So it turns out that alkenes are stabilized by a force called hyperconjugation. Okay? So let's go ahead and write this down, hyperconjugation. And as you guys have already learned or will learn, hyperconjugation is a force that also stabilizes carbocations. So in fact, when we talk about alkenes, many times we'll talk about carbocations hand in hand because it's the same exact force that's stabilizing both of them. So how does this work? Basically, what it means is that in a double bond, I have a pi bond that's being formed by 2 overlapping p orbitals. Okay? That pi bond can be stabilized by having sigma bonds that are close by share electrons with it. Okay? And that's exactly what happens in hyperconjugation. So as you'll notice, what I have here is a double bond overlapping on the top and the bottom, and then what I have is an adjacent sigma bond right here, between the carbon and the H. And it turns out that the more groups that I have, the more hydrogens I have overlapping their bonds with the bonds from the pi bond, the more stable that pi bond is going to be. Because these electrons are going to be able to share and basically donate a little bit of their density to the double bond. Alright? So what that means is that the more r groups that I have around my double bond, the more stable it's going to be. Alright? And that's exactly going to be the trend that we use to determine the most stable alkene. So basically, since this phenomenon of hyperconjugation is only possible with r groups, the more substituted the alkene, the more stable it is. Okay? And that leads us to the following trend. The following trend of alkene stability just has to do with how many R groups can they pile around a double bond. So as you can see, the best kind of double bond possible would be called tetra substituted. Okay? Why? Because it's just 4 groups. That means I have the maximum number of r groups right around my double bond. As I start taking R groups away and replacing them with H, that's gonna reduce the amount of hyperconjugation that can stabilize my double bond. So as you can see trisubstituted would be next, then di, then mono, and then finally the worst, so sad face over here, is unsubstituted. Because unsubstituted can't hyperconjugate at all. There's nothing that can donate electrons to that pi bond, so it's pretty much just going to be unstable. Okay? Now it turns out that for the purposes of disubstituted, there's actually a few different ways that we can order those R groups. So let's go ahead and look into that more. Basically, when you have a disubstituted double bond, you have options. It's not like you're just going to have one type of disubstituted. You could have them where both r groups are facing the same side of the double bond, that would be cis. You could also orient them so that both sides are facing opposite sides, that would be trans. And then finally, you could orient it so that both of the r groups are on the same corner of the double bond. They're actually coming off the same carbon. And this is a word called gem, which stands for the word geminal. Okay? Just so you guys know, geminal is a position word. It's actually a word that we'll use more in Orgo 1 and Orgo 2 later. But all it means is that I have two things coming off the same carbon. The way that I like to think about it is geminal is like the word Gemini and Gemini means twins. Right? So it's like you have 2 things coming off the same carbon. These r groups are like twins. They're both coming off the same carbon. Okay? So for whatever reason it is, geminal is going to be most stable, then trans is going to be more stable than then well, trans is going to be the second most stable and then cis is going to be the least stable. Now the pattern between cis and trans is really easy to understand because cis, these groups are kind of interfering with each other. They're in each other's space. Whereas trans, they're facing opposite to each other, so they're more stable, there's more room to breathe. Now, why geminal is more stable than trans? I'm not exactly sure, but it's just something that you guys can memorize and you guys can know it for your test. Alright? So here's a really easy question just following up on what we just talked about. We have 4 alkenes here. Go ahead and try to rank them in order and of stability, and then when you're done I'll go ahead and answer it.
