Organic Reaction Mechanisms — JEE Mains Chemistry Formulas and Traps

Carbocations, Rearrangements and Addition Regiochemistry

Carbocation stability and 1,2-shifts

Carbocation stability order

3^\circ > 2^\circ > 1^\circ > \mathrm{CH_3^+} \qquad \text{benzylic and allylic cations: resonance-stabilised}

Addition regiochemistry by reagent

Reagent	Where the new group goes	Why	Example
HBr (no peroxide)	Br on the more substituted carbon	The more stable cation forms; it can rearrange	$\mathrm{(CH_3)_2C{=}CH_2 \to (CH_3)_3CBr}$
HBr with a peroxide	Br on the less substituted carbon	Free-radical chain; works for HBr only	$\mathrm{(CH_3)_2C{=}CH_2 \to (CH_3)_2CHCH_2Br}$
$\mathrm{H_2O}$ , dilute $\mathrm{H_2SO_4}$	OH on the more substituted carbon	Through a cation; it can rearrange	$\mathrm{(CH_3)_2C{=}CH_2 \to (CH_3)_3COH}$
$\mathrm{B_2H_6}$ , then $\mathrm{H_2O_2/OH^-}$	OH on the less substituted carbon	No cation: syn addition, no rearrangement	$\mathrm{(CH_3)_2C{=}CH_2 \to (CH_3)_2CHCH_2OH}$
$\mathrm{H_2O}$ , $\mathrm{Hg^{2+}/H_2SO_4}$ on an alkyne	O on the inner carbon; a ketone	Markovnikov enol changes to the keto form	$\mathrm{CH_3CH_2C{\equiv}CH \to CH_3CH_2COCH_3}$ Only ethyne gives an aldehyde (ethanal) this way.
$\mathrm{B_2H_6}$ , then $\mathrm{H_2O_2/OH^-}$ on a terminal alkyne	O on the end carbon; an aldehyde	Anti-Markovnikov enol changes to the aldehyde	$\mathrm{CH_3CH_2C{\equiv}CH \to CH_3CH_2CH_2CHO}$
$\mathrm{Br_2}$ in $\mathrm{CCl_4}$	One Br on each carbon, on opposite faces	Cyclic bromonium ion opened from the back	Cyclohexene gives trans-1,2-dibromocyclohexane
$\mathrm{Br_2}$ , $\mathrm{NaHCO_3}$ on an unsaturated acid	Ring O on the inner carbon, Br outside the ring	The molecule's carboxylate opens the bromonium ion	An alkenoic acid gives a bromo-lactone, a five-membered ring when possible

Through a cation: Markovnikov, and a shift is possible. Through boron or a radical: the other carbon, and no shift.

Common traps

A primary halide in Friedel-Crafts alkylation gives the branched product

The primary cation (or its complex with

\mathrm{AlCl_3}

) rearranges before it attacks the ring. 1-Chloropropane gives isopropylbenzene, not n-propylbenzene. To put a straight chain on a ring, acylate and then reduce the C=O.

No shift without a better cation at the end

A 1,2-shift happens only when the new cation is more stable. A tertiary cation, or a benzylic one next to a ring, has nothing better to reach, so its product is not rearranged.

Stability and rate go together

The more stable carbocation is also the one formed faster, because the transition state resembles the cation. An option that pairs 'more stable' with 'formed more slowly' is wrong.

Hydroboration puts OH on the less substituted carbon

\mathrm{B_2H_6}

followed by alkaline

\mathrm{H_2O_2}

is anti-Markovnikov: a terminal alkene gives a primary alcohol, which PCC can then take to an aldehyde. Acid hydration of the same alkene gives the secondary or tertiary alcohol.

The peroxide effect works for HBr only

With a peroxide, HBr adds anti-Markovnikov by a radical chain. HCl and HI still add by Markovnikov's rule with or without a peroxide.

