Hydrocarbon Chemistry: Alkanes, Alkenes, Alkynes, and Arenes

Traditional vocabulary flashcards covering key definitions, reactions, laws, and chemical constants for Hydrocarbons as presented in the lecture.

Hydrocarbon

Compounds containing only $C$ and $H$-atoms, with major sources being natural gas, petroleum, and coal.

Alkanes (Paraffins)

Saturated acyclic hydrocarbons with the general formula $C_n H_{2n + 2}$, termed paraffins due to their almost inert nature.

C–C Bond Length (Alkanes)

$$1.54\,\text{Å}$$

C–C Bond Energy (Alkanes)

$$80\,kcal\,mol^{-1}$$

Liquefied Petroleum Gas (LPG)

A fuel mixture composed of propane, butane, and isobutane.

Sodalime

A mixture of $CaO$ and $NaOH$ in a $4 : 1$ ratio used for the decarboxylation of sodium salts of fatty acids to prepare alkanes.

Raney Ni

An alloy of $Ni \text{–} Al$ used as a catalyst in the Sabatier and Senderen Reaction.

Wurtz Reaction

A method to prepare alkanes containing an even number of carbon atoms by treating alkyl halides with sodium metal in the presence of dry ether.

Corey–house synthesis

A method used to prepare unsymmetrical alkanes (possessing odd numbers of carbon atoms) involving dialkyl lithium cuprate (Gilman Reagent).

Kolbe Synthesis

The electrolysis of sodium or potassium salts of monocarboxylic acids to form alkanes at the anode.

Alternation Effect

Also known as the oscillation effect, it refers to alkanes with an even number of carbon atoms having higher melting points than those with an odd number of carbon atoms due to closer packing in the crystal lattice.

Pyrolysis (Cracking)

The thermal breakdown of higher alkanes into lower alkanes, alkenes, and hydrogen in the absence of air.

Alkenes (Olefins)

Unsaturated hydrocarbons with at least one double bond and the general formula $C_n H_{2n}$.

Baeyer’s Reagent

A $1\%$ solution of alkaline $KMnO_4$ used as a test for unsaturation; it decolourises in the presence of alkenes or alkynes.

Zaitsev Rule

A rule used in dehydrohalogenation stating that the more substituted alkene is the major product.

Wittig Reaction

The reaction of a carbonyl compound with a phosphorus ylide (methylene triphenyl phosphorane) to synthesize an alkene.

Markovnikov’s Rule

A regioselectivity rule for addition reactions stating that the acidic hydrogen attaches to the carbon with more hydrogen substituents, while the halide/substituent attaches to the carbon with more alkyl groups.

Peroxide Effect (Kharasch Effect)

The anti-Markovnikov addition of $HBr$ to alkenes in the presence of peroxides.

Hydroboration-oxidation

A two-step process to convert alkenes into neutral alcohols following anti-Markovnikov regioselectivity.

Alkynes

Unsaturated hydrocarbons with at least one triple bond and the general formula $C_n H_{2n - 2}$; they are linear and $sp$ hybridized.

Lindlar’s Catalyst

$CaCO_3$ poisoned with sulphur or $Pd \text{–} BaSO_4$ used to facilitate the partial reduction of alkynes to cis-alkenes.

Huckel’s Rule

A rule for aromaticity stating that a planar, cyclic, conjugated system must possess $(4n + 2) \pi$ electrons.

BTX

The high-demand hydrocarbons found in the light oil fraction of coal tar, consisting of benzene ($72\%$), toluene ($13\%$), and xylene ($4\%$).

Friedel–Crafts Reaction

The electrophilic substitution of a hydrogen atom on a benzene ring with an alkyl or acyl group in the presence of a Lewis acid catalyst like anhydrous $AlCl_3$.

Octane Number

A measure of automobile fuel quality defined by the percentage of iso-octane ($2, 2, 4 \text{-} \text{trimethyl pentane}$) in a mixture with n-heptane.

Knocking

A metallic sound in an internal combustion engine caused by the pre-ignition of fuel; straight-chain alkanes produce the highest knocking.

TEL (Tetraethyl lead)

A chemical compound with the formula $(C_2 H_5)_4 Pb$ used as an anti-knocking agent for gasoline.

Cetane Number

The percentage of cetane (hexadecane) in a diesel sample, used to measure diesel fuel quality.

Flash Point

The minimum temperature at which an oil gives off enough vapours to form a momentary flash of light upon exposure to a flame.

Mustard Gas

A poisonous gas formed by the reaction of ethylene ($C_2 H_4$) with sulphur monochloride ($S_2 Cl_2$).