Alkanes

Question 1

Why are paraffins called so?

Answer 1

They have low affinity and don’t react much.

Question 2

Catalysts for catalytic hydrogenation? Why only d block elements?

Answer 2

Ni, Pt, Pd - multiple oxidation states + pulverized (area)

Question 3

Two kinds of nickels - and their conditions. Sabatier Senderen’s Reaction?

Answer 3

Ordinary (drastic conditions ) + raney (alloy of Al) (normal conditions)
Ethene to ethane w raney nickel

Question 4

What is grignard reagent? How is it formed? Why dry ether?

Answer 4

Alkyl magnesium halids. R-Mg+X-. Aprotic solvent, else mg reacts and liberates h2.

Question 5

Grignard Reagent + h20/ R-OH / NH3 / RCOOH / R-NH2 —–> ?

Answer 5

R- gets the cation and Mg(anion)X

Question 6

General Reaction of Grignard reagent Reagent?

Answer 6

R-MgX + reagent —> RH + Mg(Anion)X

Question 7

General Reaction of Wurtz?

Answer 7

(dry ether)

2 R-X + Na ———> R-R + 2NaX

Question 8

Mechanism of Wurtz?

Answer 8

RX homolitically break and forms NaX whereas R free radical combines to form R-R

Question 9

Why multiple alkanes aren’t used in Wurtz?

Answer 9

Mixture of products, may have different BP - but difficult to separate through fractional distillation.

Question 10

R-X + Zn + HCl —-> ?

Answer 10

R-X + Zn + HCl —-> R-H + Zn2+ + X- + anion of acid (Cl-)

Question 11

R-X + ZnCu + C2H5OH —-> ?

Answer 11

R-X + ZnCu + C2H5OH —-> R-H + Zn2+ + X- + anion of acid (C2H5O-)

Question 12

R-X + NaOH + Zn —> ?

Answer 12

R-X + NaOH + Zn —> R-H + H-X + Na2ZnO2

Question 13

Name the two reducing agents to reduce alkyl halides. How do they react with 1,2,3 degree alkanes + general reaction

Answer 13

LiAlH4 (1,2 - alkane 3- alkene) and NaBH4 (all alkane).
1,2 R-X + LiAlH4 —> R-H + LiX + AlH3
3 R-X + LiAlH4 —> alkene + LiX + AlH3

Question 14

alkanes –> alcohols –> aldehydes —> carboxylic acids

Question 15

General Reaction of Decarboxylation. Why soda lime?

Mechanism?

Answer 15

R-COOH + NaOH + CaO —>R-H + Na2CO3 + NaOH

Naoh absorbs water and becomes corrosive. Soda lime has less tendency to absorb water

Question 16

General Reaction of Kolbe’s Electrolysis?

Answer 16

R-COONa + H2O —-EC—–> R-R + H2 + CO2 + Na2CO3

Question 17

In alkanes which reaction doubles the carbons, doubles the alkyl part, and reduces carbon atoms by 1 ?

Answer 17

Wurtz Reaction. Kolbe’s method. Decarboxylation reduces one by replacing COOH by H

Question 18

2 ways of preparing methane are?

Answer 18

ABC — Al4C3/ BeC + H20 —> CH4 + hydroxide

Question 19

Properties of halogenation of alkanes? 4 points

Answer 19

free radical mechanism. light. heat 520-670K. F>Cl>Br>I

Question 20

selectivity - favoring certain product more

selectivity ratio - percentage ratio of 1,2,3 degree hydrogens being replaced. For bromine and chlorine?

Answer 20

Br - 1600:82:1

Cl - 5:3.8:1

Question 21

Flourination is called? Reagent used?

Answer 21

Swarts Reaction. AgF

Question 22

Iodination GR? why hno3?

Answer 22

alkane + I2 —HIO3, HNO3—-> R-I + HI

hno3 prevents BR. Oxidizes HI to I, NO2, H20

Question 23

GR of catalytic hydrogenolysis?

Answer 23

R-X + h2 —Pd-C—-> R + HX

Question 24

Red phosphorus GR?

Answer 24

R-I + HI —-red P—-> R-H + I2

red phosphorous used to prevent BR. P + I2 —>PI3

Question 25

conditions of nitration of alkanes?

Answer 25

fuming nitric acid + 623K (to make it react)

Question 26

GR of nitration of alkanes? Why less products?

Answer 26

R-H + HO-NO2 ---> R-NO2 + H20 623K | exothermic reaction which breaks C-C bonds

Question 27

Sulphonation of alkanes reagent and GR? Limitations?

Answer 27

fuming sulphuric acid (h2so4 + so3 + h20) R-H + H2SO4 ---> R- SO3H + H20 ONLY FOR >5 ALKANES OR TERTIARY HYDROGENS

Question 28

GR of complete oxidation of alkanes?

Answer 28

CnH2n+2 + (3n+1/2) O2 -----> nCO2 + (n+1)H2O

Question 29

catalytic oxidation of alkanes to form alcohols, aldehydes and carboxylic acids? - reaction conditions? besides o2?

Answer 29

al(cu)hol - cu tube, 573K, 100atm (mo)ldehyde - Mo2O3, HT, HP c(ag)boxylic acid - Ag2O, heat tertiary hydrogen - kmno4, k2cr2o7 - alcohol

Question 30

reaction with steam? what's it called?

Answer 30

ch4 + h20 ----1273K Ni-----> co + h20 (water gas)

Question 31

Reaction conditions for isomerization of alkanes?

Answer 31

n (an) alkanes ---> branched alkanes anhydrous AlCl3 , HCl, 573K and 35atm only 1 methyl group shifts

Question 32

Reaction conditions for aromatization? What numbered carbons? What ring? Why? what processes?

Answer 32

MVC A - catalysts like mo2o3, v2o5, cr2o3 supported over al2o3 at 773K 10-20atm 6-8C benzene ring 7,8 rings aren't aromatic by Huckel's rule cyclization, isomerization and dehydrogenation

Question 33

Conformational isomers - what are they? facilitated by what? 3 forms?

Answer 33

``` same molecular, structural only different spatial arrangement. Rotation of sigma bond staggered - lies in between eclipsed - lies parallel gauche/ skew - anything in between ```

Question 34

Which conformation is more stable and why? What is torsional strain and angle?

Answer 34

Staggered - more distance less repulsion the repulsion interaction of electron clouds which affects stability of conformations angle of c-c bond that decides magnitude of strain

Question 35

which state is ethane found in? why, although energy barrier is only 12.55kJ/mol?

Answer 35

staggered - most stable although they are interconvertible

Question 36

Most stable form of ethane, butane, ethylene glycol and 2fluroethanol?

Answer 36

staggered anti- conformation gauche gauche

Question 37

conditions for geometrical isomers? 2 nomenclatures?

Answer 37

c-c double bond carbon cant have same substituents trans cis and E - Z

Question 38

CIS, TRANS - which has a higher melting point why?

Answer 38

trans - symmetrical and will have stable crystal lattice hence needs more energy, higher MP

Question 39

CIS, TRANS - which has a higher boiling point why?

Answer 39

cis - unequal electron distribution, polar and has some attraction, more energy to break it

Question 40

CIS, TRANS - which has a higher solubility why?

Answer 40

cis - as trans has a more stable lattice, has to break more interactions hence needs more energy and is less soluble

Question 41

CIS, TRANS - which has a higher dipole moment why?

Answer 41

cis - unsymmetrical, unequal electron distribution, polar | trans - it cancels out