- 1. A Review of General Chemistry5h 5m
- Summary23m
- Intro to Organic Chemistry5m
- Atomic Structure16m
- Wave Function9m
- Molecular Orbitals17m
- Sigma and Pi Bonds9m
- Octet Rule12m
- Bonding Preferences12m
- Formal Charges6m
- Skeletal Structure14m
- Lewis Structure20m
- Condensed Structural Formula15m
- Degrees of Unsaturation15m
- Constitutional Isomers14m
- Resonance Structures46m
- Hybridization23m
- Molecular Geometry16m
- Electronegativity22m
- 2. Molecular Representations1h 14m
- 3. Acids and Bases2h 46m
- 4. Alkanes and Cycloalkanes4h 19m
- IUPAC Naming29m
- Alkyl Groups13m
- Naming Cycloalkanes10m
- Naming Bicyclic Compounds10m
- Naming Alkyl Halides7m
- Naming Alkenes3m
- Naming Alcohols8m
- Naming Amines15m
- Cis vs Trans21m
- Conformational Isomers13m
- Newman Projections14m
- Drawing Newman Projections16m
- Barrier To Rotation7m
- Ring Strain8m
- Axial vs Equatorial7m
- Cis vs Trans Conformations4m
- Equatorial Preference14m
- Chair Flip9m
- Calculating Energy Difference Between Chair Conformations17m
- A-Values17m
- Decalin7m
- 5. Chirality3h 39m
- Constitutional Isomers vs. Stereoisomers9m
- Chirality12m
- Test 1:Plane of Symmetry7m
- Test 2:Stereocenter Test17m
- R and S Configuration43m
- Enantiomers vs. Diastereomers13m
- Atropisomers9m
- Meso Compound12m
- Test 3:Disubstituted Cycloalkanes13m
- What is the Relationship Between Isomers?16m
- Fischer Projection10m
- R and S of Fischer Projections7m
- Optical Activity5m
- Enantiomeric Excess20m
- Calculations with Enantiomeric Percentages11m
- Non-Carbon Chiral Centers8m
- 6. Thermodynamics and Kinetics1h 22m
- 7. Substitution Reactions1h 48m
- 8. Elimination Reactions2h 30m
- 9. Alkenes and Alkynes2h 9m
- 10. Addition Reactions3h 18m
- Addition Reaction6m
- Markovnikov5m
- Hydrohalogenation6m
- Acid-Catalyzed Hydration17m
- Oxymercuration15m
- Hydroboration26m
- Hydrogenation6m
- Halogenation6m
- Halohydrin12m
- Carbene12m
- Epoxidation8m
- Epoxide Reactions9m
- Dihydroxylation8m
- Ozonolysis7m
- Ozonolysis Full Mechanism24m
- Oxidative Cleavage3m
- Alkyne Oxidative Cleavage6m
- Alkyne Hydrohalogenation3m
- Alkyne Halogenation2m
- Alkyne Hydration6m
- Alkyne Hydroboration2m
- 11. Radical Reactions1h 58m
- 12. Alcohols, Ethers, Epoxides and Thiols2h 42m
- Alcohol Nomenclature4m
- Naming Ethers6m
- Naming Epoxides18m
- Naming Thiols11m
- Alcohol Synthesis7m
- Leaving Group Conversions - Using HX11m
- Leaving Group Conversions - SOCl2 and PBr313m
- Leaving Group Conversions - Sulfonyl Chlorides7m
- Leaving Group Conversions Summary4m
- Williamson Ether Synthesis3m
- Making Ethers - Alkoxymercuration4m
- Making Ethers - Alcohol Condensation4m
- Making Ethers - Acid-Catalyzed Alkoxylation4m
- Making Ethers - Cumulative Practice10m
- Ether Cleavage8m
- Alcohol Protecting Groups3m
- t-Butyl Ether Protecting Groups5m
- Silyl Ether Protecting Groups10m
- Sharpless Epoxidation9m
- Thiol Reactions6m
- Sulfide Oxidation4m
- 13. Alcohols and Carbonyl Compounds2h 17m
- 14. Synthetic Techniques1h 26m
- 15. Analytical Techniques:IR, NMR, Mass Spect6h 50m
- Purpose of Analytical Techniques5m
- Infrared Spectroscopy16m
- Infrared Spectroscopy Table31m
- IR Spect:Drawing Spectra40m
- IR Spect:Extra Practice26m
- NMR Spectroscopy10m
- 1H NMR:Number of Signals26m
- 1H NMR:Q-Test26m
- 1H NMR:E/Z Diastereoisomerism8m
- H NMR Table21m
- 1H NMR:Spin-Splitting (N + 1) Rule17m
- 1H NMR:Spin-Splitting Simple Tree Diagrams11m
- 1H NMR:Spin-Splitting Complex Tree Diagrams8m
- 1H NMR:Spin-Splitting Patterns8m
- NMR Integration18m
- NMR Practice14m
- Carbon NMR4m
- Structure Determination without Mass Spect47m
- Mass Spectrometry12m
- Mass Spect:Fragmentation28m
- Mass Spect:Isotopes27m
