer geometric isomer Some hydrocarbons have the same molecular formula but have different molecular structures. chirality asymmetric carbon optical isomer optical rotation

Section 21-4 Structural Isomers Isomers are two or more compounds that have the same molecular formula but different molecular structures.Isomers Structural isomers have the same chemical formula but their atoms are bonded in different arrangements.Structural isomers

Section 21-4 Structural Isomers (cont.) There are two main classes of isomers: structural isomers and stereoisomers. Structural isomers have different physical and chemical properties. The structure of a substance determines properties.

Isomers – different compounds with the same molecular formula. Structural Isomers – isomers that differ in which atoms are bonded to which atoms. CH 3 eg. C 4 H 10 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 n-butane isobutane

Stereoisomers – isomers that differ in the way the atoms are oriented in space, but not in which atoms are bonded to which atoms. eg. cis-2-butene trans-2-butene

optical activity – when a substance rotates the plane of plane polarized light. plane polarized light – light that has been passed through a nicol prism or other polarizing medium so that all of the vibrations are in the same plane. non-polarizedpolarized

Section 21-4 Stereoisomers Stereoisomers are isomers in which all atoms are bonded in the same order but are arranged differently in space.Stereoisomers

Section 21-4 Stereoisomers (cont.) Geometric isomers result from different arrangements of groups around a double bond.Geometric isomers Cis means on the same side, and trans means across from. Geometric isomers have different physical and chemical properties.

Stereoisomers – isomers that differ in the way the atoms are oriented in space, but not in which atoms are bonded to which atoms. eg. cis-2-butene trans-2-butene

Section 21-4 Stereoisomers (cont.)

Section 21-4 Chirality Louis Pasteur discovered two forms of crystallized tartaric acid. The forms were mirror images of each other called right and left-handed forms. The property in which a molecule exists in right and left-handed forms is called chirality. chirality

Section 21-4 Optical Isomers Chirality occurs whenever a compound contains an asymmetric carbon. Asymmetric carbon is a carbon atom that has four different atoms or groups attached to it.Asymmetric carbon The four groups can be arranged in two different ways.

Section 21-4 Optical Isomers (cont.) Isomers that result from different arrangements of four different groups around a carbon atom represent the other class of stereoisomers, called optical isomers.optical isomers Optical isomers have the same physical and chemical properties except in chemical reactions where chirality is important.

Section 21-4 Optical Isomers (cont.) When polarized light passes through a solution containing an optical isomer, the plane of polarization is rotated to the right by the D-isomer and to the left by the L- isomer, producing and effect called optical rotation.optical rotation

A.A B.B C.C D.D Section 21-4 Assessment What are two molecules with the same formula but different structures called? A.isotopes B.chiral C.isomers D.asymmetric

A.A B.B C.C D.D Section 21-4 Assessment Which type of substances have the same physical and chemical properties but produce different optical rotations? A.isomers B.geometric isomers C.isotopes D.optical isomers

Study Guide 4 Hydrocarbon Isomers Key Concepts Isomers are two or more compounds with the same molecular formula but different molecular structures. Structural isomers differ in the order in which atoms are bonded to each other. Stereoisomers have all atoms bonded in the same order but arranged differently in space.

A.A B.B C.C D.D Chapter Assessment 4 A carbon bonded to four different groups is ____. A.cyclic B.aromatic C.asymmetric D.left-handed

A.A B.B C.C D.D STP 1 Molecules that have the same formula and the atoms are bonded in the same order but are arranged differently in space, and have different properties are ____. A.structural isomers B.geometric isomers C.optical isomer D.sterioisotopes

Definitions Stereoisomers – compounds with the same connectivity, different arrangement in space Enantiomers – stereoisomers that are non- superimposible mirror images; only properties that differ are direction (+ or -) of optical rotation Diastereomers – stereoisomers that are not mirror images; different compounds with different physical properties

Summary—Types of isomers