Alkenes

Question 1

Compare MP BP of cis- and trans- isomers

Answer 1

Trans higher MP, able to pack more efficiently in a lattice structure, higher intermolecular forces per unit volume, req more energy to break.

Cis (polar) higher BP due to pd-pd vs id-id.

Question 2

Two ways to obtain alkenes (lab) + two (industrial)

Answer 2

1. Alcohols via Elim of water
2. Halogeno via Elim of HX
3. Catalytic cracking with zeolite catalyst
4. Thermal cracking via High temp and pressure

Question 3

Alcohol -> Alkene

Answer 3

HEAT w
Excess Conc. H2SO4
OR
Pass over Al2O3 (s)

Question 4

Halogenoalkane -> Alkene

Answer 4

HEAT w Ethanolic KOH

Apply Zaitsev

Question 5

Rxn of Alkenes (5)

Answer 5

1. Combustion
2. E Add
3. Hydration
4. Reduction
5. Oxidation

Question 6

E Addition Mech (2 steps)

Answer 6

1: e rich C=C reacts with ephile to give carbocation
2: carbocation reacts with e rich species

Question 7

Alkene -> Alkane w Br Br

Answer 7

ROOM TEMP w Br2 in CCl4

Question 8

Alkene -> Alkane w Br OH

Answer 8

ROOM TEMP w Br2 (aq)

Question 9

Alkene -> Alkane w H Br

Answer 9

ROOM TEMP w HBr (g)

Question 10

Alkene -> Alkane with H OH

Answer 10

ROOM TEMP Conc. H2SO4 +

Water + WARM

Question 11

Alkene -> Alkane

Answer 11

H2, Pt catalyst

Question 12

Alkenes -> Alkane w OH OH

Answer 12

Mild Oxi

KMnO4, NaOH (aq), COLD

Question 13

Alkenes -> C. Acid (+ CO2 + H2O)

Answer 13

Vigorous Oxi

KMnO4, H2SO4 (aq), HEAT

Question 14

Can alkenes oxi with K2Cr2O7?

Answer 14

No, too weak

Question 15

Can alkene be reduced by H2, Pt?

Answer 15

Yes but not by LiAlH4