- 16. Conjugated Systems6h 13m
- Conjugation Chemistry13m
- Stability of Conjugated Intermediates4m
- Allylic Halogenation12m
- Reactions at the Allylic Position39m
- Conjugated Hydrohalogenation (1,2 vs 1,4 addition)26m
- Diels-Alder Reaction9m
- Diels-Alder Forming Bridged Products11m
- Diels-Alder Retrosynthesis8m
- Molecular Orbital Theory9m
- Drawing Atomic Orbitals6m
- Drawing Molecular Orbitals17m
- HOMO LUMO4m
- Orbital Diagram:3-atoms- Allylic Ions13m
- Orbital Diagram:4-atoms- 1,3-butadiene11m
- Orbital Diagram:5-atoms- Allylic Ions10m
- Orbital Diagram:6-atoms- 1,3,5-hexatriene13m
- Orbital Diagram:Excited States4m
- Pericyclic Reaction10m
- Thermal Cycloaddition Reactions26m
- Photochemical Cycloaddition Reactions26m
- Thermal Electrocyclic Reactions14m
- Photochemical Electrocyclic Reactions10m
- Cumulative Electrocyclic Problems25m
- Sigmatropic Rearrangement17m
- Cope Rearrangement9m
- Claisen Rearrangement15m
- 17. Ultraviolet Spectroscopy51m
- 18. Aromaticity2h 31m
- 19. Reactions of Aromatics: EAS and Beyond5h 1m
- Electrophilic Aromatic Substitution9m
- Benzene Reactions11m
- EAS:Halogenation Mechanism6m
- EAS:Nitration Mechanism9m
- EAS:Friedel-Crafts Alkylation Mechanism6m
- EAS:Friedel-Crafts Acylation Mechanism5m
- EAS:Any Carbocation Mechanism7m
- Electron Withdrawing Groups22m
- EAS:Ortho vs. Para Positions4m
- Acylation of Aniline9m
- Limitations of Friedel-Crafts Alkyation19m
- Advantages of Friedel-Crafts Acylation6m
- Blocking Groups - Sulfonic Acid12m
- EAS:Synergistic and Competitive Groups13m
- Side-Chain Halogenation6m
- Side-Chain Oxidation4m
- Reactions at Benzylic Positions31m
- Birch Reduction10m
- EAS:Sequence Groups4m
- EAS:Retrosynthesis29m
- Diazo Replacement Reactions6m
- Diazo Sequence Groups5m
- Diazo Retrosynthesis13m
- Nucleophilic Aromatic Substitution28m
- Benzyne16m
- 20. Phenols55m
- 21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
- Naming Aldehydes8m
- Naming Ketones7m
- Oxidizing and Reducing Agents9m
- Oxidation of Alcohols28m
- Ozonolysis7m
- DIBAL5m
- Alkyne Hydration9m
- Nucleophilic Addition8m
- Cyanohydrin11m
- Organometallics on Ketones19m
- Overview of Nucleophilic Addition of Solvents13m
- Hydrates6m
- Hemiacetal9m
- Acetal12m
- Acetal Protecting Group16m
- Thioacetal6m
- Imine vs Enamine15m
- Addition of Amine Derivatives5m
- Wolff Kishner Reduction7m
- Baeyer-Villiger Oxidation39m
- Acid Chloride to Ketone7m
- Nitrile to Ketone9m
- Wittig Reaction18m
- Ketone and Aldehyde Synthesis Reactions14m
- 22. Carboxylic Acid Derivatives: NAS2h 51m
- Carboxylic Acid Derivatives7m
- Naming Carboxylic Acids9m
- Diacid Nomenclature6m
- Naming Esters5m
- Naming Nitriles3m
- Acid Chloride Nomenclature5m
- Naming Anhydrides7m
- Naming Amides5m
- Nucleophilic Acyl Substitution18m
- Carboxylic Acid to Acid Chloride6m
- Fischer Esterification5m
- Acid-Catalyzed Ester Hydrolysis4m
- Saponification3m
- Transesterification5m
- Lactones, Lactams and Cyclization Reactions10m
- Carboxylation5m
- Decarboxylation Mechanism14m
- Review of Nitriles46m
- 23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
- 24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
- Tautomerization9m
- Tautomers of Dicarbonyl Compounds6m
- Enolate4m
- Acid-Catalyzed Alpha-Halogentation4m
- Base-Catalyzed Alpha-Halogentation3m
- Haloform Reaction8m
- Hell-Volhard-Zelinski Reaction3m
- Overview of Alpha-Alkylations and Acylations5m
- Enolate Alkylation and Acylation12m
- Enamine Alkylation and Acylation16m
- Beta-Dicarbonyl Synthesis Pathway7m
- Acetoacetic Ester Synthesis13m
- Malonic Ester Synthesis15m
- 25. Condensation Chemistry2h 9m
- 26. Amines1h 43m
- 27. Heterocycles2h 0m
- Nomenclature of Heterocycles15m
