Catalytic Hydrogenation of Alkenes

Catalyst with Hydrogen adsorbed

Catalyst with Hydrogen and alkene adsorbed

Hydrogen inserted into C = C

Alkane product released from catalyst

Heterogeneous catalyst Pt. Pd. Ni-tinely divided metal SYN addition of hydrogen

Alkene + H2 → Alkane

Heat evolved upon catalytic hydrogenation (△Ho)A MEASURE OF ALKENE STABILITY

ALKENEC4H8

ALKANEC4H10H2/Pd-C

EXOTHERMIC

Best to compare compounds that reactto form same alkane

Trans > Cis > Geminal

ENERGY

(-) 27.4kcal/mol

(-) 28.3kcal/mol

(-) 30.3kcal/mol

SUMMARY OF ALKENE CHEMISTRY(illustrated with 1-methyl cyclopent-1-ene to emphasize transformation stereochemistry)

POLYOL NATURAL PRODUCTS

ERYTHRONOLIDE A (ERYTHROMYCIN A)

Antibiotic

CELLULOSE

Antifungal

AMPHOTERICIN B

NATURAL PRODUCTS WITH ALKENE FUNCTIONALITY

-BisaboleneA sesquiterpene found in the essentialoils of a number of plants

CembreneA diterpene from pine needles

LimoneneA monoterpenecommon in citrus fruits

-Carotene (A vitamin)A tetraterpene bright orange incolor and the precursor to thevisual pigment retinal

CaryophylleneA constituent of cloveoil

CarvoneSpearmint oil

Vitamin A (vision)

MARKOVNIKOV and ANTI-MARKOVNIKOV ADDITION TO ALKENES

In the dark, in the absence ofperoxides polar solvents topromote formation of polarintermediate.Most substituted carbonium ionintermediate gives mostsubstituted bromide product

In the presence of peroxidesand heat or light to promotehomolytic cleavage of O-Obond.Most substituted radicalintermediate gives leastsubstituted bromide product

Anti-Markovnikov

Markovnikov

ALKENE POLYMERIZATION - SPECIAL TOPIC

MONOMER STRUCTURE

ethene

propene

Chloroethene (vinyl chloride)

POLYMER (trade name)

Polyethylene(polythene)

Random co-polymerSARAN WRAP

tetrafluoroethene

acrylonitrile

1,1-dichloroetheneand 1-chloroethene

methylmethacrylate

Phenylethene(styrene)

Orlon(acrilan)

TEFLON

POLYSTYRNEN

LUCITE(Plexiglass)

polypropylene

PVC(poly)vinyl chloride

FREE RADICAL POLYMERIZATIONINITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS

TERMINATION

POLYMERIZATION

INITIATION

FREE RADICAL POLYMERIZATIONINITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS

TERMINATION

POLYMERIZATION

INITIATION

FREE RADICAL POLYMERIZATIONINITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS

INITIATION

POLYMERIZATION

TERMINATION

CATIONIC POLYMERIZATIONINITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS

INITIATION

POLYMERIZATION

TERMINATION

Good monomer for cationicpolymerization..Why?

What abouttetrafluoroethene?

CHOLESTEROL BIOSYNTHESIS

Squalene

Oxidosqualenecyclase

Squaleneepoxidase

CHOLESTEROL

Oxidosqualenecyclase