Alcohols, Phenols and Ethers — MHT-CET Chemistry Formulas and Traps

Classification of Alcohols and Phenols

Allylic, Benzylic and Vinylic Alcohols, and 1°/2°/3°

Two labels on the OH carbon

\text{degree: } 1^\circ/2^\circ/3^\circ \text{ by carbons attached};\quad \text{allylic: C=C next door};\ \text{benzylic: ring next door};\ \text{vinylic: OH on C=C}

Molecular Formula and the Preparations of Alcohols

The two hydrations

\text{RCH=CH}_2 \xrightarrow{\text{B}_2\text{H}_6;\ \text{H}_2\text{O}_2/\text{OH}^-} \text{RCH}_2\text{CH}_2\text{OH};\qquad \text{RCH=CH}_2 \xrightarrow{\text{H}_2\text{SO}_4;\ \text{H}_2\text{O}} \text{RCH(OH)CH}_3

Monohydric, Dihydric, Trihydric: the Named Diols and Phenols

Compound	OH count	Class	Note
Crotonyl (crotyl) alcohol	1	Monohydric, allylic	Not dihydric despite the C=C
Ethylene glycol	2	Dihydric alcohol	Intramolecular H-bond
Catechol / resorcinol / quinol	2	Dihydric phenols	1,2 / 1,3 / 1,4 — isomers of each other Resorcinol is the isomer of catechol the paper keys.
Glycerol (propylene glycerol)	3	Trihydric alcohol	Propane-1,2,3-triol
Pyrogallol / phloroglucinol	3	Trihydric phenols	1,2,3 / 1,3,5 Phloroglucinol is NOT dihydric.
Ascorbic acid	—	Not a phenol	No OH on a benzene ring

Dihydric means two OH; the benzenediols are each other's isomers.

Common traps

Calling but-3-en-1-ol allylic

Count the bonds: OH carbon → CH₂ → CH=. Two carbons away is homoallylic, not allylic. Allylic means the OH carbon is bonded directly to a double-bond carbon.

Reading '-ol' endings as OH counts

Phloroglucinol ends like a diol but has three OH groups; pyrogallol too. Count from the structure or the IUPAC name (benzene-1,3,5-triol), never from the common name.

Putting the OH on the wrong carbon in hydroboration

Hydroboration is the ANTI-Markovnikov route: boron, then OH, goes to the less substituted carbon. But-1-ene gives butan-1-ol, not butan-2-ol — the acid route gives that.

IUPAC and Common Nomenclature of Alcohols, Phenols and Ethers

Learn this subtopic in the notes

Carbinol Names and the Butyl Alcohols

Carbinol rule

\text{R}_1\text{R}_2\text{R}_3\text{C-OH} \to \text{(R}_1\text{ R}_2\text{ R}_3\text{) carbinol, alphabetical}

IUPAC Names From a Drawing: Ring Alcohols, Ring Ethers, Alkenols

Locant rules

\text{OH carbon} = \text{C1} \to \text{lowest locant SET for substituents} \to \text{alphabetical tie-break}

Isomer Pairs: Alcohol–Ether, Position, Metamers

Same formula, or no isomerism

\text{C}_4\text{H}_{10}\text{O}: \text{ butanols (alcohol)} \leftrightarrow \text{ethoxyethane / methoxypropane (ethers)}

The Named Phenols: Common Name ↔ IUPAC Name

Common name	IUPAC name	OH positions
Catechol	Benzene-1,2-diol	ortho
Resorcinol	Benzene-1,3-diol	meta
Quinol (hydroquinone)	Benzene-1,4-diol	para
Pyrogallol	Benzene-1,2,3-triol	adjacent three 1,2,3 — not 1,3,5.
Phloroglucinol	Benzene-1,3,5-triol	alternate three
o-Cresol	2-Methylphenol	OH + CH₃ ortho The planted wrong pairing is 'o-cresol : benzene-1,2,3-triol'.
Glycerol	Propane-1,2,3-triol	—

Diols: cat-ortho, res-meta, quin-para. Triols: pyro-1,2,3, phloro-1,3,5.

Common traps

Naming isobutyl alcohol 'isobutyl carbinol'

The carbinol carbon is the CH₂OH; what hangs on it is an ISOPROPYL group. Isobutyl carbinol would be a five-carbon alcohol.

Swapping pyrogallol and phloroglucinol

Both are triols. Pyrogallol's three OH are ADJACENT (1,2,3); phloroglucinol's alternate (1,3,5). The two are always offered together.