- Acid-Base Properties of Nitrogen Heterocycles10m
- Reactions of Pyrrole, Furan, and Thiophene13m
- Directing Effects in Substituted Pyrroles, Furans, and Thiophenes16m
- Addition Reactions of Furan8m
- EAS Reactions of Pyridine17m
- SNAr Reactions of Pyridine18m
- Side-Chain Reactions of Substituted Pyridines20m
- 28. Carbohydrates5h 53m
- Monosaccharide20m
- Monosaccharides - D and L Isomerism9m
- Monosaccharides - Drawing Fischer Projections18m
- Monosaccharides - Common Structures6m
- Monosaccharides - Forming Cyclic Hemiacetals12m
- Monosaccharides - Cyclization18m
- Monosaccharides - Haworth Projections13m
- Mutarotation11m
- Epimerization9m
- Monosaccharides - Aldose-Ketose Rearrangement8m
- Monosaccharides - Alkylation10m
- Monosaccharides - Acylation7m
- Glycoside6m
- Monosaccharides - N-Glycosides18m
- Monosaccharides - Reduction (Alditols)12m
- Monosaccharides - Weak Oxidation (Aldonic Acid)7m
- Reducing Sugars23m
- Monosaccharides - Strong Oxidation (Aldaric Acid)11m
- Monosaccharides - Oxidative Cleavage27m
- Monosaccharides - Osazones10m
- Monosaccharides - Kiliani-Fischer23m
- Monosaccharides - Wohl Degradation12m
- Monosaccharides - Ruff Degradation12m
- Disaccharide30m
- Polysaccharide11m
- 29. Amino Acids3h 20m
- Proteins and Amino Acids19m
- L and D Amino Acids14m
- Polar Amino Acids14m
- Amino Acid Chart18m
- Acid-Base Properties of Amino Acids33m
- Isoelectric Point14m
- Amino Acid Synthesis: HVZ Method12m
- Synthesis of Amino Acids: Acetamidomalonic Ester Synthesis16m
- Synthesis of Amino Acids: N-Phthalimidomalonic Ester Synthesis13m
- Synthesis of Amino Acids: Strecker Synthesis13m
- Reactions of Amino Acids: Esterification7m
- Reactions of Amino Acids: Acylation3m
- Reactions of Amino Acids: Hydrogenolysis6m
- Reactions of Amino Acids: Ninhydrin Test11m
- 30. Peptides and Proteins2h 42m
- Peptides12m
- Primary Protein Structure4m
- Secondary Protein Structure17m
- Tertiary Protein Structure11m
- Disulfide Bonds17m
- Quaternary Protein Structure10m
- Summary of Protein Structure7m
- Intro to Peptide Sequencing2m
- Peptide Sequencing: Partial Hydrolysis25m
- Peptide Sequencing: Partial Hydrolysis with Cyanogen Bromide7m
- Peptide Sequencing: Edman Degradation28m
- Merrifield Solid-Phase Peptide Synthesis18m
- 32. Lipids 2h 50m
- 34. Nucleic Acids1h 32m
- 35. Transition Metals5h 33m
- Electron Configuration of Elements45m
- Coordination Complexes20m
- Ligands24m
- Electron Counting10m
- The 18 and 16 Electron Rule13m
- Cross-Coupling General Reactions40m
- Heck Reaction40m
- Stille Reaction13m
- Suzuki Reaction25m
- Sonogashira Coupling Reaction17m
- Fukuyama Coupling Reaction15m
- Kumada Coupling Reaction13m
- Negishi Coupling Reaction16m
- Buchwald-Hartwig Amination Reaction19m
- Eglinton Reaction17m
Alkene Stability - Online Tutor, Practice Problems & Exam Prep
Not all alkenes were created equal. Like carbocations, alkenes are stabilized through a phenomenon called hyperconjugation.
Hyperconjugation allows adjacent -R groups (mostly C-C and C-H σ-bonds) to create shared molecular orbitals with π-bonds, stabilizing the bond.
Understanding trends of alkene stability.
Video transcript
So basically, the more –R groups attached to the double bond, the more stable the double bond will be.
Specifically, when it comes to di-substituted bonds, the order os stability is gem > trans > cis.
- trans > cis due to steric hindrance. Groups have less freedom of movement in the cis position.
- gem > trans due to better hyperconjugation. The full explanation for this trend is beyond the level of this course. Just memorize it.
Rank the following alkenes in order of lowest to highest heat of combustion.
