Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

9. Alkenes and Alkynes

Alkene Stability

Organic Chemistry

9. Alkenes and Alkynes

Alkene Stability

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5:44 minutes

Problem 86a

Textbook Question

Which species in each pair is more stable?
a.

Verified step by step guidance

Step 1: Analyze the molecular structure of each species. The first species, CH3C−HCH2CH3, contains a tertiary carbon (a carbon bonded to three other carbons) with a hydrogen attached. The second species, CH3CH2CH2C−H2, contains a primary carbon (a carbon bonded to only one other carbon) with two hydrogens attached.

Step 2: Consider the concept of carbocation stability. Tertiary carbons are generally more stable than primary carbons due to hyperconjugation and inductive effects. Hyperconjugation involves the delocalization of electrons from adjacent C-H bonds, while inductive effects involve electron donation from alkyl groups.

Step 3: Evaluate the stability of the hydrogen atoms attached to the carbon. In the first species, the hydrogen is bonded to a tertiary carbon, which is more stable due to the surrounding alkyl groups. In the second species, the hydrogens are bonded to a primary carbon, which is less stable.

Step 4: Consider steric hindrance. The first species has more steric hindrance due to the bulky groups around the tertiary carbon, but this does not significantly affect the stability of the hydrogen bond compared to the electronic effects.

Step 5: Conclude that the species with the hydrogen attached to the tertiary carbon (CH3C−HCH2CH3) is more stable than the species with hydrogens attached to the primary carbon (CH3CH2CH2C−H2), based on electronic effects such as hyperconjugation and inductive stabilization.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stability of Alkanes

The stability of alkanes is influenced by factors such as steric hindrance and hyperconjugation. Generally, branched alkanes are more stable than their straight-chain counterparts due to reduced steric strain and increased hyperconjugation, which allows for better distribution of electron density.

Hyperconjugation

Hyperconjugation is a stabilizing interaction that occurs when the electrons in a sigma bond (usually C-H or C-C) interact with an adjacent empty or partially filled p-orbital or π-bond. This interaction helps to delocalize electron density, thereby increasing the stability of the molecule.

Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups within a molecule, which can affect its stability. In alkanes, increased branching reduces steric hindrance, leading to a more stable structure compared to linear forms, where atoms are more closely packed and experience greater repulsion.

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Related Practice

Textbook Question

Explain why each of the following alkenes is stable or unstable.

(a) 1,2-dimethylcyclopentene

(b) trans-1,2-dimethylcyclopentene

(d) trans-1,2-dimethylcyclodecene

Textbook Question

A double bond in a six-membered ring is usually more stable in an endocyclic position than in an exocyclic position. Hydrogenation data on two pairs of compounds follow. One pair suggests that the energy difference between endocyclic and exocyclic double bonds is about 9 kJ/mol. The other pair suggests an energy difference of about 5 kJ/mol. Which number do you trust as being more representative of the actual energy difference? Explain your answer.

Textbook Question

Using Table 7-2 as a guide, predict which member of each pair is more stable, as well as by about how many kJ/mol or kcal/mol.

a. cis,cis-hexa-2,4-diene or trans,trans-hexa-2,4-diene

b. 2-methylbut-1-ene or 3-methylbut-1-ene

c. 2-methylbut-1-ene or 2-methylbut-2-ene

d. cis-4-methylpent-2-ene or 2-methylpent-2-ene

Textbook Question

Which species in each pair is more stable?

Textbook Question

Conjugated dienes, molecules containing two alkenes separated by one single bond, are discussed in detail in Chapter 21.

(a) Considering the observed ∆H° of hydrogenation, is hexa-1,3-diene (conjugated) or hexa-1,4-diene (unconjugated) more stable?

Textbook Question

Conjugated dienes, molecules containing two alkenes separated by one single bond, are discussed in detail in Chapter 21.

(b) How might you account for this difference in stability?

Textbook Question

Bromination of buta-1,3-diene with a single equivalent of Br₂ can give either of two products. (a) Which of these products (A or B) would you predict to be more stable? Justify your answer.

Textbook Question

Rank each group of compounds in order of increasing heat of hydrogenation.

(b)

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