Alkyne hydration ends at a carbonyl

The first product is an enol, which changes to its keto form at once. With

\mathrm{Hg^{2+}/H_2SO_4}

a terminal alkyne gives a methyl ketone; by hydroboration it gives an aldehyde. Neither route stops at an alcohol.

Carbonyl Reactions: Enolates, Haloform and Cannizzaro

Learn this subtopic in the notes

Aldol, Claisen-Schmidt, Claisen and Michael reactions

Claisen-Schmidt condensation and percentage yield

\mathrm{ArCHO + CH_3COR \xrightarrow{OH^-} ArCH{=}CHCOR + H_2O} \qquad \%\,\text{yield} = \dfrac{\text{actual mass}}{\text{theoretical mass}} \times 100

Haloform, Cannizzaro and decarboxylation

Haloform and Cannizzaro equations

\mathrm{RCOCH_3 + 3X_2 + 4NaOH \to RCOONa + CHX_3 + 3NaX + 3H_2O} \qquad \mathrm{2\,ArCHO + NaOH \to ArCH_2OH + ArCOONa}

Common traps

Acetone condenses on both sides

With excess aromatic aldehyde, both

\mathrm{CH_3}

groups of acetone react, so two moles of aldehyde make one mole of dibenzalacetone. Taking a 1:1 ratio doubles the theoretical yield and halves the percentage.

Benzaldehyde cannot form an enolate

Benzaldehyde has no α-hydrogen. In a crossed aldol it can only be attacked; with concentrated alkali and nothing else, it undergoes the Cannizzaro reaction instead.

Michael addition goes to the β-carbon

A soft nucleophile such as a thiolate adds to the carbon at the far end of the C=C, not to the C=O or the C≡N. Acrylonitrile,

\mathrm{CH_2{=}CHCN}

, gains the new group on its

\mathrm{CH_2}

.

The haloform reaction removes one carbon only

Only the

\mathrm{CH_3}

of the

\mathrm{CH_3CO}

group leaves, as

\mathrm{CHX_3}

. A methyl ketone with n carbons gives a carboxylate with n − 1 carbons; soda lime then removes one more.

Cannizzaro needs an aldehyde with no α-hydrogen

Ethanal or propanal in alkali forms an enolate and gives an aldol product, not a Cannizzaro mixture. Formaldehyde, benzaldehyde and 2,2-dimethylpropanal have no α-H and disproportionate.

In a crossed Cannizzaro, formaldehyde is oxidised

Formaldehyde is the most reactive aldehyde, so hydroxide adds to it first and it gives up the hydride. It ends as formate, and the other aldehyde ends as the alcohol.

Multistep Conversions and Road Maps

Learn this subtopic in the notes

Aromatic road maps: acylation, reduction and diazonium routes

Straight-chain alkylbenzene by acylation then reduction

\mathrm{C_6H_6 \xrightarrow{RCOCl,\ AlCl_3} C_6H_5COR \xrightarrow{Zn{-}Hg,\ HCl} C_6H_5CH_2R}

