Question

Which of the following alcohols is the least acidic? ОН OH OH OH 00 or а. NO2 b. OH C. Select one: a. Structure c b. Structure a c. Structure b d. Structured

Answer 1

Electron withdrawing groups like -NO2 ( Nitro) etc , increases the acidic strength by stabilizing the Phenoxide ion.

While electron donating groups like -R ( alkyl ) , -OH etc decreases acidic strength by increasing electron density on phenoxide ion ( which makes phenoxide ion less stable ).

So least acidic alcohol will be option d. structure d ( p-Cresol) due to +I ( inductive effect) as well as Hyperconjugation effect. It has pKa value 10.14

For detailed solution and explanation, please refer to the images attached below.

OH Phenol :O-H tiöka (aq) + Hot Phenoxide Jon Ht/H2O ou The Acidity of the hal is due to release of Hoot (Proton). Now: - The Phonoxide ion is also retabilize by resonance. * Effect of substituents on the Acidity of Phenols: The Acidity of Phenals is due to the Greater resonance stabilization of the frenoxide ion relative to Phenal. Therefore, any substituent which stabilizes the Phenoxide ion more by dispersal of Negative charge will tend to Increase the Acidity of Phonals. Conversely, any substituent which destabilizes the Phenoxide ion relative to Phanel by intensifying its negative charge will decrease the audity of Phenols,

etc. which destabilize the Phenoxide © Electron- with drawing groups (Ewa) like -NO2,-(N, X ( Halogen) etc. which Stabilize the phenoxide jon by disbursing the Negative change relative to Phenal increases the audie strength of Phenoles он OH -H₂O Ewq. Ew4. Electron - withdrawing group (Ewa) with draws ele tohous, dis fortes the Negative charge, stabilizes the phenoxide ion with respect to prenul And thus increases the auid strength OH OM So is more acidic than H As Nog Critro) group Has Electron withdrawing effect. ® Ek dron- dovuting groups (E-9.4.) Slike -NH2, -OR [Alkong) jen by intowsifying the Negative charge relative to Phonel tend to decrease the acidic strength of Phenols.

он Hao EDGE Electron-donating group (ED4) donates electrons, Intensifies the negative charge, destabilizes the phenoxide ion with respect to Phenal and thus decreases the and strength. E14. -OH CH3 >> These two are electron donating Groups so they will decreases Acidic Strength OH PH So and are less Audic than Promul он So Correct onder of Acidre strength will be as: - It is leust Audio OH ol Most. while Nog Due to th effect fka =7.15 and Hyber conjugation Effect

OH It is Least Acidic al stenetured ! Q.2, group is attached to a Primary (1), Secondary (20) And Tertiary (3) alcohols are classified According as the LOH Primary secondary and tertiary carbon atoms respectively go (secondary) Alcofielg; - In these alcopals, the Hydroxyl groute is attached with Secondary (29) Carbon atom. They possess CHOH and be same on different characteristic groups CR and Ål may General formula R-CHOM R Alltyl groupe)

A. g- methyl-2-bentanal OH H₃C-(-(-(-CH₃ H₂ H₂ 1 CH3 30 ( Tertiary Alcohol) B. 2- Ethyl-1-pentanal H He HL HO-C-(-EC-CH3 p (primary Alcohol) 1 H Cats 4-methyl-3-heptanol y H₃ C-(-(-(-(-(-CH3 Hg II 12 Ma OH CH₃ go (secondary Alcopal 3-methyl-2- $ Entanal sh И (-(-(-(-CH3 go (Secondary Alcohel) ANSWER C And D options. CH3