4.3.7
Ek carbonyl group C=O polarized hota hai: oxygen electrons ka lalchi hota hai, isliye carbon δ + δ −
KYA carbonyls ko react karata hai: π KYU unhe nucleophiles pasand aate hain: ek nucleophile C δ + π O nucleophilic addition hai.KYU α enolate ke roop mein stabilize hota hai). Yeh akela fact aldol, Claisen-Schmidt, Mannich, Perkin, Reformatsky, Knoevenagel — inhe sabko power karta hai.
Alcohols ka oxidation : 1° alcohol → PCC , aldehyde par rokne ke liye); 2° alcohol → Ozonolysis of alkenes: R-CH=CH-R ′ O 3 , Z n / H 2 O Alkynes ka hydration : HC≡CH + H 2 O H g S O 4 , H 2 S O 4 Rosenmund reduction : acid chloride H 2 , P d / B a S O 4 Nitriles/esters se : DIBAL-H dono ko aldehydes tak reduce karta hai (ek hydride delivery, imine/hemiacetal par ruk jaata hai).Friedel–Crafts acylation : arene + RCOCl / A l C l 3 → Gattermann–Koch : arene + C O + H C l / A l C l 3 → aldehyde .
Common mistake "PCC aur KMnO₄ ek hi kaam karte hain"Yeh kyun sahi lagta hai: dono alcohols ko oxidize karte hain. Fix: strong aqueous oxidants (K M n O 4 K 2 C r 2 O 7 / H 2 O poora carboxylic acids tak push karte hain kyunki aldehyde ek hydrate banata hai jo re-oxidize ho jaata hai. PCC (anhydrous) aldehyde par ruk jaata hai kyunki paani nahi = hydrate nahi.
Intuition KYU carbonyls add karte hain, alkenes nahiEk alkene C=C mein do carbons hote hain similar electronegativity ke saath — symmetric, non-polar, isliye nucleophiles use ignore karte hain (electrons electrophiles par attack karte hain, na ki doosre electron clouds par). C=O polarized hai: ek end genuinely electron-poor hai. Toh Nu⁻ ke paas ek target hai.
Worked example Addition products jo aapko yaad hone chahiye
HCN → cyanohydrin R 2 C(OH)CN Kyun? CN⁻ add hota hai, phir O⁻ H⁺ pakad leta hai.
RMgX → Kyun? R–MgX ka C carbanion-jaisa hota hai (Nu).
alcohol (2 eq, H⁺) → acetal R 2 C(OR’) 2 Yeh step kyun? Pehle hemiacetal banta hai; acid OH ko protonate karta hai, paani oxocarbenium ke roop mein nikalti hai, doosra ROH add hota hai.
1° amine → imine (Schiff base) R 2 C=NR’ → enamine . Kyun? Addition ke baad paani nikalta hai; geometry imine vs enamine decide karti hai.
Intuition Unifying engineBase (ya acid) ek acidic α-H nikaalta hai ⇒ enolate (nucleophilic carbon). Yeh carbanion ek electrophile par attack karta hai. Electrophile kya hai yeh naam decide karta hai:
Electrophile
Reaction
doosra carbonyl
Aldol / Claisen-Schmidt
iminium ion (amine + HCHO se)
Mannich
aldehyde, anhydride ke saath
Perkin
aldehyde, Zn–ester ke saath (base nahi!)
Reformatsky
Worked example Benzaldehyde + acetophenone→ PhCH=CH-COPh Yeh step kyun? Benzaldehyde mein koi α-H nahi , isliye woh enolate nahi bana sakta — woh sirf electrophile ho sakta hai. Acetophenone enolate supply karta hai. Isse ek messy mixture se bacha jaata hai.
BrCH 2 COOEt + Z n → → β-hydroxy ester .
Zn kyun, strong base kyun nahi? Zinc enolate mild hai — aldehydes par attack karta hai lekin ester ko self-condense nahi karta. Controlled C–C bonds milte hain.
( CH 3 CO ) 2 O CH 3 COO − Na + Δ cinnamic acid ArCH=CHCOOH.
Anhydride kyun? Acetate base anhydride ka α-H deprotonate karta hai; enolate ArCHO ke saath aldol-type addition karta hai, phir dehydration + hydrolysis hoti hai.
Intuition YEH KYU HOTA HAIAldehydes jisme α-H nahi hota (HCHO, PhCHO) enolates nahi bana sakte, isliye aldol ki jagah woh disproportionation karte hain: ek molecule acid mein oxidize hota hai, doosra alcohol mein reduce hota hai.