Carbon counting in chain-building steps

Reagent	Carbon count change	Group produced	Example
KCN on an alkyl halide	+1 for each halogen replaced	Nitrile; $\mathrm{H_3O^+}$ gives COOH, $\mathrm{H_2/Ni}$ gives $\mathrm{CH_2NH_2}$	$\mathrm{CH_3CH_2Br \to CH_3CH_2CN \to CH_3CH_2COOH}$
RMgX, then HCHO and $\mathrm{H_3O^+}$	+1 on R	Primary alcohol $\mathrm{RCH_2OH}$	$\mathrm{CH_3CH_2MgBr \to CH_3CH_2CH_2OH}$
RMgX, then another aldehyde R′CHO	R joins R′CHO	Secondary alcohol	$\mathrm{C_6H_5MgBr + CH_3CHO \to C_6H_5CH(OH)CH_3}$
RMgX, then a ketone	R joins the ketone	Tertiary alcohol	$\mathrm{CH_3MgBr + CH_3COCH_3 \to (CH_3)_3COH}$
Two RMgX on an ester R′COOEt	Two R groups join; OEt leaves	Tertiary alcohol with two identical R groups	$\mathrm{2\,CH_3MgBr + CH_3COOC_2H_5 \to (CH_3)_3COH}$
RMgX, then $\mathrm{CO_2}$ and $\mathrm{H_3O^+}$	+1 on R	Carboxylic acid RCOOH	$\mathrm{CH_3MgBr \to CH_3COOH}$
$\mathrm{NaNH_2}$ on a terminal alkyne, then a primary RX	+ the carbons of R	Longer internal alkyne	$\mathrm{CH_3C{\equiv}CH \to CH_3C{\equiv}CCH_2CH_3}$ with $\mathrm{CH_3CH_2Br}$
Base on $\mathrm{ArCH_2CN}$ , then a ketone	The α-carbon joins the C=O carbon	β-Hydroxy nitrile	$\mathrm{C_6H_5CH_2CN + CH_3COCH_3 \to (CH_3)_2C(OH)CH(C_6H_5)CN}$
Ethylene glycol and $\mathrm{H^+}$ on a C=O	0 (temporary)	Cyclic acetal, stable to base, Grignard reagents and $\mathrm{NaBH_4}$	Aqueous acid gives the C=O back
$\mathrm{X_2/NaOH}$ on a methyl ketone	−1	Carboxylate and $\mathrm{CHX_3}$	$\mathrm{CH_3COCH_2CH_3 \to CH_3CH_2COO^-}$
Soda lime on RCOONa	−1	Alkane RH	$\mathrm{CH_3CH_2COONa \to CH_3CH_3}$
$\mathrm{Br_2/NaOH}$ on an amide $\mathrm{RCONH_2}$	−1	Primary amine $\mathrm{RNH_2}$	$\mathrm{CH_3CH_2CONH_2 \to CH_3CH_2NH_2}$

Mark the steps that change the carbon count before anything else; every other reagent changes only the group.

Common traps

A Grignard reagent attacks an ester twice

After the first addition the ester loses

\mathrm{OEt^-}

and becomes a ketone, which is more reactive than the ester, so a second equivalent adds at once. The product is a tertiary alcohol with two identical groups from the Grignard reagent, never a ketone.

H₂/Ni adds hydrogen, not carbon

Reducing

\mathrm{C{\equiv}N}

to

\mathrm{CH_2NH_2}

keeps the carbon count; the extra carbon came in with the cyanide. Count it once, at the KCN step.

An O–H in the molecule destroys the carbanion

Grignard reagents and acetylide ions are strong bases. A free OH, COOH or NH in the same reaction protonates them before any C–C bond forms, so in practice such groups are protected first.

Acylate, then reduce, for a straight chain

Friedel-Crafts alkylation with a primary halide rearranges and can add more than one group. Acylation gives one straight-chain ketone, and Clemmensen or Wolff-Kishner reduction turns it into the straight-chain alkylbenzene.

Clemmensen leaves COOH alone

Zn–Hg and HCl reduce a ketone or aldehyde C=O to

\mathrm{CH_2}

but do not touch a carboxylic acid. A keto acid becomes an acid with the same number of carbons.

Diazotise cold

The diazonium salt is made with

\mathrm{NaNO_2/HCl}

at 0–5 °C. Warmed in water it turns into the phenol, so a scheme that needs ArI or ArCN keeps it cold until the replacing reagent is added.

