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Questions and Answers
What is a molecule that is superimposable on its mirror image called?
What is a molecule that is superimposable on its mirror image called?
- Enantiomer
- Chiral
- Achiral (correct)
- Stereoisomer
What is the term for isomers that differ only in the three-dimensional arrangement of substituents?
What is the term for isomers that differ only in the three-dimensional arrangement of substituents?
- Stereoisomers (correct)
- Chiral molecules
- Enantiomers
- Tetrahedral stereogenic centers
What is a carbon atom bonded to four different groups called?
What is a carbon atom bonded to four different groups called?
- Chiral molecule
- Tetrahedral stereogenic center (correct)
- Stereoisomer
- Enantiomer
What is the result of interchanging two groups on a tetrahedral stereogenic center?
What is the result of interchanging two groups on a tetrahedral stereogenic center?
What is a characteristic of achiral molecules?
What is a characteristic of achiral molecules?
What is the definition of a chiral molecule?
What is the definition of a chiral molecule?
What is the term for a mirror image that is not superimposable?
What is the term for a mirror image that is not superimposable?
What is the primary focus of stereochemistry in organic chemistry?
What is the primary focus of stereochemistry in organic chemistry?
What is the main difference between constitutional isomers and stereoisomers?
What is the main difference between constitutional isomers and stereoisomers?
What do stereoisomers have in common?
What do stereoisomers have in common?
Which of the following is a characteristic of chiral molecules?
Which of the following is a characteristic of chiral molecules?
What is the difference between a chiral molecule and its mirror image?
What is the difference between a chiral molecule and its mirror image?
What is the characteristic of achiral molecules?
What is the characteristic of achiral molecules?
Why do stereoisomers have the same physical properties?
Why do stereoisomers have the same physical properties?
What is the characteristic of a carbon atom that is a tetrahedral stereogenic center?
What is the characteristic of a carbon atom that is a tetrahedral stereogenic center?
Which of the following molecules has a plane of symmetry?
Which of the following molecules has a plane of symmetry?
What should you omit from consideration when looking for stereogenic centers?
What should you omit from consideration when looking for stereogenic centers?
How many stereogenic centers does 2-butanol have?
How many stereogenic centers does 2-butanol have?
What is the characteristic of a molecule with one tetrahedral stereogenic center?
What is the characteristic of a molecule with one tetrahedral stereogenic center?
Why is C3 a stereogenic center in 3-methylcyclohexene?
Why is C3 a stereogenic center in 3-methylcyclohexene?
What is the result of 3-methylcyclohexene having one tetrahedral stereogenic center?
What is the result of 3-methylcyclohexene having one tetrahedral stereogenic center?
What is the main component of a polarimeter that holds the substance being examined for optical activity?
What is the main component of a polarimeter that holds the substance being examined for optical activity?
What is the purpose of the two lenses in a polarimeter?
What is the purpose of the two lenses in a polarimeter?
What happens when a substance does not affect the plane of polarization?
What happens when a substance does not affect the plane of polarization?
What is the term for a substance that rotates the plane of polarization to the right?
What is the term for a substance that rotates the plane of polarization to the right?
What symbol is used to indicate a rotation to the left?
What symbol is used to indicate a rotation to the left?
What is the purpose of adjusting the lenses in a polarimeter?
What is the purpose of adjusting the lenses in a polarimeter?
What happens when a substance is optically active?
What happens when a substance is optically active?
What is the term for a substance that rotates the plane of polarization to the left?
What is the term for a substance that rotates the plane of polarization to the left?
What is the function of the light source in a polarimeter?
What is the function of the light source in a polarimeter?
A polarimeter consists of a light source, one lens, and a tube to hold the substance being examined.
A polarimeter consists of a light source, one lens, and a tube to hold the substance being examined.
The maximum amount of light reaches our eye when the two lenses are arranged to pass light vibrating in perpendicular planes.
The maximum amount of light reaches our eye when the two lenses are arranged to pass light vibrating in perpendicular planes.
A substance is said to be optically active if it does not affect the plane of polarization.
A substance is said to be optically active if it does not affect the plane of polarization.
If the rotation of the plane of polarization is to the right, the substance is levorotatory.
If the rotation of the plane of polarization is to the right, the substance is levorotatory.
The symbol (-) is used to indicate a rotation to the right.
The symbol (-) is used to indicate a rotation to the right.
A polarimeter is used to examine the optical activity of a substance.
A polarimeter is used to examine the optical activity of a substance.
A substance is optically inactive if it rotates the plane of polarization.
A substance is optically inactive if it rotates the plane of polarization.
The lenses in a polarimeter are arranged to pass light vibrating in perpendicular planes when the tube is empty.
The lenses in a polarimeter are arranged to pass light vibrating in perpendicular planes when the tube is empty.
The rotation of the plane of polarization is measured by rotating the lens nearer the eye.
The rotation of the plane of polarization is measured by rotating the lens nearer the eye.
A polarimeter is used to measure the physical properties of a substance.
A polarimeter is used to measure the physical properties of a substance.
Study Notes
Stereochemistry
- Stereochemistry is the part of organic chemistry that deals with structure in three dimensions.
- Isomers are different compounds that have the same molecular formula.
Constitutional Isomers
- Constitutional (or structural) isomers differ in the way the atoms are connected to each other.
- Constitutional isomers have:
- Different IUPAC names.
- The same or different functional groups.
- Different physical properties.
- Different chemical properties.
Stereoisomers
- Stereoisomers differ only in the way atoms are oriented in space.
- Stereoisomers have identical IUPAC names (except for a prefix like cis or trans).
- Stereoisomers always have the same functional group(s) because they differ only in the three-dimensional arrangement of atoms.
Chiral and Achiral Molecules
- A molecule (or object) that is not superimposable on its mirror image is said to be chiral.
- Chiral molecules contain one or more stereogenic centers.
- A carbon atom bonded to four different groups is a tetrahedral stereogenic center.
- A molecule that is superimposable on its mirror image is said to be achiral.
Plane of Symmetry
- A plane of symmetry is a mirror plane that cuts a molecule in half, so that one half of the molecule is a reflection of the other half.
- Achiral molecules usually contain a plane of symmetry but chiral molecules do not.
Enantiomers
- Enantiomers are mirror images that are not superimposable.
- CHBrClF is a chiral molecule, and its mirror image is a different compound.
- Enantiomers are isomers differing only in the three-dimensional arrangement of substituents.
Polarimeter
- A polarimeter is used to examine the optical activity of a substance.
- If a substance does not affect the plane of polarization, it is optically inactive.
- If a substance rotates the plane of polarization, it is optically active.
Tetrahedral Stereogenic Centers
- Any carbon atom bonded to four different groups is a tetrahedral stereogenic center.
- To locate a stereogenic center, examine each tetrahedral carbon atom in a molecule and look at the four groups (not the four atoms) bonded to it.
- Always omit from consideration all C atoms that can’t be tetrahedral stereogenic centers, including CH2 and CH3 groups, and sp or sp2 hybridized C.
Drawing a Pair of Enantiomers
- Any molecule with one tetrahedral stereogenic center is a chiral compound and exists as a pair of enantiomers.
- To draw both enantiomers, use the typical convention for depicting a tetrahedron: place two bonds in the plane, one in front of the plane on a wedge, and one behind the plane on a dash.
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Description
Test your understanding of stereochemistry, a fundamental concept in organic chemistry that deals with the three-dimensional structure of molecules. This quiz covers the types of isomers, including constitutional and stereoisomers, and their differences in molecular formula and physical properties.