Numbering the ring the short way

Going from C1 towards the methyl gives 2-methyl-5-ethyl — same locant set, wrong alphabetical order. The 2023 paper keyed 2-ethyl-3-methyl for a drawing with the groups on the same side and 2-ethyl-5-methyl for one with them on opposite sides; look at the drawing, not the option you remember.

Assuming any two ethers are metamers

Metamers must share a molecular formula. Methoxyethane (C₃) and ethoxyethane (C₄) differ by a CH₂ — homologues, not isomers of any kind.

Physical Properties of Alcohols, Phenols and Ethers

Learn this subtopic in the notes

Boiling Points: H-Bonding, Chain Length, Branching

Boiling-point levers

\text{H-bonding} \uparrow,\ \text{chain length} \uparrow \Rightarrow \text{b.p.} \uparrow;\qquad \text{branching} \uparrow \Rightarrow \text{b.p.} \downarrow

Solubility in Water and the Kinds of Hydrogen Bond

Solubility order

\text{R-OH} > \text{R-NH}_2 > \text{R-H} \quad (\text{H-bonding with water decides})

p-Nitrophenol Melts Highest: Inter- Versus Intramolecular H-Bonds

Which H-bond

\text{ortho: intramolecular} \Rightarrow \text{low m.p., volatile};\qquad \text{para: intermolecular} \Rightarrow \text{high m.p.}

Common traps

Ranking iso-butyl above sec-butyl

The measured values put isobutyl (108 °C) above sec-butyl (100 °C), but the paper's keyed order is n > sec > iso > tert — 'branching lowers boiling point' counted by the position of the branch. Give the paper's order; the endpoints (n highest, tert lowest) are never in doubt.

Ranking the amine above the alcohol

N–H···O bonds are weaker than O–H···O. Amines dissolve, but less than alcohols of the same size. The alkane, with no H-bonding, is always last.

Picking o-nitrophenol for the highest melting point

Its hydrogen bond is INSIDE the molecule and does nothing to hold molecules together. p-Nitrophenol, whose OH must bond to a neighbour, melts almost 70 °C higher.

Chemical Reactions of Alcohols and Acidity

Learn this subtopic in the notes

Lucas Reagent and the HX Reactivity Order

Lucas test

\text{R-OH} \xrightarrow{\text{conc. HCl / ZnCl}_2} \text{R-Cl}\ (\text{turbid});\quad 3^\circ \text{ instant} > 2^\circ \text{ minutes} > 1^\circ \text{ none}

Dehydration (Saytzeff, With Rearrangement) and Oxidation

Dehydration

\text{R}_2\text{CH-CH(OH)R} \xrightarrow{\text{conc. H}_2\text{SO}_4,\ \Delta} \text{R}_2\text{C=CHR} + \text{H}_2\text{O} \quad (\text{Saytzeff, after any hydride shift})

Alcohols From Grignard Reagents; Acidity of Alcohols and Phenols

Grignard to alcohol

\text{HCHO} \to 1^\circ;\quad \text{RCHO} \to 2^\circ;\quad \text{R}_2\text{CO} \to 3^\circ \quad (\text{then H}_3\text{O}^+)

Common traps

Marking esterification as C–O cleavage

In R–OH + R'COOH the alcohol keeps its oxygen (the ester is R'CO–O–R); it is the O–H bond that breaks. C–O breaks only when the whole OH leaves — HX, PX₃, SOCl₂, dehydration.

Eliminating from the carbon that carried the OH

The secondary cation rearranges before it loses a proton. Hex-3-ene from 2-methylhexan-3-ol is the drawing beside the right answer; the hydride shift moves the double bond to the branched carbon.

Counting the Grignard carbon into the wrong place

3-Methylpentan-3-ol has C3 bearing OH, methyl, ethyl, ethyl. One ethyl came from the Grignard, so the ketone had methyl + ethyl on the carbonyl: butanone, not propanone.

Phenols: Preparation and Reactions

Learn this subtopic in the notes

Making Phenol: Cumene and Dow

Cumene route

\text{C}_6\text{H}_5\text{CH(CH}_3)_2 \xrightarrow{\text{O}_2} \text{C}_6\text{H}_5\text{C(CH}_3)_2\text{OOH} \xrightarrow{\text{H}^+} \text{C}_6\text{H}_5\text{OH} + (\text{CH}_3)_2\text{CO}

Nitration and Bromination of Phenol

How far the reaction goes

\text{dil. HNO}_3 \to o/p\text{-nitrophenol};\quad \text{HNO}_3/\text{H}_2\text{SO}_4 \to \text{picric acid};\quad \text{Br}_2(\text{aq}) \to 2,4,6\text{-tribromophenol}