Named Reactions

Learn this subtopic in the notes

Named reactions of alkyl halides, aryl halides and diazonium salts

Name	Reagent	Change	Example
Wurtz	Na, dry ether	2 RX → R–R	$\mathrm{2\,CH_3CH_2Br \to CH_3CH_2CH_2CH_3}$
Fittig	Na, dry ether	2 ArX → Ar–Ar	$\mathrm{2\,C_6H_5Br \to C_6H_5{-}C_6H_5}$ (biphenyl)
Wurtz-Fittig	Na, dry ether	ArX + RX → Ar–R	$\mathrm{C_6H_5Br + CH_3CH_2Br \to C_6H_5CH_2CH_3}$
Finkelstein	NaI, dry acetone	R–Cl or R–Br → R–I	$\mathrm{CH_3CH_2Br \to CH_3CH_2I}$
Swarts	AgF, $\mathrm{Hg_2F_2}$ , $\mathrm{CoF_2}$ or $\mathrm{SbF_3}$	R–Cl or R–Br → R–F	$\mathrm{CH_3Br \to CH_3F}$
Sandmeyer	CuCl/HCl, CuBr/HBr or CuCN	$\mathrm{ArN_2^+}$ → ArCl, ArBr or ArCN	$\mathrm{C_6H_5N_2^+Cl^- \to C_6H_5CN}$ with CuCN
Gattermann	Cu powder with HCl or HBr	$\mathrm{ArN_2^+}$ → ArCl or ArBr	$\mathrm{C_6H_5N_2^+Cl^- \to C_6H_5Cl}$ with Cu/HCl
Balz-Schiemann	$\mathrm{HBF_4}$ , then heat	$\mathrm{ArN_2^+}$ → ArF	$\mathrm{C_6H_5N_2^+Cl^- \to C_6H_5F}$
Lucas	Conc. HCl, anhydrous $\mathrm{ZnCl_2}$	ROH → RCl; rate 3° > 2° > 1°	$\mathrm{(CH_3)_2CHOH \to (CH_3)_2CHCl}$ , cloudy in about 5 min
Nitrile from KCN	KCN (ionic)	RX → R–CN	$\mathrm{CH_3CH_2Br \to CH_3CH_2CN}$
Isocyanide from AgCN	AgCN (covalent)	RX → R–NC	$\mathrm{CH_3CH_2Br \to CH_3CH_2NC}$
Carbylamine	$\mathrm{CHCl_3}$ , alcoholic KOH	Primary amine $\mathrm{RNH_2}$ → R–NC	$\mathrm{C_6H_5NH_2 \to C_6H_5NC}$ , a foul smell

Sodium couples, halide salts swap, copper replaces a diazonium group, silver cyanide attacks through nitrogen.

Named reactions of carbonyls, acids, amides and phenols

Name	Reagent	Change	Example
Rosenmund	$\mathrm{H_2}$ , Pd on $\mathrm{BaSO_4}$	RCOCl → RCHO	$\mathrm{CH_3COCl \to CH_3CHO}$
Stephen	$\mathrm{SnCl_2/HCl}$ , then $\mathrm{H_3O^+}$	RCN → RCHO	$\mathrm{CH_3CN \to CH_3CHO}$
Etard	$\mathrm{CrO_2Cl_2}$ in $\mathrm{CS_2}$ , then $\mathrm{H_3O^+}$	$\mathrm{ArCH_3}$ → ArCHO	Toluene → benzaldehyde
Gattermann-Koch	CO, HCl, anhydrous $\mathrm{AlCl_3}$ (CuCl)	ArH → ArCHO	Benzene → benzaldehyde
Clemmensen	Zn–Hg, conc. HCl	C=O → $\mathrm{CH_2}$ , in acid	$\mathrm{CH_3COCH_3 \to CH_3CH_2CH_3}$
Wolff-Kishner	$\mathrm{NH_2NH_2}$ , then KOH in ethylene glycol, heat	C=O → $\mathrm{CH_2}$ , in base	$\mathrm{C_6H_5COCH_2CH_3 \to C_6H_5CH_2CH_2CH_3}$
Cannizzaro	Concentrated NaOH or KOH	2 RCHO (no α-H) → $\mathrm{RCH_2OH + RCOO^-}$	$\mathrm{2\,HCHO \to CH_3OH + HCOO^-}$
Aldol	Dilute NaOH	Two carbonyls with α-H → β-hydroxy carbonyl	$\mathrm{2\,CH_3CHO \to CH_3CH(OH)CH_2CHO}$
Hell-Volhard-Zelinsky (HVZ)	$\mathrm{Cl_2}$ or $\mathrm{Br_2}$ , red P, then $\mathrm{H_2O}$	$\mathrm{RCH_2COOH \to RCHXCOOH}$	$\mathrm{CH_3COOH \to ClCH_2COOH}$
Hofmann bromamide	$\mathrm{Br_2}$ , NaOH	$\mathrm{RCONH_2 \to RNH_2}$ , one carbon fewer	$\mathrm{C_6H_5CONH_2 \to C_6H_5NH_2}$
Reimer-Tiemann	$\mathrm{CHCl_3}$ , aqueous NaOH, then $\mathrm{H_3O^+}$	Phenol → 2-hydroxybenzaldehyde	$\mathrm{C_6H_5OH \to HOC_6H_4CHO}$ (salicylaldehyde)
Kolbe	NaOH, $\mathrm{CO_2}$ at 4–7 atm and 400 K, then $\mathrm{H^+}$	Phenol → 2-hydroxybenzoic acid	$\mathrm{C_6H_5OH \to HOC_6H_4COOH}$ (salicylic acid)
Haloform	$\mathrm{X_2}$ , NaOH	$\mathrm{CH_3COR \to CHX_3 + RCOO^-}$	$\mathrm{CH_3COCH_3 \to CHI_3 + CH_3COO^-}$
Decarboxylation	Soda lime (NaOH and CaO), heat	RCOONa → RH	$\mathrm{CH_3COONa \to CH_4}$

