Alkenes

Question 1

Stereospecific catalysts added in presence of H2 for partial reduction of alkynes?

Answer 1

`Lindlar’s catalyst - Pd/ CaCO3 or BaSO4, poisoned by S - cis
Birch Reduction - Na in liq NH3 - trans

Question 2

in the formation of alkenes by alkyl halides which is the most reactive?

Answer 2

R-I > R-Br > R-Cl

Question 3

Alkenes from monodydric alcohols? Reagent?

Answer 3

Dehydration. Conc. H2SO4 + heat

Question 4

GR of Kolbe’s Electrolytic method of preparation of alkenes?

Answer 4

R-COONa/K
|
R-COONa/K + H20 —EC—> R=R + CO2 + H2 + CARBONATE + HYDROXIDE

Question 5

GR of vic or gem dihalide to form alkenes?

Answer 5

react it with zn dust in presence of ch3oh and heat it

R-X2 + Zn ——> alkene + ZnX2

Question 6

gem dihalide + Na in dry ether leads to what? why is this process not used? For what is this helpful?

Answer 6

Wurtz reaction occurs in two steps eventually to form an alkene.
Not done as alkene –> alkyl dihalide —> alkene = STOOPID
Purification of alkenes

Question 7

Why do alkenes undergo electrophilic addition reactions?

Answer 7

1. double bond which acts as a nucleophile

2. pi bond breaks to form 2 sigma bonds. energy given out = more stability

Question 8

Test for unsaturation of alkenes?

Answer 8

Addition of Br2 in CCl4 which is reddish brown. If color disappears indicates it was previously unsaturated.

Question 9

Addition of halogens to alkenes , F and I why are they not preferred?

Reagent?

Answer 9

F - explosive
I - usually reversible, drastic conditions

CCl4

Question 10

Order or reactivity of hydrogen halides?

Answer 10

H-I > H-Br > H-Cl

low bond dissociation enthalpy

Question 11

Peroxide effect not seen in others except HBr, why?

Answer 11

HF - initiation of F free radical not seen

HCl, HBr - involve endothermic steps, not stable (during propagation )

Question 12

How are hypohalous acids formed? How do they ionize?

Answer 12

X + H20 —> HOX + HX

HOX —> X+ + OH-

Question 13

Reaction conditions of addition of sulfuric acid to alkenes? How does the product form? What happens when u add water? Reaction conditions for that?

Answer 13

cold conc H2SO4
H+ OSO3H- (according to markovnikov’s rule)
OSO3H gets replaced by OH and u get alcohol and H2SO4
heat and H+

Question 14

Controlled Oxidation of Alkenes : Epoxides?

Answer 14

conditions - o2 , Ag, 575K

only one bond breaks and a triangle of C-C-O forms

Question 15

Controlled Oxidation of Alkenes : Alcohols? By products?

Name of reaction?

Answer 15

Vicinal diols.
cold, dil KMnO4 (298K - 303K)
only one bond breaks and OH is added. Hydrogen number remains same to that OH is added
KMnO4 + H2O ---> KOH + MnO2 + [O]
HYDROXYLATION

Question 16

Controlled Oxidation of Alkenes : Carboxylic Acids and Ketones?
What happens if methanoic acid is formed?

Answer 16

K(arboxylic)
hot KMnO4 (373-383K)
both bonds break, double bond O is added and O before H if any
it gets oxidized to CO2 and H2O

Question 17

Controlled Oxidation of Alkenes : Aldehydes and Ketones?

Name?

Answer 17

(o)ldehydes
OZONOLYSIS.
add O3 —> both bonds break, addition of 3O in the form of Pentagon (ozonide)
Then Zn/H20 —-> ZnO + add double bond O

Question 18

Reaction conditions for polymerization?

Answer 18

high temp, high pressure, catalyst, peroxide to stop the reaction