Heat of Combustion
Video transcript
Alright, so the first place we needed to start was figuring out what is lowest to highest heat of combustion. So remember earlier when we talked about heat of combustion, what heat of combustion has to do with is it's a measure of energy. So if you have a high heat of combustion, a high enthalpy, then what that means is that you have high energy. If you have high energy, that means you have low stability. So if it's saying here in order of lowest to highest heat of combustion, that means I want to start with the lowest, which is going to be the most stable, and end with the highest, which is going to be the least stable. Does that make sense? So even before this question began, there was a little bit of thinking that you needed to do. Now that we have that figured out, let's go ahead and order these guys. So we know that there's definitely going to be a winner here and that winner is going to be number 1. Why is that? Because if we identify the types of substituted double bonds we have, this one is trisubstituted because my double bond doesn't count and it has 3 branches coming off of it. 1, 2, 3. So, 3 yellow things. Let's just call it like that, really easy. Okay? 2 is going to be monosubstituted. Why? Because if I circle a double bond, I'm not including that, I only have one branch coming off of it, so one yellow area. So that would be mono. We know that's not going to be very good. This one would be disubstituted because I have 2 branches, 1, 2 di. And then this one would also be... oops, I did that wrong. This one would also be disubstituted because I have 2 branches, one here and one here. So now all I have to do is I have to figure out which of these is the most stable and which of these is the least. I know the most stable is going to be number 1 because that's trisubstituted. And I also know that the least stable is going to be number 2 because that one is monosubstituted. The hard part comes between numbers 3 and 4 because both of these are disubstituted. So how do I tell which one is better? The one that's better is going to be the one that is geminal and the one that's worse is going to be the one that is cis. Because for the cis one, both of my groups are facing the same side of the double bond, so that's really bad. For the geminal, they're facing on the same carbon, which is actually good. So what that means is that 3 is going to be more stable than 4, but still, 4 is going to be more stable than 2 because 4 is actually disubstituted and 2 is only monosubstituted. So in that case, cis is better than cis... disubstituted is better than just monosubstituted. Alright guys, so that's a really basic concept. This is an easy question on your exam. Most likely you will get a question like this. So this should be 3 points for you guys. Alright? Hope that made sense. Let's go ahead and move on to the next topic.
Do you want more practice?
More setsHere’s what students ask on this topic:
Your Organic Chemistry tutors
- Rank the following compounds from most stable to least stable: trans-3-hexene, cis-3-hexene, cis-2,5-dimethyl...
- The energy difference between cis- and trans-but-2-ene is about 4 kJ/mol; however, the trans isomer of 4,4-dim...
- For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be l...
- Explain why each of the following alkenes is stable or unstable. a. 1,2-dimethylcyclopentene b. trans-1,2-dime...
- A double bond in a six-membered ring is usually more stable in an endocyclic position than in an exocyclic pos...
- Using [TABLE 7-2] as a guide, predict which member of each pair is more stable, as well as by about how many ...
- Which species in each pair is more stable? f.
- Which species in each pair is more stable? a.CH3C−HCH2CH3 or CH3CH2CH2C−H2
- Conjugated dienes, molecules containing two alkenes separated by one single bond, are discussed in detail in C...
- Conjugated dienes, molecules containing two alkenes separated by one single bond, are discussed in detail in C...
- (••••) LOOKING AHEAD Bromination of buta-1,3-diene with a single equivalent of Br₂ can give either of two pro...
- Rank each group of compounds in order of increasing heat of hydrogenation. (b)
- Rank each group of compounds in order of increasing heat of hydrogenation. (a) hexa-1,2-diene; hexa-1,3,5-tri...
- (•••) When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stabl...
- (•••) LOOKING AHEAD Consider the Cope rearrangement, a reaction we describe in Chapter 20. (a) Using the knowl...
- Rank the following alkenes in order of stability ( 1 = most stable; 5 = least stable ). Explain your order. ...
- The same alkane is obtained from the catalytic hydrogenation of both alkene A and alkene B. The heat ofhydroge...
- a. Which is the most stable: 3,4-dimethyl-2-hexene, 2,3-dimethyl-2-hexene, or 4,5-dimethyl-2-hexene?b. Which c...
- Of the compounds you named in Problem 45:a. Which is the most stable?a. <IMAGE>b. <IMAGE>c. <IM...
- Of the compounds you named in Problem 45:b. Which is the least stable?a. <IMAGE>b. <IMAGE>c. <I...
- Which species in each pair is more stable?c. C−H2CH2CH═CH2 or CH3C−HCH═CH2d. <IMAGE>
- Use the data in [TABLE 7-2] <IMAGE> to predict the energy difference between 2,3-dimethylbut-1-ene and 2...
- Explain why each of the following alkenes is stable or unstable.h. <IMAGE>i. <IMAGE>
- For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be l...
- For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be l...
- In 1935, J. Bredt, a German chemist, proposed that a bicycloalkene could not have a double bond at a bridgehea...