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11th : Hydrocarbons > Alkanes > Flashcards

Alkanes Flashcards

1
Q

Why are paraffins called so?

A

They have low affinity and don’t react much.

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2
Q

Catalysts for catalytic hydrogenation? Why only d block elements?

A

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

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

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

A

R- gets the cation and Mg(anion)X

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6
Q

General Reaction of Grignard reagent Reagent?

A

R-MgX + reagent —> RH + Mg(Anion)X

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7
Q

General Reaction of Wurtz?

A

(dry ether)

2 R-X + Na ———> R-R + 2NaX

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8
Q

Mechanism of Wurtz?

A

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

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9
Q

Why multiple alkanes aren’t used in Wurtz?

A

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

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10
Q

R-X + Zn + HCl —-> ?

A

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

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11
Q

R-X + ZnCu + C2H5OH —-> ?

A

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

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12
Q

R-X + NaOH + Zn —> ?

A

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

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13
Q

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

A

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

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14
Q

alkanes –> alcohols –> aldehydes —> carboxylic acids

A
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15
Q

General Reaction of Decarboxylation. Why soda lime?

Mechanism?

A

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

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

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16
Q

General Reaction of Kolbe’s Electrolysis?

A

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

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17
Q

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

A

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

18
Q

2 ways of preparing methane are?

A

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

19
Q

Properties of halogenation of alkanes? 4 points

A

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

20
Q

selectivity - favoring certain product more

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

A

Br - 1600:82:1

Cl - 5:3.8:1

21
Q

Flourination is called? Reagent used?

A

Swarts Reaction. AgF

22
Q

Iodination GR? why hno3?

A

alkane + I2 —HIO3, HNO3—-> R-I + HI

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

23
Q

GR of catalytic hydrogenolysis?

A

R-X + h2 —Pd-C—-> R + HX

24
Q

Red phosphorus GR?

A

R-I + HI —-red P—-> R-H + I2

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

25
Q

conditions of nitration of alkanes?

A

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

26
Q

GR of nitration of alkanes? Why less products?

A

R-H + HO-NO2 —> R-NO2 + H20 623K

exothermic reaction which breaks C-C bonds

27
Q

Sulphonation of alkanes reagent and GR? Limitations?

A

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

28
Q

GR of complete oxidation of alkanes?

A

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

29
Q

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

A

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

tertiary hydrogen - kmno4, k2cr2o7 - alcohol

30
Q

reaction with steam? what’s it called?

A

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

31
Q

Reaction conditions for isomerization of alkanes?

A

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

32
Q

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

A

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

33
Q

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

A 
same molecular, structural only different spatial arrangement. 
Rotation of sigma bond
staggered - lies in between
eclipsed - lies parallel
gauche/ skew - anything in between
34
Q

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

A

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

35
Q

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

A

staggered - most stable although they are interconvertible

36
Q

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

A

staggered
anti- conformation
gauche
gauche

37
Q

conditions for geometrical isomers? 2 nomenclatures?

A

c-c double bond
carbon cant have same substituents

trans cis and E - Z

38
Q

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

A

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

39
Q

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

A

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

40
Q

CIS, TRANS - which has a higher solubility why?

A

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

41
Q

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

A

cis - unsymmetrical, unequal electron distribution, polar

trans - it cancels out

11th : Hydrocarbons (4 decks)

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