(a)
Interpretation:
It is to be explained why the pKa values of all three isomers in which a methyl group is attached to the ring are higher than the pKa of phenol itself.
Concept introduction:
When comparing uncharged acids, the stronger acid is the one whose negatively charged conjugate base is more stable. Electron donating substituents attached to the ring decrease the acidity as compared to non-substituted rings. Alkyl group is an electron donating group, thus, it will destabilize the negatively charged conjugate base to a greater extent than non-substituted rings.
(b)
Interpretation:
Why the meta isomer has the lowest
Concept introduction:
When comparing uncharged acids, the stronger acid is the one whose negatively charged conjugate base is more stable. Electron donating substituents attached to the ring decrease the acidity as compared to non-substituted rings. Methyl groups is an electron donating group, thus, it will destabilize the negatively charged conjugate base to a greater extent than non-substituted rings. Greater the resonance stabilization of the conjugate base, stronger is the acid. In the resonance contributors, the structure in which an atom bearing a negative charge becomes destabilized as the number of electron-donating groups attached to it increases. This structure will not contribute significantly to the resonance hybrid.
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Chapter 6 Solutions
Organic Chemistry: Principles and Mechanisms (Second Edition)
- Provide an explanation without using the pka values : Why is phenol stronger acid than butanoic acid?arrow_forwardWhich compound in each pair is more basic: (a) (CH3)2NH and NH3; (b) CH3CH2NH2 and ClCH2CH2NH2?arrow_forwardPhthalic acid and isophthalic acid have protons on two carboxy groups that can be removed with base. (a) Explain why the pKa for loss of the rst proton (pKa1) is lower for phthalic acid than isophthalic acid. (b) Explain why the pKa for loss of the second proton (pKa2) is higher for phthalic acid than isophthalic acid.arrow_forward
- Provide the approximate pK, of the following and indicate the most acidic hydroge (a) CH3-NH-CH3 (b) CH3-C=CH (c) CH3-COOH (d) CH3-CH2-OHarrow_forwardNepheliosyne B is a novel acetylenic fatty acid isolated from a New Caledonian marine sponge. (a) Label the most acidic H atom. (b) Which carbon–carbon σ bond is shortest? (c) How many degrees of unsaturation does nepheliosyne B contain? (d) How many bonds are formed from Csp–Csp3? (e) Label each triple bond as internal or terminal.arrow_forwardThe pka of phenol (C6H5OH) is 10.0. When a nitro group (NO2) is attached to the ring, the pK, decreases, as shown for the ortho, meta, and para isomers. OH OH ОН OH NO2 (a) Explain why the pK, values of all three isomers are lower than the pka of phenol itself. (b) Explain why the meta isomer has the highest pka of `NO2 Phenol NO2 the three isomers. pKa = 10.0 7.23 8.35 7.14arrow_forward
- но HO но он The pK, of ascorbic acid (vitamin C) is 4.17, showing that it is slightly more acidic than acetic acid (CH3CO0H, pKa 4.74). (a) Show the fou r different conjugate bases that would be formed by deprotonation of the four different OH groups in ascorbic acid. (b) Compare the stabilities of these four conjugate bases, and predict which OH group of ascorbic acid is the most acidic. (c) Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH) group.arrow_forwarda If an acid, HA, dissolves in water such that the Ka is 10000, what is the pK, of that acid? pK :arrow_forward(a) Explain how NaBH, in CH;OH can reduce hemiacetal A to 1,4-butanediol (HOCH,CH,CH,CH,OH). (b) What product is formed when A is treated with Ph;P=CHCH,CH(CH),? (c) The drug isotretinoin is formed by reaction of X and Y. What is the structure of isotretinoin? Although isotretinoin (trade name Accutane or Roaccutane) is used for the treatment of severe acne, it is dispensed under strict controls because it also causes birth defects. PPha NaOCH,CH3 HO- isotretinoin HO A Br X Yarrow_forward
- Match each of the following pk, values (3.2, 4.9, and 0.2) to the appropriate carboxylic acid: (a) CH;CH,COOH; (b) CF3COOH; (c) ICH;COOH.arrow_forwardPhthalic acid and isophthalic acid have protons on two carboxy groupsthat can be removed with base. (a) Explain why the pKa for loss of thefirst proton (pKa1) is lower for phthalic acid than isophthalic acid. (b)Explain why the pKa for loss of the second proton (pKa2) is higher forphthalic acid than isophthalic acid.arrow_forwardPQ-27. What is the product of this reaction? (A) 0 OH a (B) (D) H₂ Ptarrow_forward