Kolbe, Reimer–Tiemann, Oxidation and Reduction of Phenol

Kolbe and Reimer–Tiemann

\text{ArONa} + \text{CO}_2 \to o\text{-HOC}_6\text{H}_4\text{COONa} \to \text{salicylic acid};\qquad \text{ArOH} + \text{CHCl}_3/\text{NaOH} \to o\text{-HOC}_6\text{H}_4\text{CHO}

Phenols in Nature: Eugenol, Gallic Acid, Curcumin and the Polyols

Phenol	Source	Property / use
Eugenol	Clove	Analgesic and antimicrobial Not 'antiseptic' alone — the paper keys the analgesic-and-antimicrobial pair.
Gallic acid	Indian gooseberry (amla), gall nuts	Antioxidant
Curcumin	Turmeric	Antioxidant, anti-inflammatory
Methyl salicylate	Wintergreen	Liniment
Ascorbic acid	Citrus fruits	Vitamin C — NOT a phenol No OH on a benzene ring.

Source and use are asked in both directions.

Common traps

Stopping at cumene hydroperoxide

The hydroperoxide is the intermediate; the question asks for the products after dilute acid — phenol AND acetone, both of them, which is why the process pays.

Trinitrating with dilute acid

Dilute HNO₃ gives the mononitro mixture; 2,4,6-trinitrophenol needs the mixed acid. Bromine is the opposite case — WATER gives the tri-substituted product, the organic solvent the mono.

Starting Kolbe from phenol itself

The substrate is SODIUM PHENOXIDE — the phenoxide ion is what attacks CO₂. 'Phenol' is offered as option (a) and is wrong.

Confusing the 1,2,3 and 1,3,5 triol drawings

Phloroglucinol is the SYMMETRIC one — OH at alternate carbons. Three OH in a row is pyrogallol; the paper draws both and asks for one.

Ethers: Preparation and Reactions

Learn this subtopic in the notes

Williamson Synthesis: Alkoxide Plus Primary Halide

Williamson synthesis

\text{R-O}^-\text{Na}^+ + \text{R'-X} \xrightarrow{\text{SN2}} \text{R-O-R'} + \text{NaX} \quad (\text{R'X primary; never aryl})

Reactions of Ethers: Oxonium Salts, HI Cleavage, Anisole

Cleavage by HI

\text{Ar-O-R} + \text{HI} \xrightarrow{\Delta} \text{Ar-OH} + \text{R-I} \quad (\text{aryl-O bond survives})

Common traps

Expecting isobutylene from methyl bromide and tert-butoxide

Elimination needs a β-hydrogen on the HALIDE; methyl bromide has none. The bulky base simply attacks the unhindered methyl carbon: MTBE forms.

Cleaving the aryl side with HI

The aryl–oxygen bond has partial double-bond character and does not break. Anisole gives phenol + CH₃I; 'iodobenzene + methanol' is the planted option.

Alcohols, Phenols and Ethers formulas

Classification of Alcohols and Phenols

Allylic, Benzylic and Vinylic Alcohols, and 1°/2°/3°

Molecular Formula and the Preparations of Alcohols

Monohydric, Dihydric, Trihydric: the Named Diols and Phenols

Common traps

IUPAC and Common Nomenclature of Alcohols, Phenols and Ethers

Carbinol Names and the Butyl Alcohols

IUPAC Names From a Drawing: Ring Alcohols, Ring Ethers, Alkenols

Isomer Pairs: Alcohol–Ether, Position, Metamers

The Named Phenols: Common Name ↔ IUPAC Name

Common traps

Physical Properties of Alcohols, Phenols and Ethers

Boiling Points: H-Bonding, Chain Length, Branching

Solubility in Water and the Kinds of Hydrogen Bond

p-Nitrophenol Melts Highest: Inter- Versus Intramolecular H-Bonds

Common traps

Chemical Reactions of Alcohols and Acidity

Lucas Reagent and the HX Reactivity Order

Dehydration (Saytzeff, With Rearrangement) and Oxidation

Alcohols From Grignard Reagents; Acidity of Alcohols and Phenols

Common traps

Phenols: Preparation and Reactions

Making Phenol: Cumene and Dow

Nitration and Bromination of Phenol

Kolbe, Reimer–Tiemann, Oxidation and Reduction of Phenol

Phenols in Nature: Eugenol, Gallic Acid, Curcumin and the Polyols

Common traps

Ethers: Preparation and Reactions

Williamson Synthesis: Alkoxide Plus Primary Halide

Reactions of Ethers: Oxonium Salts, HI Cleavage, Anisole

Common traps

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