2 PhCHO conc. NaOH PhCOO − + PhCH 2 OH Mechanism: OH⁻ ek PhCHO mein add hota hai → hydride transfer karta hai doosre PhCHO ko. Hydride donor carboxylate ban jaata hai; acceptor alcohol ban jaata hai.
Crossed Cannizzaro: excess HCHO ke saath, HCHO hamesha oxidize hota hai (best hydride donor), doosra aldehyde hamesha reduce hota hai.
Recall Jab α-H nahi, reagent se choose karo
conc. NaOH ⇒ Cannizzaro
CN⁻ ⇒ Benzoin
aldehyde with α-H + base ⇒ Claisen–Schmidt
Ketones se aldehydes nucleophiles ke liye zyada reactive kyun hote hain? Aldehydes mein ek R hota hai (kam +I, kam steric); C par zyada δ +
Kaun sa reagent 1° alcohol ko aldehyde tak oxidize karta hai (wahin rukta hai) aur kyun? PCC; anhydrous hai, isliye koi hydrate nahi banta jo acid tak re-oxidize ho sake.
Nucleophilic addition ka rate-determining feature kya hai? Nu⁻ ka electrophilic carbonyl carbon par attack, electrons O par jaate hain alkoxide banate hue.
Benzaldehyde Cannizzaro kyun karta hai, aldol nahi? Isme koi α-H nahi, isliye enolate nahi ban sakta; disproportionation hoti hai.
Crossed Cannizzaro mein HCHO ke saath kaun sa aldehyde oxidize hota hai? HCHO (best hydride donor) formate mein oxidize hota hai; doosra alcohol mein reduce hota hai.
Wittig reaction ko aage kyun drive karta hai? Bahut stable P h 3 P = O
Reformatsky mein strong base ki jagah Zn kyun use karte hain? Zinc enolate mild hai — aldehyde mein add hota hai ester ko self-condense kiye bina.
Mannich mein enol kaun se electrophile par attack karta hai? Ek iminium ion [ C H 2 = N R 2 ] +
Benzoin condensation mein umpolung kya hai? CN⁻ carbonyl carbon ko nucleophilic banata hai (polarity reversal), toh ek aldehyde C doosre par attack karta hai.
Perkin reaction ke reagents kya hain? Aromatic aldehyde + acid anhydride + acid ka sodium salt, heat → cinnamic acid.
Rosenmund reduction kya ko kya mein convert karta hai? Acid chloride → aldehyde (H₂, Pd/BaSO₄ poisoned catalyst).
Aldol ka dehydration ke baad product kya hota hai? α,β-unsaturated carbonyl (conjugated, zyada stable).
Recall Feynman: 12 saal ke bache ko samjhaoCarbonyl carbon ek aaise bache ki tarah hai jo "+" sign pakde hua hai — use electrons chahiye. Jiske paas extra electrons hain (nucleophile) woh daudta hua aata hai aur use pakad leta hai; oxygen extra electrons pakad leta hai. Ab, agar carbon ke paas ek neighbour H hai jo thoda loose hai, toh ek base us H ko kheench sakta hai aur us molecule ko electron-rich attacker mein badal deta hai — toh do carbonyl molecules ek saath chipak sakte hain (yahi aldol aur friends hain). Agar koi loose H nahi hai (jaise benzaldehyde), toh woh us tarah chipak nahi sakte, isliye ek molecule doosre par ek H dhakka deta hai: ek acid ban jaata hai, ek alcohol (Cannizzaro). Wittig bas ek special partner (ylide) hai jo O ki jagah ek double bond swap kar deta hai.
Mnemonic α-H families yaad karne ke liye"All Cool Magicians Really Perform Wittig & Benzoin Cleverly"
A ldol, C laisen-Schmidt, M annich, R eformatsky, P erkin = α-H/enolate chahiye. W ittig, B enzoin, C annizzaro = no-α-H / special trio.
Mnemonic No-α-H decision:"NaOH→Cannot(zzaro), CN→Benzoin"
Alcohols — oxidation and PCC Grignard reagents and organometallics Enols and enolates — keto-enol tautomerism Friedel–Crafts acylation Carboxylic acids and derivatives Reduction reagents — DIBAL, LiAlH4, NaBH4
Aldol Claisen-Schmidt Mannich