Learn each row as reagent plus change; a match list gives you one and asks for the other.

Mechanism class and reagent roles

Reaction or reagent	Class or role	Key species	Result
Williamson synthesis: RONa + primary RX	Nucleophilic substitution ( $\mathrm{S_N2}$ )	Alkoxide ion	Ether
tert-Butyl bromide in water	Nucleophilic substitution ( $\mathrm{S_N1}$ )	Tertiary carbocation	2-Methylpropan-2-ol
Nitration, sulphonation, Friedel-Crafts	Electrophilic substitution	$\mathrm{NO_2^+}$ , $\mathrm{SO_3}$ , $\mathrm{R^+}$ or $\mathrm{RCO^+}$	Substituted arene
$\mathrm{Br_2}$ on an alkene	Electrophilic addition	Cyclic bromonium ion	Vicinal dibromide
HCN on a ketone	Nucleophilic addition	Cyanide ion	Cyanohydrin
$\mathrm{Cl_2}$ on methane or on toluene's side chain, in light	Free-radical substitution	Cl atom; methyl or benzyl radical	Chloromethane or benzyl chloride
$\mathrm{Cl_2}$ on benzene in UV light, no catalyst	Free-radical addition	Cl atom	Benzene hexachloride, $\mathrm{C_6H_6Cl_6}$
Alcoholic KOH on an alkyl halide	β-Elimination	Strong base in ethanol	Alkene, the more substituted one
Heating a quaternary ammonium hydroxide	Hofmann elimination	Bulky trialkylamine leaving group	The less substituted (anti-Saytzeff) alkene
Lindlar's catalyst with $\mathrm{H_2}$	Partial hydrogenation	Poisoned palladium	Alkyne to cis-alkene
Na in liquid $\mathrm{NH_3}$	Dissolving-metal reduction	Solvated electrons	Alkyne to trans-alkene
Hinsberg reagent, $\mathrm{C_6H_5SO_2Cl}$	Test that sorts amines	Sulphonamide	1° dissolves in alkali, 2° does not, 3° does not react
Na with $\mathrm{H_2}$	Not a reducing system for organic groups	Sodium hydride forms	No organic group is reduced

Name the species that attacks and whether it adds or replaces; the class follows from those two facts.

