Alkenes: Structure, Nomenclature, and Chemical Reactions

This set covers the definition, classification, preparation, priority rules for E/Z isomerism, and chemical reactions of alkenes as presented in the lecture notes.

Alkenes

Unsaturated hydrocarbons with a general molecular formula of $C_nH_{2n}$ ($n \ge 2$) containing a $-C=C-$ functional group.

Olefins

A common name for alkenes because they give oily products when they react with halogens.

$sp^2$ hybridization

The hybridization state of the carbon atoms in the functional group of alkenes.

Ethene

The simplest member of the alkene family, with the formula $C_2H_4$.

Combustion of Alkenes

The reaction where alkenes burn in air or oxygen to produce $CO_2$ and $H_2O$ according to the equation: $C_nH_{2n} + \frac{3n}{2}O_2 \rightarrow nCO_2 + nH_2O$.

Dehydration of Alkanols

A preparation method for alkenes involving the removal of water from an alkanol in the presence of $\text{Conc. } H_2SO_4$ at about $170^\circ C$.

Dehydrohalogenation

The removal of a hydrogen atom and one halogen atom from an alkyl halide in the presence of $\text{alcoholic KOH}$ to prepare an alkene.

Dehalogenation

The removal of two halogen atoms from an alkyl dihalide in the presence of Zinc ($Zn$) to form an alkene.

Electrophilic addition

The mechanism by which the major reactions of alkenes occur, where an electrophile attacks the double bond to form a saturated product.

Hydrogenation

The addition of hydrogen to alkenes in the presence of Nickel ($Ni$) or Platinum ($Pt$) catalyst to form an alkane.

Halogenation

The reaction of alkenes with halogens in the presence of $CCl_4$ as an organic solvent to produce a dihaloalkane.

Hydrohalogenation

The addition of a hydrogen halide ($HX$) to an alkene to produce a haloalkane.

Markovnikov’s rule

States that whenever a compound with hydrogen is added to a multiple bond, the hydrogen goes to the carbon atom that has the highest number of hydrogen atoms attached to it.

Anti-Markovnikov’s rule

The addition of $HBr$ in the presence of a peroxide ($H_2O_2$ or $-O-O-$) which causes the reaction to proceed against the standard Markovnikov orientation.

Entgegen (E)

A German word meaning 'across' or 'opposite'; used for isomers where groups of higher priority are on opposite sides of the double bond.

Zusammen (Z)

A German word meaning 'same' or 'together'; used for isomers where groups of higher priority are on the same side of the double bond.

Priority Rule (Atomic Number)

Criteria stating that atoms with higher atomic numbers are of higher priority than atoms with lower atomic numbers (e.g., C > H).

Priority Rule (Isotopes)

Criteria stating that if isotopes are present, the isotope with a higher mass number is of higher priority (e.g., C\text{-}14 > C\text{-}12).