Rank the following alcohols from strongest to weakest acid. CH 2 ═CHCH 2 OH; CH 3 CH 2 CH 2 OH; HC≡CCH 2 OH

Hey everyone. And welcome back in today's video, we're going to rank these compounds in order of increasing acidity. Now, we're given three structures, we control the bond line representation of the first one which has four carbon atoms, 1234 and an alcohol group bonded to carbon number one. Now the second one has five carbon atoms in the parents. So that's 12345 and an alcohol group bonded to carbon number one. And finally, the third one has a triple bond. But before we move on to the third one, let's just add our double bonds. The second one which starts at carbon number two. So now, similarly for the 3rd 1, let's add our triple bond. We noticed that our carbon is bonded to cease to group, which is bounded to O H. And then on the other hand, we have two carbon atoms. So that's our ethyl group on the left. Now, the three alcohols are pretty much similar in their structures. Of course, there is a slight difference that the first structure only has four carbon atoms and the second one and the third one, they have five carbon atoms in the parent, that's however not, not so important. The main importance is the fact that in the first structure, we have SP three hybridized carbon atoms. So let's just think about the first and the second one. For the second structure, we have an sp three carbon followed by an SP two. And there's another sp two right now for the third structure, we have an SP three hybridized carbon followed by an S P. And then we have another SP remember that if you only have carbon atom that has four single bonds, it's sp three hybridized, right? We have implicit hydrants, double bonded carbons are SP two triple bonded once R S P. And this is actually the aspect that we want to analyze. Remember that electro negativity of carbon increases. Using the following trend, sp carbon atoms are more electro negative than SP two and SP two carbons are more electro negative than SP three. And similarly, this trend also applies to acidity, right? Because more electro negative carbon atoms are more electron withdrawing and therefore weakening our O H bond. So that that means acidity will increase from right to left. So acidity increases from rights left, meaning sp three structure will be least acidic followed by SP two and SP will be the most acidic. Now, the reason for that is if you think about it, whenever we have an O H bond, the structure becomes more acidic whenever it's easier for us to break that O H bond and release hydrogen in the form of a proton into solution. And the weights weaken that bond is to withdraw electrons from that O H bond. If we have an adjacent S P carbon, for example, which is strongly electron withdrawing compared to SP three, it's essentially weakening the O H bond and it's making that hydrogen more acidic. So in each structure, the most acidic hydrogen is apparently hydrogen that is bonded to oxygen because its bond is the most electro negative atom. And as we said, sp hybridization will allow to weaken that bond the most. So if we want to rank our compounds of increasing acidity, we will start with the structure or basically the alcohol that only has SP three carbons. So let's add it. That's our first structure or the first alcohol, which is the weakest asset followed by the alcohol which contains SP two hybridized carbon atoms, right? Because they're more electro negative than SP three and therefore weakening our O H bond more. So let's add that structure. And finally, the most acidic one will correspond to our alkaline or basically our alcohol which contains a triple bond. So let's add that right. And we got our trend, the least acidic alcohol is the one that contains SP three carbons only followed by the alcohol that contains a double bond, right? Because these two carbon atoms are more electro negative than SP three ones and their electron withdrawing and weakening the O H bond followed by the most acidic one which contains a triple bond because sp hybridized carbon atoms are the most electro negative and therefore weakening the O H bond the most. So this is our trend. And based on our answer, we may conclude that the correct answer to the multiple choice question is c thank you for watching.

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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

3. Acids and Bases

Ranking Acidity

Organic Chemistry

3. Acids and Bases

Ranking Acidity

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5:39 minutes

Problem 62a

Textbook Question

Rank the following alcohols from strongest to weakest acid.
CH₂═CHCH₂OH; CH₃CH₂CH₂OH; HC≡CCH₂OH

Verified step by step guidance

Step 1: Recall that the acidity of alcohols is influenced by the stability of the conjugate base formed after deprotonation. A more stable conjugate base corresponds to a stronger acid.

Step 2: Analyze the conjugate bases of the given alcohols. For CH2═CHCH2OH, the conjugate base is CH2═CHCH2O⁻. The presence of the vinyl group (CH2═CH-) can stabilize the conjugate base through resonance effects.

Step 3: For CH3CH2CH2OH, the conjugate base is CH3CH2CH2O⁻. This is a simple alkoxide ion without any resonance or inductive effects to stabilize it, making it less stable compared to the conjugate base of CH2═CHCH2OH.

Step 4: For HC≡CCH2OH, the conjugate base is HC≡CCH2O⁻. The presence of the alkyne group (HC≡C-) can exert an inductive effect, pulling electron density away from the oxygen atom and stabilizing the conjugate base.

Step 5: Rank the alcohols based on the stability of their conjugate bases: HC≡CCH2OH (strongest acid due to inductive effect) > CH2═CHCH2OH (moderate acid due to resonance stabilization) > CH3CH2CH2OH (weakest acid due to lack of stabilization).

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Key Concepts

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

Acidity of Alcohols

The acidity of alcohols is determined by the stability of their conjugate bases after deprotonation. Alcohols can donate a proton (H+) to form an alkoxide ion, and the more stable the alkoxide, the stronger the acid. Factors influencing acidity include the electronegativity of the atoms attached to the hydroxyl group and the overall molecular structure.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on a molecule. In alcohols, electron-withdrawing groups can stabilize the negative charge on the conjugate base, enhancing acidity. For example, alkyl groups are electron-donating, which can decrease acidity, while groups like halogens can increase it.

Hybridization and Acidity

The hybridization of the carbon atom bonded to the hydroxyl group affects the acidity of alcohols. sp-hybridized carbons (like in HC≡CCH2OH) are more electronegative than sp2 or sp3 hybridized carbons, leading to a more stable conjugate base. Thus, alcohols with sp-hybridized carbons tend to be stronger acids compared to those with sp2 or sp3 hybridization.

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