Ch. 7 - Structure and Synthesis of Alkenes; Elimination

Wade9th EditionOrganic ChemistryISBN: 9780135213728당신이 사용하는 게 아니라요?교과서 변경

Wade 9th Edition

Ch. 7 - Structure and Synthesis of Alkenes; Elimination

문제 9a

7장, 문제 9a

How many stereogenic double bonds are in octa-1,3,5-triene? How many stereocenters are there? Draw and name the four stereoisomers of octa-1,3,5-triene.

검증된 단계별 안내

Step 1: Identify the structure of octa-1,3,5-triene. This compound is an eight-carbon chain with three double bonds located at positions 1, 3, and 5. Draw the structure to visualize the molecule.

Step 2: Determine the stereogenic double bonds. A stereogenic double bond is a double bond that can exhibit cis-trans (E/Z) isomerism. For this to occur, each carbon in the double bond must have two different substituents. Analyze the double bonds at positions 1, 3, and 5 to see if they meet this criterion.

Step 3: Count the stereocenters. A stereocenter is a carbon atom bonded to four different groups. Examine the structure of octa-1,3,5-triene to identify any such carbons. Note that stereogenic double bonds are not stereocenters, as they involve sp2-hybridized carbons.

Step 4: Draw the four stereoisomers of octa-1,3,5-triene. Since there are stereogenic double bonds, assign E/Z configurations to each double bond. Combine these configurations to generate all possible stereoisomers (e.g., E,E,E; E,E,Z; E,Z,Z; Z,Z,Z).

Step 5: Name each stereoisomer using the E/Z nomenclature. For each isomer, specify the configuration of the double bonds in the name (e.g., (1E,3E,5E)-octa-1,3,5-triene). Ensure the names are consistent with IUPAC rules.

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주요 개념

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Stereogenic Double Bonds

Stereogenic double bonds are carbon-carbon double bonds that can create geometric isomerism due to the restricted rotation around the double bond. In compounds with multiple double bonds, such as octa-1,3,5-triene, each double bond can potentially contribute to the overall stereochemistry of the molecule, leading to different spatial arrangements of substituents.

Stereocenters

Stereocenters are atoms in a molecule, typically carbon, that have four different substituents attached, leading to non-superimposable mirror images, or enantiomers. Identifying stereocenters is crucial for determining the number of possible stereoisomers, as each stereocenter can exist in two configurations (R or S), significantly increasing the complexity of the molecule's stereochemistry.

Stereoisomers

Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. In the case of octa-1,3,5-triene, the presence of stereogenic double bonds and stereocenters allows for the formation of multiple stereoisomers, which can be categorized into cis and trans forms, as well as different configurations at the stereocenters.

관련 실천

교과서 질문

Some of the following examples can show geometric isomerism, and some cannot. For the ones that can, draw all the geometric isomers, and assign complete names using the E-Z system.

(i)

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교과서 질문

Draw the six stereoisomers of octa-2,4,6-triene. Explain why there are only six stereoisomers, rather than the eight we might expect for a compound with three stereogenic double bonds.

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교과서 질문

Teflon-coated frying pans routinely endure temperatures that would cause polyethylene or polypropylene to oxidize and decompose. Decomposition of polyethylene is initiated by free-radical abstraction of a hydrogen atom by O₂. Bond-dissociation energies of C—H bonds are about 400 kJ/mol, and C—F bonds are about 460 kJ/mol. The BDE of the H—OO bond is about 192 kJ/mol, and the F—OO bond is about 63 kJ/mol. Show why Teflon (Figure 7-5) is much more resistant to oxidation than polyethylene is.

1208

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교과서 질문

For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?

a. cis-1,2-dichloroethene or cis-1,2-dibromoethene

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교과서 질문

Some of the following examples can show geometric isomerism, and some cannot. For the ones that can, draw all the geometric isomers, and assign complete names using the E-Z system.

e. 3-ethyl-5-methyloct-3-ene

f. 3,7-dichloroocta-2,5-diene

1164

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교과서 질문

Some of the following examples can show geometric isomerism, and some cannot. For the ones that can, draw all the geometric isomers, and assign complete names using the E-Z system.

(g)

(h)

1137

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