Chemistry class 12 most important notes from upcoming exams
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Course
Chemistry
Institution
Sixth Year / 12th Grade
From alkene
2. From carbonyl compound
3. From Grignard’s reagent
4. From 1° amine
5. From hydrolysis of ester
6. From alkyl halide
1. From alkene:
i. Acid catalysed hydration
ii. Hydroboration oxidation
iii. Oxo process
i. Acid catalysed hydration:
CH3 CH CH2
+ H2O
H
+
H2
S
O4
...
Alcohol Reactions
Preparation of alcohols:
1. From alkene
2. From carbonyl compound
3. From Grignard’s reagent
4. From 1° amine
5. From hydrolysis of ester
6. From alkyl halide
1. From alkene:
i. Acid catalysed hydration
ii. Hydroboration oxidation
iii. Oxo process
According to Markonikov’s rule, in case of unsymmetrical alkenes, 𝐻 + goes to that
carbon of double bond which has more hydrogen or 𝑂𝐻 − goes to carbon having least
hydrogen.
Mechanism:
+ +
step-1 CH3 CH CH2 + H3O CH3 C CH3 + H2O (slow)
electrophile H
+
H2O
+
step-2 CH3 C CH3 + H2O CH3 CH CH3 (H2O acts as a neucleophile)
H
+
H2O
OH
+ +
step-3 CH3 CH CH3 H CH3 CH CH3 ( H is taken by HSO4 )
Q. Compare rate of hydration.
CH3 C CH2 > CH3 CH CH2 > CH2 CH2 (3°>2°>1°)
CH3
Because carbon is formed during the mechanism.
Q.
CH3 CH3
H2SO4
CH3 CH CH CH2 CH3 C CH2 CH3 (due to hydride shift)
H 2O
OH
ii. Hydroboration oxidation: (It follows anti-markonikov’s rule)
Here diborane 𝐵2 𝐻6 or (𝐵𝐻3 )2 reacts with alkene.
O OH
Pd, Pt, Ni or
CH3 C H + H2
NaBH4 or LiAlH4
CH3 CH2 ( 1°)
O OH
Pd, Pt, Ni or
CH3 C CH3 + H2
NaBH4 or LiAlH4
CH3 C CH3 ( 2°)
H
O OH
Trick:-Reduction means addition of hydrogen.CH3 C H +H H CH3 CH2
→ Reduction in presence of H2/Pd, Pt, Ni is called catalytic reduction or catalytic
hydrogenation.
→ H2/Pd, Pt, Ni can reduce double bond. LiAlH4 reduce only in a special case. NaBH4 never
reduce double bond.
C C C C CHO + 2H2 PdLiAlH
/ Pt / Ni
4
C C C C C OH
But LiALH4 can reduce double bond only in case of 𝛼 − 𝛽 unsaturated double bond
(Not in ketone)
LiAlH4
C C C C CHO C C C C C OH
→ LiAlH4 is more effective than NaBH4 as size of Al is larger than B.
So easier to remove hydrogen from Al. NaBH4 can reduce aldehyde and ketone. It can not
reduce acid derivatives. But LiAlH4 can.
O O
ii. Reduction of R-COOH, R C O R', R C Cl
LiAlH4 in ether or
R COOH R CH2 OH
B2 H 6
B2H6 does not reduce ester, Nitro, halo. But Here B2H6 is better than LiAlH4.
LiAlH4 is very expensive. So commercially, acid is converted to easter then to
alcohol.
2
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