Lecture Notes – Alkanes & Related Concepts

These question-and-answer flashcards review definitions, naming rules, structural concepts, physical properties, reactions, and environmental aspects of alkanes and related compounds from the lecture notes.

What is the general definition of an organic compound?

A molecular compound containing carbon, excluding CO, CO₂, and HCN.

Why can carbon form a wide variety of molecules?

It has 4 valence electrons, enabling it to form four covalent bonds and create chains or rings.

Define hydrocarbon.

A compound composed only of carbon and hydrogen atoms.

What is a saturated hydrocarbon (alkane)?

A hydrocarbon in which all carbon–carbon bonds are single bonds.

State the general formula for alkanes.

CₙH₂ₙ₊₂

What is the simplest alkane and its formula?

Methane, CH₄.

Describe the molecular geometry of methane.

Tetrahedral around the carbon atom.

Give the names and molecular formulas of the first four alkanes.

Methane CH₄, Ethane C₂H₆, Propane C₃H₈, Butane C₄H₁₀.

What prefix indicates five carbon atoms in an alkane?

Pent- (as in pentane).

What is a straight-chain alkane?

An alkane whose carbon atoms are connected in one continuous chain.

Why do straight-chain alkanes have a zig-zag shape in space?

Because the tetrahedral C–C–C bond angle is 109.5°, not 180°.

Define cyclic alkane (cycloalkane).

A hydrocarbon in which the carbon atoms form a closed ring.

Give the simplest cycloalkane and its formula.

Cyclopropane, C₃H₆.

What is the general formula for cyclic alkanes?

CₙH₂ₙ

In a line diagram, what is located at every end or intersection of a line?

A carbon atom (surrounded by the appropriate number of hydrogens).

Define alkyl group.

One or more carbon atoms that form a branch off the main chain of a hydrocarbon.

What is a substituent group?

Any atom or group that replaces a hydrogen atom in an organic compound.

Define structural isomer.

Compounds with the same molecular formula but different bonding arrangements.

Give an example pair of structural isomers with formula C₄H₁₀.

Butane (straight chain) and methylpropane (branched).

List the five basic steps for naming branched alkanes (IUPAC).

1) Identify the longest carbon chain (parent). 2) Identify all substituent groups. 3) Number the chain to give substituents the lowest possible numbers, using alphabetical order to break ties. 4) Use prefixes di-, tri-, etc. for multiple identical substituents and list their positions. 5) Write the name: numbers separated by commas, words by hyphens, substituents in alphabetical order (ignoring prefixes).

How are cyclic hydrocarbons named?

Name the ring size as a cyclo- parent; number the ring to give substituents the lowest set of numbers.

What physical property trend is observed as alkane chain length increases?

Boiling and melting points increase because of stronger van der Waals forces.

Why are alkanes considered non-polar?

Carbon and hydrogen have similar electronegativities, so C–H bonds are almost non-polar and molecular geometry distributes charge evenly.

Explain complete combustion of a hydrocarbon.

Reaction with O₂ producing CO₂, H₂O, and thermal energy.

Write the balanced equation for complete combustion of butane.

2 C₄H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O + energy

Why are small alkanes more flammable than long-chain alkanes?

They are gases at room temperature and vaporize easily, allowing rapid mixing with air.

What industrial process separates crude oil into fractions of different alkanes?

Fractional distillation (fractionation).

Give two common uses of alkanes with 1–4 carbon atoms.

Natural gas for heating/cooking and propane or butane for torches or lighters.

Define alkyl halide.

An alkane in which one or more hydrogen atoms have been replaced by halogen atoms.

How are alkyl halides named?

Halogen prefixes (fluoro-, chloro-, bromo-, iodo-) with position numbers are listed alphabetically before the parent alkane name.

Provide the IUPAC name for CH₃CH₂CHBrCH₃.

2-bromobutane.

Why do alkyl halides have higher boiling points than corresponding alkanes?

The C–X bonds are polar, increasing intermolecular (dipole–dipole) forces.

What environmental issue is associated with chlorofluorocarbons (CFCs)?

They reach the stratosphere and degrade ozone, thinning the protective ozone layer.

State the general formula for chlorofluorocarbons mentioned.

CFₓCly (substituted methanes with Cl and F).

What is complete combustion’s environmental concern?

Releases CO₂, a greenhouse gas that contributes to global warming.