JC1 H2 Chemistry - Alkenes Flashcards

Vocabulary flashcards for Alkenes based on lecture notes.

Alkene

Unsaturated hydrocarbons containing one or more C=C double bonds.

General formula of alkenes

CnH2n

Hybridization of C in C=C

sp2 hybridized

Geometry around double bonded C

Trigonal planar

Sigma (σ) bond formation in ethene

Overlap of sp2 hybrid orbitals head-on.

Pi (π) bond formation in ethene

Side-on overlap of unhybridized 2p orbitals.

IUPAC nomenclature suffix for alkenes

-ene

Diene

Molecule with two C=C double bonds.

Constitutional Isomers

Isomers with the same molecular formula but different structural formulae.

Cis-trans Isomers

Isomers with the same molecular and structural formula but different spatial arrangements due to restricted rotation about a bond.

Condition for cis-trans isomerism

Presence of C=C double bond and two different groups attached to each C atom of the C=C.

Boiling point trend with chain length in alkenes

Boiling point increases as the carbon atoms increase.

Boiling point: branched vs straight chain alkenes

Branched chain alkenes have lower boiling points than straight chain alkenes.

Boiling point: cis- vs trans-isomers

Cis-isomers generally have higher boiling points than trans-isomers.

Solubility of alkenes in water

Insoluble due to non-polar nature.

Cracking of alkanes

A method to prepare alkenes

Elimination Reaction

Involves the removal of atoms or groups of atoms from two adjacent carbon atoms to form a carbon-carbon double bond.

Dehydration of alcohols

Elimination of water (H2O) from alcohols using conc. H2SO4, conc. H3PO4 or Al2O3.

Saytzeff’s Rule

The most substituted alkene will be the most stable product and is thus the major product in elimination reactions.

Dehydrohalogenation

Elimination of hydrogen halide (HX) from halogenoalkanes using KOH in ethanol.

Electrophilic Addition

An addition reaction in which an electron-rich molecule donates a pair of electrons to an electrophile.

Markovnikov's Rule

In the addition of HX to an unsymmetrical alkene, the H atom adds to the carbon of the double bond with the greater number of hydrogen atoms.

Hydration

Electrophilic addition of water/steam to alkenes using concentrated H3PO4 or concentrated H2SO4.

Mild Oxidation of Alkenes

Reaction with cold KMnO4 to form a diol.

Strong Oxidation of Alkenes

Reaction with hot KMnO4 to cleave the C=C bond, forming carboxylic acids, ketones, or CO2 and H2O.