31 Year NEET Previous Year Questions: Alcohols, Phenols & Ethers - NEET MCQ

Glycol is used as an antifreeze in automobiles.

Glycerol when treated with excess HI produces  2–iodopropane

∴ Correct choice : (b)

The presence of electron withdrawing substituent increases the acidity while electron releasing substituent, when present, decrease the acidity.
Phenyl is an electron withdrawing substituent while -CH₃ is an electron releasing substituent, Moreover, phenoxide ion is more resonance stabilised as compared to benzoyl oxide ion, thus, release proton more easily. That's why is a strong acid among the given.

(– I and – M effects, (only – I effect) both increase acidity)

(+ I effect of CH₃ group decreases acidity)
∴ Correct choice : (b)

1, 2 – Diols, when treated with an aqueous solution of periodic acid give aldehyde or ketones

Note that a 1° alcohol gives CH₂O. Since in glycol both the OH groups, are primary hence give 2 molecules of CH₂O as by product.

Ethylene oxide when treated with Grignard Reagent gives primary alcohol.

First HI will break into H+ and I-. Then H+ attacks on ether to form CH₃O⁺HCH(CH₃)₂
Being an excellent nucleophile, I- attacks where it is easy to attack and so it will go for less bulky CH₃ to form CH₃I and (CH₃)₂CHOH.

CH₃OH does not have -CH(OH)CH₃ grouping hence it will not form yellow precipitate  with an alkaline solution of iodine (haloform reaction).

Primary alcohol on oxidation give aldehyde which on further oxidation give carboxylic acid whereas secondary alcohols give ketone.

Hence C is correct.

The acidic nature of phenol is due to the formation of stable phenoxide ion in solution

The phenoxide ion is stable due to resonance.

The negative charge is delocalized in the benzene ring which is a stabilizing factor in the phenoxide ion and increase acidity of phenol. wheras no resonance is possible in alkoxide ions (RO^–)derived from alcohol. The negative charge is localized on oxygen atom.
Thus, alcohols are not acidic.

This is grignard reaction formation of 1-Phenylethanol 

takes place when benzaldehyde reacts with methyl iodide 

and magnesium followed by hydrolysis.

Due to –I-effect of the three C–Cl-bonding between CI and C-atom of the OH group, CCl₃ CH (OH)₂ is most stable.

1° Alcohols on catalytic dehydrogenation give aldehydes.

Secon dary alcoh ols on oxidation give ketones.
Note : – Primary alcohols from aldehydes.

Electron-donating groups (– OCH₃, – CH₃ etc.) tend to decrease and electron withdrawing groups (– NO₂, – OCH₃ etc.) tend to increase the acidic character of phenols. Since – OCH₃ is a more powerful electron-donating group than – CH₃ group, therefore, p-methylphenol is slightly more acidic than p-methoxyphenol while pnitrophenol is the strongest acid. Thus, option (d), i.e. p-methoxyphenol, pmethylphenol, p-nitrophenol is correct.

Due to H-bonding, the boiling point of ethanol is much higher than that of the isomeric diethyl ether.

With Br₂ water, phenol gives 2, 4, 6-tribromophenol.

Water gas is mixed with half of its volume of hydrogen.The mixture is compressed to approximately 200 – 300 atmospheres. It is then passed over a catalyst |ZnO + Cr₂O₃| at 300°C. Methyl alcohol vapours are formed which are condensed

Four primary alcohols of C₅H₁₁OH are possible. These are:

(i) CH₃CH₂CH₂CH₂CH₂OH

(ii)

(iii)

(iv)