Alkanes Flashcards
Why are paraffins called so?
They have low affinity and don’t react much.
Catalysts for catalytic hydrogenation? Why only d block elements?
Ni, Pt, Pd - multiple oxidation states + pulverized (area)
Two kinds of nickels - and their conditions. Sabatier Senderen’s Reaction?
Ordinary (drastic conditions ) + raney (alloy of Al) (normal conditions)
Ethene to ethane w raney nickel
What is grignard reagent? How is it formed? Why dry ether?
Alkyl magnesium halids. R-Mg+X-. Aprotic solvent, else mg reacts and liberates h2.
Grignard Reagent + h20/ R-OH / NH3 / RCOOH / R-NH2 —–> ?
R- gets the cation and Mg(anion)X
General Reaction of Grignard reagent Reagent?
R-MgX + reagent —> RH + Mg(Anion)X
General Reaction of Wurtz?
(dry ether)
2 R-X + Na ———> R-R + 2NaX
Mechanism of Wurtz?
RX homolitically break and forms NaX whereas R free radical combines to form R-R
Why multiple alkanes aren’t used in Wurtz?
Mixture of products, may have different BP - but difficult to separate through fractional distillation.
R-X + Zn + HCl —-> ?
R-X + Zn + HCl —-> R-H + Zn2+ + X- + anion of acid (Cl-)
R-X + ZnCu + C2H5OH —-> ?
R-X + ZnCu + C2H5OH —-> R-H + Zn2+ + X- + anion of acid (C2H5O-)
R-X + NaOH + Zn —> ?
R-X + NaOH + Zn —> R-H + H-X + Na2ZnO2
Name the two reducing agents to reduce alkyl halides. How do they react with 1,2,3 degree alkanes + general reaction
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
alkanes –> alcohols –> aldehydes —> carboxylic acids
General Reaction of Decarboxylation. Why soda lime?
Mechanism?
R-COOH + NaOH + CaO —>R-H + Na2CO3 + NaOH
Naoh absorbs water and becomes corrosive. Soda lime has less tendency to absorb water
General Reaction of Kolbe’s Electrolysis?
R-COONa + H2O —-EC—–> R-R + H2 + CO2 + Na2CO3
In alkanes which reaction doubles the carbons, doubles the alkyl part, and reduces carbon atoms by 1 ?
Wurtz Reaction. Kolbe’s method. Decarboxylation reduces one by replacing COOH by H
2 ways of preparing methane are?
ABC — Al4C3/ BeC + H20 —> CH4 + hydroxide
Properties of halogenation of alkanes? 4 points
free radical mechanism. light. heat 520-670K. F>Cl>Br>I
selectivity - favoring certain product more
selectivity ratio - percentage ratio of 1,2,3 degree hydrogens being replaced. For bromine and chlorine?
Br - 1600:82:1
Cl - 5:3.8:1
Flourination is called? Reagent used?
Swarts Reaction. AgF
Iodination GR? why hno3?
alkane + I2 —HIO3, HNO3—-> R-I + HI
hno3 prevents BR. Oxidizes HI to I, NO2, H20
GR of catalytic hydrogenolysis?
R-X + h2 —Pd-C—-> R + HX
Red phosphorus GR?
R-I + HI —-red P—-> R-H + I2
red phosphorous used to prevent BR. P + I2 —>PI3
conditions of nitration of alkanes?
fuming nitric acid + 623K (to make it react)
GR of nitration of alkanes? Why less products?
R-H + HO-NO2 —> R-NO2 + H20 623K
exothermic reaction which breaks C-C bonds
Sulphonation of alkanes reagent and GR? Limitations?
fuming sulphuric acid (h2so4 + so3 + h20)
R-H + H2SO4 —> R- SO3H + H20
ONLY FOR >5 ALKANES OR TERTIARY HYDROGENS
GR of complete oxidation of alkanes?
CnH2n+2 + (3n+1/2) O2 —–> nCO2 + (n+1)H2O
catalytic oxidation of alkanes to form alcohols, aldehydes and carboxylic acids? - reaction conditions? besides o2?
al(cu)hol - cu tube, 573K, 100atm
(mo)ldehyde - Mo2O3, HT, HP
c(ag)boxylic acid - Ag2O, heat
tertiary hydrogen - kmno4, k2cr2o7 - alcohol
reaction with steam? what’s it called?
ch4 + h20 —-1273K Ni—–> co + h20 (water gas)
Reaction conditions for isomerization of alkanes?
n (an) alkanes —> branched alkanes
anhydrous AlCl3 , HCl, 573K and 35atm
only 1 methyl group shifts
Reaction conditions for aromatization? What numbered carbons? What ring? Why? what processes?
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
Conformational isomers - what are they? facilitated by what? 3 forms?
same molecular, structural only different spatial arrangement. Rotation of sigma bond staggered - lies in between eclipsed - lies parallel gauche/ skew - anything in between
Which conformation is more stable and why? What is torsional strain and angle?
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
which state is ethane found in? why, although energy barrier is only 12.55kJ/mol?
staggered - most stable although they are interconvertible
Most stable form of ethane, butane, ethylene glycol and 2fluroethanol?
staggered
anti- conformation
gauche
gauche
conditions for geometrical isomers? 2 nomenclatures?
c-c double bond
carbon cant have same substituents
trans cis and E - Z
CIS, TRANS - which has a higher melting point why?
trans - symmetrical and will have stable crystal lattice hence needs more energy, higher MP
CIS, TRANS - which has a higher boiling point why?
cis - unequal electron distribution, polar and has some attraction, more energy to break it
CIS, TRANS - which has a higher solubility why?
cis - as trans has a more stable lattice, has to break more interactions hence needs more energy and is less soluble
CIS, TRANS - which has a higher dipole moment why?
cis - unsymmetrical, unequal electron distribution, polar
trans - it cancels out
