Hydrocarbons and Halocarbons – Key Concepts

Fill-in-the-blank flashcards covering foundational terminology, structures, physical and chemical properties, industrial processes, and environmental aspects of hydrocarbons and halocarbons.

The belief that organic compounds could only be created by living organisms was called the __ theory.

vital force (vis vitalis)

In 1828, __ synthesized urea from ammonium cyanate, disproving vitalism.

Friedrich Wöhler

Today, organic chemistry is defined as the chemistry of __ compounds.

carbon

Lavoisier identified C, H, O, and N as the main constituents of organic compounds, naming them __ elements.

organogenic

The six major biogenic elements are…

C,H,O,N,P,S

Because of its small atomic size and EN 2.5, carbon forms very strong __ bonds.

covalent

Due to sp³ hybridisation, a carbon atom can form _ strong covalent bonds in a tetrahedral geometry.

four

Atoms other than C and H within an organic chain are called __.

heteroatoms

An atom or group of atoms that determines a compound’s properties is called a __ group.

functional

Compounds with the same molecular formula but different structure exhibit __.

isomerism

Isomers differing in bonding order are called __ isomers.

constitutional

Isomers with the same constitution but different spatial arrangement are __.

stereoisomers

The general molecular formula for open-chain saturated hydrocarbons (alkanes) is __.

CₙH₂ₙ₊₂

Members of a homologous series differ from each other by one __ group.

CH₂ (methylene)

Removing one hydrogen from an alkane yields an __ group, written as R-.

alkyl

In naming branched alkanes, the longest chain with the most branches is called the __ chain.

parent (main)

Carbon atoms attached to only one other carbon are called __ carbons.

primary (1°)

Closed-chain saturated hydrocarbons are known as __.

cycloalkanes

The general molecular formula of cycloalkanes is __.

CₙH₂ₙ

Methane molecules are non-polar and are held together in the liquid/solid state by weak __ forces.

dispersion

Because it is colourless, odourless, and flammable, methane used as piped gas must have an __ added for safety.

odorant

Methane is a major __ gas, strongly contributing to the greenhouse effect.

greenhouse

The balanced equation for the complete combustion of methane is CH₄ + __ O₂ → CO₂ + 2 H₂O.

2

Thermal decomposition of methane at ~1000 °C produces ethyne and hydrogen via free __.

radicals

Substitution of methane with chlorine is initiated by __ light or high temperature.

UV

Among alkanes, C₁–C₄ are gases at room temperature, C₅–C₁₆ are liquids, and from C₁₇ upward they are __.

solids

More highly branched alkanes have __ melting points and lower boiling points than their linear isomers.

higher

The most stable conformer of ethane is the __ conformation.

staggered

The predominant (>99 %) conformer of cyclohexane is the __ form.

chair

Crude oil is separated into fractions by __ distillation.

fractional

The petrol/gasoline fraction contains hydrocarbons with to carbon atoms.

5 to 10

The measure of petrol’s resistance to knocking is its __ number.

octane

An octane number of 100 corresponds to pure __ (2,2,4-trimethylpentane).

isooctane

An octane number of 0 corresponds to __, which knocks readily.

n-heptane

Improving octane number by increasing branched and cyclic hydrocarbons is called petrol __.

reformation

Long-chain alkanes are broken into shorter, more useful molecules in a high-temperature process called __.

cracking

During imperfect combustion of large alkanes, the flame becomes yellow and __ due to soot formation.

sooty (glowing)

The liquid alkanes are good solvents for non-polar substances because of the rule “__ dissolves like.”

like

Particles with an unpaired electron produced during thermal decomposition are called __.

free radicals

Alkanes have the lowest chemical reactivity among organic compounds because of their strong __ bonds.

C–H

A fill-in blank: The substitution reaction C₃H₈ + 2 Cl₂ → C₃H₆Cl₂ + 2 HCl is characteristic of __.

alkanes (and cycloalkanes)

Conformers interconvert by rotation around a __ bond.

sigma (σ)

In the cyclohexane chair, hydrogens parallel to the ring’s symmetry axis are called __ hydrogens.

axial

Natural gas consists mainly of __, with smaller amounts of ethane, propane, and butane.

methane

The fraction used as jet fuel and lamp oil is __ (C₁₁–C₁₂ range).

kerosene

The highly viscous fraction C₁₆–C₂₈ that yields lubricating oil is called __ oil.

diesel (gas) or residue

“Paraffin” comes from the Latin phrase meaning “__ attraction,” reflecting alkanes’ low reactivity.

poor