Common traps

Sandmeyer uses a copper(I) salt, Gattermann uses copper powder

Both replace

\mathrm{N_2^+}

by Cl or Br. CuCl with HCl (or CuBr with HBr) is Sandmeyer; Cu powder with HCl or HBr is Gattermann. A match list that pairs 'Cu, HCl' with Sandmeyer is wrong.

AgCN gives the isocyanide, KCN the nitrile

KCN is ionic, and the free cyanide ion attacks through its carbon. AgCN is largely covalent, so the nitrogen lone pair attacks. The same alkyl halide gives R–CN with KCN and R–NC with AgCN.

Wurtz-Fittig needs one aryl and one alkyl halide

Two aryl halides with sodium is the Fittig reaction and gives a biaryl; two alkyl halides is the Wurtz reaction. Only the mixed pair, ArX with RX, is Wurtz-Fittig and gives an alkylbenzene.

Rosenmund stops at the aldehyde

The palladium is poisoned with

\mathrm{BaSO_4}

so that

\mathrm{H_2}

reduces the acid chloride only as far as the aldehyde. The product is never the carboxylic acid, and with an unpoisoned catalyst it would go on to the alcohol.

Hofmann bromamide loses a carbon

The carbonyl carbon of the amide leaves as carbonate, so benzamide gives aniline and propanamide gives ethanamine. Acid hydrolysis of an amide, by contrast, keeps every carbon and gives the carboxylic acid.

Reimer-Tiemann gives an aldehyde, Kolbe gives an acid

Both work ortho to the OH of phenol. Chloroform and alkali (Reimer-Tiemann) add CHO; carbon dioxide under pressure with sodium phenoxide (Kolbe) adds COOH.

Toluene and chlorine: light or catalyst decides where

In light or on heating, chlorine atoms take a benzylic H and give benzyl chloride: free-radical substitution on the side chain. With

\mathrm{FeCl_3}

in the dark,

\mathrm{Cl^+}

attacks the ring: electrophilic substitution at ortho and para.

Benzene hexachloride is an addition product

Benzene with chlorine in UV light and no catalyst adds three

\mathrm{Cl_2}

molecules to give

\mathrm{C_6H_6Cl_6}

. It is not chlorobenzene and not a substitution.

Alcoholic KOH eliminates, aqueous KOH substitutes

In ethanol, KOH acts as a strong base and removes a β-hydrogen to give an alkene. In water, hydroxide acts as a nucleophile and replaces the halogen to give an alcohol.

