Textbook Question
In Problem 5-3, you drew the enantiomers for a number of chiral compounds. Now go back and designate each asymmetric carbon atom as either (R) or (S).
(a)
(b)
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Ch.5 - Stereochemistry
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 5, Problem 8a
A solution of 2.0 g of (+)-glyceraldehyde, HOCH2CHOHCHO, in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of +1.74° was found at 25 °C. Determine the specific rotation of (+)-glyceraldehyde
Verified step by step guidance1
Step 1: Recall the formula for specific rotation: \( [\alpha] = \frac{\alpha}{l \cdot c} \), where \( [\alpha] \) is the specific rotation, \( \alpha \) is the observed rotation, \( l \) is the path length in decimeters, and \( c \) is the concentration in g/mL.
Step 2: Convert the path length from millimeters to decimeters. Since the cell length is 100 mm, divide by 1000 to convert to meters, then multiply by 10 to convert to decimeters. This gives \( l = 0.1 \, \text{dm} \).
Step 3: Calculate the concentration \( c \) of the solution. Divide the mass of glyceraldehyde (2.0 g) by the volume of water (10.0 mL). This gives \( c = \frac{2.0}{10.0} \, \text{g/mL} \).
Step 4: Substitute the observed rotation \( \alpha = +1.74° \), the path length \( l = 0.1 \, \text{dm} \), and the concentration \( c = 0.2 \, \text{g/mL} \) into the formula \( [\alpha] = \frac{\alpha}{l \cdot c} \).
Step 5: Simplify the expression to find the specific rotation \( [\alpha] \). Ensure units are consistent and the calculation is performed correctly.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Specific Rotation
Specific rotation is a property of chiral compounds that quantifies their ability to rotate plane-polarized light. It is defined as the observed rotation of light in degrees divided by the path length in decimeters and the concentration in grams per milliliter. The formula is [α] = α / (l × c), where [α] is the specific rotation, α is the observed rotation, l is the path length, and c is the concentration.
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Specific rotation vs. observed rotation.
Chirality
Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image, much like left and right hands. Chiral molecules often exist as enantiomers, which are pairs of molecules that are mirror images of each other. The presence of chiral centers, typically carbon atoms bonded to four different substituents, is a key factor in determining a molecule's optical activity.
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Optical Activity
Optical activity is the ability of chiral substances to rotate the plane of polarized light. This phenomenon occurs due to the asymmetric arrangement of atoms in chiral molecules. The direction and degree of rotation depend on the specific compound, its concentration, and the wavelength of light used. Measuring optical activity is crucial in determining the purity and concentration of chiral compounds in solution.
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Related Practice
Textbook Question
Write structural formulas for the following compounds (includes both old- and new-style names).(j) vinylacetylene(k) (S)-3-methyl-1-penten-4-yne
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Textbook Question
A chiral sample gives a rotation that is close to 180°. How can one tell whether this rotation is +180° or -180°?
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Textbook Question
In Problem 5-3, you drew the enantiomers for a number of chiral compounds. Now go back and designate each asymmetric carbon atom as either (R) or (S).
(c)
(d) 1-bromo-2-methylbutane
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Textbook Question
In Problem 5-3, you drew the enantiomers for a number of chiral compounds. Now go back and designate each asymmetric carbon atom as either (R) or (S).
(e) chlorocyclohexane
(f) cis-1,2-dichlorocyclobutane
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Textbook Question
A solution of 0.50 g of (−)-epinephrine (see Figure 5-16) dissolved in 10.0 mL of dilute aqueous HCl was placed in a 20-cm polarimeter tube. Using the sodium D line, the rotation was found to be −5.1° at 25 °C. Determine the specific rotation of epinephrine.
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