Functional Group Identification Tests

Learn this subtopic in the notes

Functional-group tests: reagent, group and observation

Test (reagent)	Detects	Positive result	Example that passes
Bromine water	C=C or C≡C; also phenol and aniline	Reddish-orange colour disappears; white precipitate with phenol or aniline	Cyclohexene
Baeyer's reagent: cold, dilute, alkaline $\mathrm{KMnO_4}$	C=C or C≡C	Pink colour disappears; brown $\mathrm{MnO_2}$	But-2-ene
Ceric ammonium nitrate	Alcoholic –OH	Yellow solution turns red	Ethanol
Neutral $\mathrm{FeCl_3}$	Phenol (and enols)	Violet, blue, green or red colour	Phenol gives violet
Phthalein dye: phthalic anhydride and conc. $\mathrm{H_2SO_4}$ , then NaOH	Phenol	Pink or red dye in alkali	Phenol gives phenolphthalein
Lucas reagent: conc. HCl and $\mathrm{ZnCl_2}$	Class of alcohol	Cloudy at once for 3°, in about 5 min for 2°, not at room temperature for 1°	2-Methylpropan-2-ol, at once
2,4-Dinitrophenylhydrazine (2,4-DNP)	C=O of aldehydes and ketones	Yellow, orange or orange-red precipitate	Propanone
Tollens' reagent: ammoniacal $\mathrm{AgNO_3}$	Aldehyde, aliphatic or aromatic	Silver mirror	Benzaldehyde
Fehling's or Benedict's solution	Aliphatic aldehyde	Red-brown precipitate of $\mathrm{Cu_2O}$	Ethanal
Schiff's reagent	Aldehyde	Pink or magenta colour returns	Methanal
Iodoform: $\mathrm{I_2}$ and NaOH, or KI and NaOCl	$\mathrm{CH_3CO{-}}$ or $\mathrm{CH_3CH(OH){-}}$	Yellow precipitate of $\mathrm{CHI_3}$	Propan-2-ol
$\mathrm{NaHCO_3}$ solution	Carboxylic acid	Brisk effervescence of $\mathrm{CO_2}$	Ethanoic acid
Carbylamine: $\mathrm{CHCl_3}$ and alcoholic KOH	Primary amine, aliphatic or aromatic	Foul-smelling isocyanide	Aniline
Hinsberg's reagent, $\mathrm{C_6H_5SO_2Cl}$	Primary, secondary or tertiary amine	1°: product dissolves in alkali; 2°: insoluble solid; 3°: no reaction	Ethanamine dissolves; N-methylaniline gives an insoluble solid
Azo dye: $\mathrm{NaNO_2/HCl}$ at 0–5 °C, then alkaline 2-naphthol	Aromatic primary amine	Orange-red dye	Aniline
Molisch's test: α-naphthol and conc. $\mathrm{H_2SO_4}$	Carbohydrate	Violet ring where the layers meet	Glucose
Biuret test: alkaline $\mathrm{CuSO_4}$	Peptide bond	Violet colour	Egg albumin
Alcoholic $\mathrm{AgNO_3}$ , warm	Reactive C–X: benzylic, allylic or tertiary	AgCl white, AgBr pale yellow precipitate	Benzyl chloride A halogen on the ring (chlorobenzene) gives no precipitate.

Every row is reagent, group and observation; a question gives one and asks for another.

Common traps

Fehling's and Benedict's miss aromatic aldehydes

Benzaldehyde gives a silver mirror with Tollens' reagent but does not reduce Fehling's or Benedict's solution. Only aliphatic aldehydes give the red-brown

\mathrm{Cu_2O}

.

Iodoform needs CH₃CO or CH₃CH(OH)

A tertiary alcohol with a methyl group, such as 2-methylpropan-2-ol, fails: its carbinol carbon has no H, so it cannot be oxidised to a methyl ketone. Ethanol and ethanal pass; methanol, propan-1-ol and propanal fail.

Phenols dissolve in NaOH but not in NaHCO₃

A simple phenol is too weak an acid to release

\mathrm{CO_2}

from hydrogencarbonate. Only carboxylic acids (and strongly acidic phenols such as 2,4,6-trinitrophenol) dissolve in

\mathrm{NaHCO_3}

.

CAN is for alcohols, FeCl₃ is for phenols

Ceric ammonium nitrate gives a red colour with an alcoholic OH; neutral

\mathrm{FeCl_3}

gives a violet or similar colour with a phenol. A match list that swaps them is wrong.

Decolourised bromine water does not prove a C=C

Phenol and aniline also remove the colour of bromine water, by ring substitution, and give a white precipitate. Baeyer's reagent is the cleaner test for a C=C.

Organic Reaction Mechanisms formulas

Carbocations, Rearrangements and Addition Regiochemistry

Carbocation stability and 1,2-shifts

Addition regiochemistry by reagent

Common traps

Carbonyl Reactions: Enolates, Haloform and Cannizzaro

Aldol, Claisen-Schmidt, Claisen and Michael reactions

Haloform, Cannizzaro and decarboxylation

Common traps

Multistep Conversions and Road Maps

Aromatic road maps: acylation, reduction and diazonium routes

Carbon counting in chain-building steps

Common traps

Named Reactions

Named reactions of alkyl halides, aryl halides and diazonium salts

Named reactions of carbonyls, acids, amides and phenols

Mechanism class and reagent roles

Common traps

Functional Group Identification Tests

Functional-group tests: reagent, group and observation

Common traps

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